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Corn Gluten Meal and Corn Gluten Hydrolysate for Weed Control

by Melissa Caroline McDade

A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Major: Horticulture
Major Professor: Nick E. Christians
Iowa State University
Ames, Iowa
1999

Concern over the long-term ecological effects of synthetic agricultural chemicals has led to increased efforts in the search for natural products (Cardellina, 1988). Weeds were considered the most important pest group for farmers interested in lowering external inputs and avoiding synthetic chemical use. Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass that reduces germination of many broadleaf and grass weeds. The objective of this study was to investigate weed cover and vegetable seedling survival in field plots when CGM is incorporated before planting. Three studies were conducted with three replications for each study. Five rates of powdered CGM (0, 100, 200, 300, and 400 g m-2) were weighed and incorporated into the top 5-8 cm of soil in recently disked 1.5 m by 2.7 m plots. Seeds of eight vegetables were planted in rows 1.4 m long and 0.3 m apart. Seedling survival and percent weed cover were recorded for each plot. The CGM at rates of 100, 200, 300 and 400 g m-2 reduced percent weed cover by 53, 76, 85, and 83%, respectively, compared to the control. Seedling survival at 100 g CGM per m2 was reduced by 67% for ‘Comanche’ onion (Allium cepa L.), 35% for ‘Ruby Queen’ beet (Beta vulgaris L.), 41% for ‘Red Baron’ radish (Raphanus sativus L.), 71% for ‘Provider’ bean (Phaseolus vulgaris L.), 73% for ‘Scarlet Nantes’ carrot (Daucus carota L. subsp. sativus), 59% for ‘Maestro’ pea (Pisum sativum L.), and 68% for ‘Black Seeded Simpson’ lettuce (Lactuca sativa L.), compared to the control. Seedling survival for ‘Daybreak’ sweet corn (Zea mays L.) was not significantly reduced by rates of 100 or 200 g CGM per m2, but was reduced by 26% at a rate of 300 g CGM per m2 compared to the control. Because of the reduction in seedling survival at even the lowest rate of CGM (100 g m-2), direct seeding into soil into which CGM has been incorporated is not advisable. Transplants may be an alternative to take advantage of the herbicidal effects of CGM and the nitrogen it provides.

Corn gluten hydrolysate is a water-soluble product derived from corn gluten meal through enzyme hydrolysis. The CGH has been identified as a natural preemergence herbicide in greenhouse studies. The objectives of this study were to test humic acid and soybean oil for their capacity to improve the herbicidal and fertilization activity of CGH and to investigate CGH for crabgrass (Digitaria spp.) control in turf in the field. We used CGH at rates of 0, 100, 200, and 400 g m-2, humic acid at 0, 0.93, 1.9, 3.7 and 7.5 ml m-2, and soybean oil at 0, 58, 120, 180, and 230 m l m-2 in greenhouse studies with seeds of perennial ryegrass (Lolium perenne L.). In the field, four rates of CGH (0, 50, 100, and 200 g m-2), humic acid (0, 0.93, 1.9 and 4.1 ml m-2) and soybean oil (0, 59, 120, and 230 m l m-2), were applied to a mature stand of Kentucky bluegrass (Poa pratensis L.). Neither humic acid nor soybean oil affected the performance of CGH in either study. In the greenhouse study, ryegrass seedling survival was decreased by 0, 24, and 65% compared to the control at CGH rates of 100, 200 and 400 g m-2, respectively. In the field study, plots treated with CGH at 200 g m-2 had 69 and 93% fewer crabgrass plants in the 1998 and 1999 studies, respectively, compared to the control. Plots treated with 200 g CGH per m2 had the highest visual quality compared to the control in both field studies. Corn gluten hydrolysate has the potential to be used as a natural weed control and fertilizer product in turfgrass, but its activity is not enhanced by humic acid or soybean oil.

CHAPTER 1. GENERAL INTRODUCTION

Concern over the long-term ecological effects of synthetic agricultural chemicals has led to increased efforts in the search for natural products (Cardellina, 1988). Allelopathic chemicals found in natural products may be used directly as herbicides and to develop new classes of synthetic herbicides based on natural chemicals (Narwal, 1996). Corn gluten meal (CGM) has been identified as an effective natural preemergence herbicide for use in turfgrass and other crops (Bingaman and Christians, 1995; Christians, 1993; Nonnecke and Christians, 1993).

The CGM reduces germination of many broadleaf and grass weeds (Bingaman and Christians, 1995). The CGM allows seedling shoots to emerge, but inhibits root development. After a period of water stress, the seedlings wilt and die because they do not have an adequate root system. A previous study determined that CGM reduces weed cover in bare-soil plots when CGM is incorporated into the soil prior to planting dormant strawberry (Fragaria ´ ananassa Duch.) crowns (Nonnecke and Christians, 1993). Broccoli (Brassica oleracea L. var. italica L.) and cauliflower (Brassica oleracea L. var. botrytis L.) were transplanted into soil into which CGM had been incorporated, and no negative effects on the transplants’ dry root or shoot weights were noted (see Appendix 1). The CGM is currently available in a pelletized form, but is not as easily applied as soluble herbicide materials.

In an effort to find soluble materials with the same herbicidal effects of the corn gluten meal, other by-products of corn processing from the Grain Processing Corp. in Muscatine, Iowa were investigated. Several of these materials were tested in growth chamber and greenhouse studies. Corn gluten hydrolysate (CGH) was found to be more effective as a preemergence herbicide than the corn gluten meal (Liu et al., 1994).

Corn gluten hydrolysate is a water-soluble product derived from corn gluten meal through enzyme hydrolysis. The CGH is herbicidally active and contains 10 to 14% N by weight (Christians et al., 1994).

Greenhouse tests have shown that CGH has greater herbicidal activity than CGM (Liu et al., 1994). In a preliminary field trial, however, the CGH had varying effects on crabgrass (Digitaria spp.) germination when applied at the same rates as CGM (Bingaman and Christians, 1996). These variable effects could be due to rapid microbial degradation or leaching because of the water solubility of CGH.

Humic acid and soybean oil are carriers that could potentially enhance the activity of CGH in the field. Combinations of herbicides and humic substances caused a reduction in root length in pea (Pisum sativum L.) (Senesi and Loffredo, 1994). Herbicides may be adsorbed by organic matter in the soil (Stevenson, 1994) and humic acid may act as a chelating agent to form complexes with cations in the soil (Olmos et al., 1998). Humic acid may form chelates with the CGH to keep it active in the soil and prevent it from leaching. Crop oil concentrates are spray adjuvants which increase the activity of a number of postemergence herbicides (Penner et al., 1983). Soybean oil mixed with herbicides had greater control over certain weeds compared to the control (Kelley et al., 1983; Chaney and Kapusta, 1983), and if used with CGH, could enhance the activity of the CGH.

Thesis Organization

This thesis has five chapters. The first chapter provides a general introduction to the thesis. The second chapter is a review of the literature related to this thesis. Chapter 3 is a manuscript to be submitted to American Journal of Alternative Agriculture. Chapter 4 is a manuscript to be submitted to International Turfgrass Society Research Journal. Chapter 5 gives the general conclusions of the thesis. Each chapter is followed by the references used for that chapter.

References

Bingaman, B.R. and N.E. Christians. 1995. Greenhouse screening of corn gluten meal as a natural control product for broadleaf and grass weeds. HortScience 30:1256-1259.

Bingaman, B.R. and N.E. Christians. 1996. 1995 corn gluten hydrolysate weed control study. 1996 Iowa Turfgrass Res. Rpt. Iowa State Univ. Ext., Ames, Iowa.

Cardellina, J.H., II. 1988. Natural products in the search for new agrochemicals, p. 305-315. In: H.G. Cutler (ed.). Biologically active natural products: potential use in agriculture. Amer. Chem. Soc., Washington, D.C.

Chaney, D. and G. Kapusta. 1983. Evaluation of soybean oil concentrate vs. petroleum oil concentrate with postemergence soybean herbicides. North Central Weed Control Conf. Proc. 38:25.

Christians, N.E. 1993. The use of corn gluten meal as a natural preemergence weed control in turf. Intl. Turfgrass Soc. Res. J. 7: 284-290.

Christians, N.E., J.T. Garbutt, and D. Liu. 1994. Preemergence weed control using plant portein [sic] hydrolysate. U.S. Patent No. 5,290,749.

Kelley, G., W.W. Witt, and C. Slack. 1983. Soybean oil as an additive for broadleaf postemergence herbicides. North Central Weed Control Conf. Proc. 38:17.

Liu, D.L.-Y., N.E. Christians, and J.T. Garbutt. 1994. Herbicidal activity of hydrolyzed corn gluten meal on three grass species under controlled environments. J. Plant Growth Regul. 13:221-226.

Narwal, S.S. 1996. Potentials and prospects of allelopathy mediated weed control for sustainable agriculture, p. 23-26. In: S.S. Narwal and P. Tauro (eds.). Allelopathy in pests management for sustainable agriculture. Sci. Publishers, Jodhpur, India.

Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of corn gluten meal as a natural, weed control product in strawberry. Acta Hort. 348:315-320.

Olmos, S., E. Esteban, and J.J. Lucena. 1998. Micronutrient extraction in calcareous soils treated with humic concentrates. J. Plant Nutrition 21:687-697.

Penner, D., F.C. Roggenbuck, and K. Van Fletern. 1983. Rapid evaluation of soybean oil in crop oil concentrates. North Central Weed Control Conf. Proc. 38:124.

Senesi, N. and E. Loffredo. 1994. Influence of soil humic substances and herbicides on the growth of pea (Pisum sativum L.). J. Plant Nutrition 17:493-500.

Stevenson, F.J. 1994. Humus chemistry: genesis, composition, reactions. 2nd ed. Wiley, New York.

CHAPTER 2. LITERATURE REVIEW

Environmental Concerns about Pesticide Use

Synthetic pesticides are used currently for agricultural production and for the maintenance of landscaped areas. Pesticide use on areas such as golf courses and parks is a concern to many people who use these areas. Agricultural workers may be exposed to pesticides during or after application. Safety issues are not confined to direct contact with pesticides, but also involve the environmental issues of pesticide runoff, groundwater contamination and the effects of pesticides on non-target plants and animals.

Turfgrass plays an important role in landscapes, helping to prevent soil erosion and providing a playing surface for sports (Beard and Green, 1994). Many of these areas are managed intensively to control pests and provide high-quality turf (Balogh and Anderson, 1992). While many of the chemicals in use are considered safe when used as directed, common pesticides can have unintended consequences, such as harming non-target organisms (Potter et al., 1990), contributing to pest resistance to pesticides (Curtis et al., 1991), and contaminating ground water (Balogh and Anderson, 1992). The public has become concerned with nutrient and pesticide contamination of ground and surface water (Balogh et al., 1992) and the potential risks of contamination (Balogh and Anderson, 1992). Public concern has increased research on pesticide movement through soil profiles under turfgrass (Smith et al., 1993) and fueled the search for natural products for pest control. The discovery of natural products would be especially welcome for residential consumers, many of whom want alternatives to chemical pesticides for their lawns and gardens.

Natural Products

Concern over the long-term ecological effects of synthetic agricultural chemicals has led to increased efforts in the search for natural products (Cardellina, 1988). Allelopathic chemicals found in natural products may be used directly as pesticides and to develop new classes of synthetic pesticides based on natural chemicals (Narwal, 1996). This has been successful in a class of insecticide. Pyrethroids are synthetic insecticides based on pyrethrins, which are naturally occurring chemicals found in the pyrethrum extract of several species of Chrysanthemum (Casida and Quistad, 1995).

Early research found that decomposing plant residues contain a toxic substance which inhibits germination of some seeds (Nielsen et al., 1960; Patrick, 1971). Extracts of corn (Zea mays L.) residue taken during decomposition had inhibitory effects on seedlings (Guenzi et al., 1967) and suppressed root elongation in lettuce seeds (Chou and Patrick, 1976). Corn pollen reduced radicle growth of seeds in another study (Jiménez et al., 1983). These studies found little inhibitory effect by the seed or its extracts. More recent studies have found germination inhibition by products of the corn seed itself: corn gluten meal (Christians, 1991) and corn gluten hydrolysate (Christians et al., 1994b). Gough and Carlstrom (1999) have reported that wheat gluten meal also inhibits germination of some weed species in the greenhouse.

Corn Gluten Meal

Corn gluten meal (CGM) has been identified and patented as a natural preemergence herbicide for use in turfgrass and other crops (Bingaman and Christians, 1995; Christians, 1991; Christians, 1993; Nonnecke and Christians, 1993). The CGM is a by-product of the corn wet-milling process and is used for animal feed. The Environmental Protection Agency (EPA) ruled that CGM is exempt from the requirement of a tolerance for residues and does not require Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) regulation (EPA, 1997). The CGM is a preemergence herbicide that acts on germinating seeds. Seedling shoots emerge normally, but the development of the emerging root is inhibited. After a period of water stress, the seedlings wilt and die because they do not have an adequate root system. The CGM also contains 10% nitrogen by weight, and has a fertilizing effect when applied to turfgrass (Christians, 1993).

Corn gluten meal in turfgrass

Most studies with CGM have focused on turfgrass. The combination of preemergence weed control and nitrogen source makes corn gluten meal a useful product for use in turfgrass. It may be used to control weeds in mature turf without the risk of harming the desirable grass plants, and fertilizes the mature turf, as well. Studies with pendimethalin, a common preemergence herbicide, indicate that using CGM in a combination with the herbicide reduced the amount of pendimethalin needed for weed control in turfgrass (Gardner et al., 1997).

Corn gluten meal in other production systems

Organic farming is still a small subset of U.S. agriculture, but it is a segment which is growing rapidly (Fernandez-Cornejo et al., 1998). Organic production has become an important way to keep agriculture viable near populated areas, since organic farms generally are smaller scale, do not use chemical sprays, and may market directly to consumers (Lockeretz, 1995). Organic producers are often involved in raising food crops, since consumers are willing to pay a premium on organically produced foods (Fritz, 1989). Consumers cite health, taste, higher nutritive value, and the environment as reasons why they prefer to purchase organically produced foods (Sylvander, 1993).

Consumers are assured through a certification program that the organic products they purchase have not been treated with synthetic chemicals, and are willing to pay a premium for that assurance. For these reasons, certification of organic products is important. Certification is based on the production practices used by organic producers (Grubinger, 1992). There are several certifying agencies in the U.S., including California Certified Organic Farmers (CCOF) and the Organic Crop Improvement Association (OCIA). National standards set by the National Organic Program (NOP) of the U.S. Department of Agriculture (USDA) are currently in review. These agencies have similar recommendations for materials to be used in organic production (Fernandez-Cornejo et al., 1998). Synthetic chemicals are not allowed for pest control and nutrient addition, but positive practices, such as organic matter and crop rotations, must be used in place of negative (chemical) inputs (Fritz, 1989).

A study of organic and conventional growers in Denmark showed that both groups perceive the same pests and diseases as the most serious (Langer, 1995). Weeds were considered the most important pest group in a survey of organic vegetable growers in the U.K. (Peacock and Norton, 1990). The most often cited problems were lack of adequate pest controls and labor/capital constraints, particularly with respect to weeds (Peacock and Norton, 1990). Some weed control practices in use include cover crops, mulches (Wallace and Bellinder, 1992), crop rotations, biological control, smother crops (Markey, 1990), intercropping, and intensive planting (Jesiolowski, 1993). These practices have varying degrees of effectiveness: biological control can be limited by the availability of natural predators; mechanical control can be expensive, especially if hand-weeding is needed; and most methods include the need for crop monitoring, which takes time and knowledge (Putnam, 1990). Animal manures and legumes may be used for nutrient sources in crop production, but there are problems with expense and availability in some areas of the U.S. (Kelly, 1990). With the increasing markets for organic products, improved organic crop protection methods, including organic approaches to nutrient management (Grubinger, 1992), need to be researched and developed (Peacock and Norton, 1990). The CGM is a product that may be used for both weed control and nutrient addition in organic systems.

The CGM reduces germination of many broadleaf and grass weeds (Bingaman and Christians, 1995). The CGM also reduces percent weed cover in bare-soil plots when it is incorporated into the soil prior to planting dormant strawberry (Fragaria ´ ananassa Duch.) crowns and greenhouse studies showed no detrimental effects to growth and development of the strawberry plant (Nonnecke and Christians, 1993). Broccoli (Brassica oleracea L. var. italica L.) and cauliflower (Brassica oleracea L. var. botrytis L.) were transplanted into soil into which CGM had been incorporated, and the transplants’ dry root and shoot weights were not negatively affected (see Appendix 1). The first study investigates vegetable seed germination and weed cover in plots where CGM is incorporated before planting.

Corn Gluten Hydrolysate

The CGM is used in pelletized and powdered forms, both of which have herbicidal activity, but are not water soluble. In an effort to find soluble materials with the same herbicidal effects of the corn gluten meal, other by-products of corn processing from the Grain Processing Corp. in Muscatine, Iowa were investigated. Several of these materials were tested in growth chamber and greenhouse studies and corn gluten hydrolysate (CGH) was found to be a soluble product with more herbicidal activity than CGM (Liu et al., 1994).

The CGH is formed by treating an aqueous slurry of corn plant protein with an amylase and then a protease. The resulting filtrate contains the CGH and can be evaporated and then spray dried. The dry product of CGH is water soluble (Christians et al., 1994b).

The water-soluble CGH is herbicidally active and contains 10 to 14% N by weight (Christians et al., 1994b; Liu and Christians, 1997; Liu et al., 1994). Five dipeptides and one pentapeptide that had inhibitory effects on the root growth of germinating seeds were isolated from CGH (Christians et al., 1994a; Liu and Christians, 1994; Liu and Christians, 1996). One dipeptide, alaninyl-alanine, was tested and found to cause epidermal necrosis at high concentrations and disruption of cellular processes at lower concentrations in root tissue (Unruh et al., 1997).

Greenhouse tests have shown that CGH has greater herbicidal activity than CGM (Liu et al., 1994). In a preliminary field trial, however, CGH had varying effects on crabgrass (Digitaria spp.) control when applied at the same rates as CGM (Bingaman and Christians, 1996). These variable effects could be due to rapid microbial degradation or leaching because of CGH’s water solubility. Humic acid and soybean oil are carriers that could potentially enhance the activity of CGH in the field. Combinations of herbicides and humic substances caused a reduction in root length in pea (Pisum sativum L.) (Senesi and Loffredo, 1994). Herbicides may be adsorbed by organic matter in the soil (Khan, 1974; Stevenson, 1994) and humic acid may act as a chelating agent to form complexes with cations in the soil (Olmos et al., 1998). Humic acid may form chelates with CGH to keep it active in the soil and prevent it from leaching. Crop oil concentrates are spray adjuvants which increase the activity of a number of postemergence herbicides (Penner et al., 1983). Soybean oil mixed with herbicides had greater control over certain weeds compared to the control (Kelley et al., 1983; Chaney and Kapusta, 1983), and if used with CGH, could enhance the activity of the CGH. The second study investigates the effects of using humic acid and soybean oil with CGH for enhanced weed control and fertilizer effect.

References

Balogh, J.C. and J.L. Anderson. 1992. Environmental impacts of turfgrass pesticides, p. 221-353. In: J.C. Balogh and W.J. Walker (eds.). Golf course management and construction: environmental issues. Lewis, Chelsea, Mich.

Balogh, J.C., V.A. Gibeault, W.J. Walker, M.P. Kenna, and J.T. Snow. 1992. Background and overview of environmental issues, p. 1-37. In: J.C. Balogh and W.J. Walker (eds.). Golf course management and construction: environmental issues. Lewis, Chelsea, Mich.

Beard, J.B. and R.L. Green. 1994. The role of turfgrasses in environmental protection and their benefits to humans. J. Environ. Qual. 23:452-460.

Bingaman, B.R. and N.E. Christians. 1995. Greenhouse screening of corn gluten meal as a natural control product for broadleaf and grass weeds. HortScience 30:1256-1259.

Bingaman, B.R. and N.E. Christians. 1996. 1995 corn gluten hydrolysate weed control study. 1996 Iowa Turfgrass Res. Rpt. Iowa State Univ. Ext., Ames, Iowa.

Cardellina, J.H., II. 1988. Natural products in the search for new agrochemicals, p. 305-315. In: H.G. Cutler (ed.). Biologically active natural products: potential use in agriculture. Amer. Chem. Soc., Washington, D.C.

Casida, J.E. and G.B. Quistad. 1995. Pyrethrum flowers: production, chemistry, toxicology and uses. Oxford University Press, N.Y.

Chaney, D. and G. Kapusta. 1983. Evaluation of soybean oil concentrate vs. petroleum oil concentrate with postemergence soybean herbicides. North Central Weed Control Conf. Proc. 38:25.

Chou, C.-H. and Z.A. Patrick. 1976. Identification and phytotoxic activity of compounds produced during decomposition of corn and rye residues in soil. J. Chem. Ecol. 2:369-387.

Christians, N.E. 1991. Preemergence weed control using corn gluten meal. U.S. Patent No. 5,030,268

Christians, N.E. 1993. The use of corn gluten meal as a natural preemergence weed control in turf. Intl. Turfgrass Soc. Res. J. 7: 284-290.

Christians, N.E., J.T. Garbutt, and D. Liu. 1994a. Preemergence weed control using dipeptides from corn gluten hydrolysate. U.S. Patent No. 5,290,757.

Christians, N.E., J.T. Garbutt, and D. Liu. 1994b. Preemergence weed control using plant portein [sic] hydrolysate. U.S. Patent No. 5,290,749.

Curtis, J., L. Mott, and T. Kuhnle. 1991. Harvest of hope: the potential for alternative agriculture to reduce pesticide use. Natural Resources Defense Council, New York.

Environmental Protection Agency. 1997. Corn Gluten; exemption from the requirement of a tolerance. EPA, Washington, D.C.

Fernandez-Cornejo, J., C. Greene, R. Penn, and D. Newton. 1998. Organic vegetable production in the U.S.: certified growers and their practices. Amer. J. Alternative Ag. 13:69-78.

Fritz, S. 1989. Organic foods and the vegetable industry. Acta Hort. 247: 397-402.

Gardner, D.S., N.E. Christians, and B.R. Bingaman. 1997. Pendimethalin and corn gluten meal combinations to control turf weeds. Crop Sci. 37:1875-1877.

Gough, R.E. and R. Carlstrom. 1999. Wheat gluten meal inhibits germination and growth of broadleaf and grassy weeds. HortScience 34:269-270.

Grubinger, V.P. 1992. Organic vegetable production and how it relates to LISA. HortScience 27: 759-760.

Guenzi, W.D., T.M. McCalla, and F.A. Norstadt. 1967. Presence and persistence of phytotoxic substances in wheat, oat, corn, and sorghum residues. Agron J. 59:163-165.

Jesiolowski, J. 1993. Super secrets of successful weed warriors. Organic gardening 40(6):26-30.

Jiménez, J.J., K. Schultz, A.L. Anaya, J. Hernández, O. Espejo. 1983. Allelopathic potential of corn pollen. J. Chem. Ecol. 9:1011-1025.

Kelley, G., W.W. Witt, and C. Slack. 1983. Soybean oil as an additive for broadleaf postemergence herbicides. North Central Weed Control Conf. Proc. 38:17.

Kelly, W.C. 1990. Minimal use of synthetic fertilizers in vegetable production. HortScience 25: 168-169.

Khan, S.U. 1974. Adsorption of bipyridylium herbicides by humic acid. J. Environ. Qual. 3:202-206.

Langer, V. 1995. Pests and diseases in organically grown vegetables in Denmark: a survey of problems and use of control methods. Biol. Ag. and Hort. 12:151-171.

Liu, D.L.-Y. and N.E. Christians. 1994. Isolation and identification of root-inhibiting compounds from corn gluten hydrolysate. J. Plant Growth Regul. 13:227-230.

Liu, D.L. and N.E. Christians. 1996. Bioactivity of a pentapeptide isolated from corn gluten hydrolysate on Lolium perenne L. J. Plant Growth Regul. 15:13-17.

Liu, D.L. and N.E. Christians. 1997. Inhibitory activity of corn gluten hydrolysate on monocotyledonous and dicotyledonous species. HortScience 32:243-245.

Liu, D.L.-Y., N.E. Christians, and J.T. Garbutt. 1994. Herbicidal activity of hydrolyzed corn gluten meal on three grass species under controlled environments. J. Plant Growth Regul. 13:221-226.

Lockeretz, W. 1995. Organic farming in Massachusetts: an alternative approach to agriculture in an urbanized state. J. Soil and Water Conservation 50:663-667.

Markey, A.E. 1990. Low input weed management. Amer. Veg. Grower 38(1):30-32.

Narwal, S.S. 1996. Potentials and prospects of allelopathy mediated weed control for sustainable agriculture, p. 23-26. In: S.S. Narwal and P. Tauro (eds.). Allelopathy in pests management for sustainable agriculture. Sci. Publishers, Jodhpur, India.

Nielsen, K.F., T.F. Cuddy, and W.B. Woods. 1960. The influence of the extract of some crops and soil residues on germination and growth. Can. J. Plant Sci. 40:188-197.

Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of corn gluten meal as a natural, weed control product in strawberry. Acta Hort. 348:315-320.

Olmos, S., E. Esteban, and J.J. Lucena. 1998. Micronutrient extraction in calcareous soils treated with humic concentrates. J. Plant Nutrition 21:687-697.

Patrick, Z.A. 1971. Phytotoxic substances associated with the decomposition in soil of plant residues. Soil Sci. 111:13-18.

Peacock, L. and G.A. Norton. 1990. A critical analysis of organic vegetable crop protection in the U.K. Agr. Ecosyst. Environ. 31: 187-197.

Penner, D., F.C. Roggenbuck, and K. Van Fletern. 1983. Rapid evaluation of soybean oil in crop oil concentrates. North Central Weed Control Conf. Proc. 38:124.

Potter, D.A., M.C. Buxton, C.T. Redmond, C.G. Patterson, and A.J. Powell. 1990. Toxicity of pesticides to earthworms (Oligochaeta: Lumbricidae) and effect on thatch degradation in Kentucky bluegrass turf. J. Econ. Entomol. 83:2362-2369.

Putnam, A.R. 1990. Vegetable weed control with minimal herbicide inputs. HortScience 25:155-158.

Senesi, N. and E. Loffredo. 1994. Influence of soil humic substances and herbicides on the growth of pea (Pisum sativum L.). J. Plant Nutrition 17:493-500.

Smith, A.E., O. Weldon, W. Slaughter, H. Peeler, and N. Mantripragada. 1993. A greenhouse system for determining pesticide movement from golf course greens. J. Environ. Qual. 22:864-867.

Stevenson, F.J. 1994. Humus chemistry: genesis, composition, reactions. 2nd ed. Wiley, New York.

Sylvander, B. 1993. Conventions on quality in the fruit and vegetables sector: results on the organic sector. Acta Hort. 340:241-246.

Unruh, J.B., N.E. Christians, and H.T. Horner. 1997. Herbicidal effects of the dipeptide alaninyl-alanine on perennial ryegrass (Lolium perenne L.) seedlings. Crop Sci. 37:208-212.

Wallace, R.W. and R.R. Bellinder. 1992. Alternative tillage and herbicide options for successful weed control in vegetables. HortScience 27:745-749.

CHAPTER 3. CORN GLUTEN MEAL EFFECT ON VEGETABLE SEEDLING SURVIVAL AND WEED COVER

A paper to be submitted to American Journal of Alternative Agriculture

Melissa C. McDade and Nick E. Christians

Abstract

Weeds were considered the most important pest group for farmers interested in lowering external inputs and avoiding synthetic chemical use. Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass that reduces germination of many broadleaf and grass weeds. The objective of this study was to investigate weed cover and vegetable seedling survival in field plots when CGM is incorporated before planting. Three studies were conducted, with three replications for each study. Five rates of powdered CGM (0, 100, 200, 300, and 400 g m-2) were weighed and incorporated into the top 5-8 cm of soil in recently disked 1.5 m by 2.7 m plots. Seeds of eight vegetables were planted in rows 1.4 m long and 0.3 m apart. Seedling survival and percent weed cover were recorded for each plot. The CGM at rates of 100, 200, 300 and 400 g m-2 reduced percent weed cover by 53, 76, 85, and 83%, respectively, compared to the control. Seedling survival at 100 g CGM per m2 was reduced by 67% for ‘Comanche’ onion (Allium cepa L.), 35% for ‘Ruby Queen’ beet (Beta vulgaris L.), 41% for ‘Red Baron’ radish (Raphanus sativus L.), 71% for ‘Provider’ bean (Phaseolus vulgaris L.), 73% for ‘Scarlet Nantes’ carrot (Daucus carota L. subsp. sativus), 59% for ‘Maestro’ pea (Pisum sativum L.), and 68% for ‘Black Seeded Simpson’ lettuce (Lactuca sativa L.), compared to the control. Seedling survival for ‘Daybreak’ sweet corn (Zea mays L.) was not significantly reduced by rates of 100 or 200 g CGM per m2, but was reduced by 26% at a rate of 300 g CGM per m2 compared to the control. Because of the reduction in seedling survival at even the lowest rate of CGM (100 g m-2), direct seeding into soil into which CGM has been incorporated is not advisable. Transplants may be an alternative to take advantage of the herbicidal effects of CGM and the nitrogen it provides.

Introduction

Organic farming is a small subset of U.S. agriculture, but it is a segment which is growing rapidly (Fernandez-Cornejo et al., 1998). Organic producers often raise food crops, since consumers are willing to pay a premium for organically produced foods (Fritz, 1989).

Weeds were considered the most important pest group in a survey of organic vegetable growers in the U.K. (Peacock and Norton, 1990). Growers cited two problems most often: lack of adequate controls and labor/capital constraints, particularly with respect to weeds (Peacock and Norton, 1990). Animal manures and legumes may be used for nutrient sources in vegetable production, but there are problems including expense and availability in some areas of the U.S. (Kelly, 1990). With the increasing market for organic products, improved organic crop protection methods, including organic approaches to nutrient management (Grubinger, 1992), need to be researched and developed (Peacock and Norton, 1990).

Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass (Christians, 1993) that reduces germination of many broadleaf and grass weeds (Bingaman and Christians, 1995). The CGM allows seedling shoots to emerge, but inhibits development of the emerging root. After a period of water stress, the seedlings wilt and die because they do not have an adequate root system. A previous study determined that CGM reduces weed cover in bare-soil plots when CGM is incorporated into the soil prior to planting dormant strawberry (Fragaria ´ ananassa Duch.) crowns (Nonnecke and Christians, 1993). Broccoli (Brassica oleracea L. var. italica L.) and cauliflower (Brassica oleracea L. var. botrytis L.) were transplanted into soil into which CGM had been incorporated, and no negative effects on the transplants’ dry root or shoot weight were noted (see Appendix 1). The objective of this study was to determine the effects on weed cover and vegetable seedling survival when CGM was incorporated into the soil before planting.

Materials and Methods

Field studies were begun on 3 July 1998, 20 Aug. 1998, and 8 June 1999, with three replications for each study. The CGM was applied at rates of 0, 100, 200, 300, and 400 g m-2 and incorporated into the top 5-8 cm of soil in recently disked 1.5 m by 2.7 m plots. Eight vegetables (‘Comanche’ onion (Allium cepa L.), ‘Ruby Queen’ beet (Beta vulgaris L.), ‘Red Baron’ radish (Raphanus sativus L.), ‘Provider’ bean (Phaseolus vulgaris L.), ‘Scarlet Nantes’ carrot (Daucus carota L. subsp. sativus), ‘Maestro’ pea (Pisum sativum L.), ‘Black Seeded Simpson’ lettuce (Lactuca sativa L.), and ‘Daybreak’ sweet corn (Zea mays L.) (Rispens Seeds, Inc., Lansing, Ill.)) were planted in rows 1.4 m long and 0.3 m apart. Onion, beet, and bean seeds were planted 8 cm apart within rows; radish seeds were planted 3 cm apart; carrot and pea were planted 5 cm apart; and lettuce and corn were planted 13 cm apart. After the seedlings emerged, the plots were allowed to dry so that any seedlings with no root would wilt. After the drying period, the site was irrigated as needed when there was no rain. A final count of seedling survival was taken after 3 wks. Percent weed cover was also recorded. The study used a split-plot design and data were analyzed using the general linear models (GLM) procedure in the Statistical Analysis System (SAS) version 6.12 (SAS Institute, 1996).

Results and Discussion

Weather conditions affected the studies: seedlings had the lowest survival rate in the July 1998 study, where hot, dry conditions prevailed. Weed cover was affected in the June 1999 study, which took place during cooler weather. At 21 days after planting (DAP) in the June 1999 study, mean weed cover in the control was 9%, compared to the 1998 studies at 19 and 20 DAP where weed cover was 80 and 50%, respectively.

Weed cover was reduced by 53, 76, 85, and 83% compared to the control by CGM rates of 100, 200, 300 and 400 g m-2, respectively (Table 1). The CGM applied at a rate of 200 g m-2 had the maximum effect on weed control in this study, since the increased control at 300 and 400 g m-2 was not significantly different from the 200 g m-2 rate. The dominant weed in the studies was purslane (Portulaca oleracea L.). Other weeds included common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), ladysthumb (Polygonum persicaria L.), velvetleaf (Abutilon theophrasti Medic.), and foxtail (Setaria spp.). A previous study showed that CGM reduced germination of purslane, common lambsquarters, and redroot pigweed in the greenhouse (Bingaman and Christians, 1995), and percent cover of these weeds was reduced in this field study, likely due to reduced weed seed germination in the field. Field studies with strawberry also showed weed inhibition with applications of CGM (Nonnecke and Christians, 1993).

The CGM applied at rates of 100, 200, 300, and 400 g m-2 reduced overall vegetable seedling survival by 48, 65, 73, and 83%, respectively, compared to the control (Table 2). Like many preemergence herbicides, CGM appears to limit not only weed seed germination, but germination of desirable seeds as well. The CGM significantly reduced the seedling survival of all vegetables compared to the control (Table 2). Seedling survival at 100 g CGM per m2 was reduced by 67% for onion, 35% for beet, 41% for radish, 71% for bean, 73% for carrot, 59% for pea, and 68% for lettuce, compared to the control. Seedling survival for sweet corn was not significantly reduced by rates of 100 or 200 g CGM per m2, but was reduced by 26% at a rate of 300 g CGM per m2 compared to the control. Differences between studies are likely due to weather conditions (Table 3). The weather was hot and dry during the July 1998 study, warm with rainfall during the August 1999 study, and cool with rainfall during the June 1999 study.

Because of the reduction in seedling survival at even the lowest rate of CGM (100

g m-2), direct seeding into soil into which CGM has been incorporated is not advisable. Transplants may be an alternative to take advantage of the herbicidal effects of CGM and the nitrogen it provides. Broccoli and cauliflower plants were transplanted into soil into which 100, 200, 300, and 400 g CGM per m2 had been incorporated, and had no differences in dry shoot or root weight at 10 and 24 days after transplanting compared to the control (see Appendix 1). Greenhouse studies with strawberry showed no detrimental effects on growth and development of the mother and daughter plants with CGM application (Nonnecke and Christians, 1993). Growers are concerned with a product’s effect on final yield and quality. Future studies should investigate yields of crops transplanted into soil incorporated with CGM.

References

Bingaman, B.R. and N.E. Christians. 1995. Greenhouse screening of corn gluten meal as a natural control product for broadleaf and grass weeds. HortScience 30:1256-1259.

Christians, N.E. 1993. The use of corn gluten meal as a natural preemergence weed control in turf. Intl. Turfgrass Soc. Res. J. 7: 284-290.

Fernandez-Cornejo, J., C. Greene, R. Penn, and D. Newton. 1998. Organic vegetable production in the U.S.: certified growers and their practices. Amer. J. Alternative Ag. 13:69-78.

Fritz, S. 1989. Organic foods and the vegetable industry. Acta Hort. 247: 397-402.

Grubinger, V.P. 1992. Organic vegetable production and how it relates to LISA. HortScience 27: 759-760.

Kelly, W.C. 1990. Minimal use of synthetic fertilizers in vegetable production. HortScience 25: 168-169.

Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of corn gluten meal as a natural, weed control product in strawberry. Acta Hort. 348:315-320.

Peacock, L. and G.A. Norton. 1990. A critical analysis of organic vegetable crop protection in the U.K. Agr. Ecosyst. Environ. 31: 187-197.

SAS Institute. 1996. SAS/STAT guide for personal computers, ver. 6.12. SAS Inst., Inc., Cary, N.C.

Table 1. Percent weed cover at five rates of corn gluten meal (CGM) at termination (July 1998: 19 days after planting (DAP); Aug. 1998: 20 DAP; June 1999: 36 DAP). Values for each study include the following weed species: purslane (Portulaca oleracea L.), common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), ladysthumb (Polygonum persicaria L.), velvetleaf (Abutilon theophrasti Medic.), and foxtail (Setaria spp.).

CGM Percent weed cover (4.1 m2 plot)

(g m-2) July 1998 Aug. 1998 June 1999 Mean

0 80 50 93 78

100 52 20 40 37

200 25 8 23 19

300 18 7 11 12

400 12 6 21 13

LSD(0.05) 25 10 15 11

ANOVA

Source DF Mean Square Pr > F

Study 2 1456.6222 0.0001

Rep(Study) 6 164.2889 0.2091

Corn gluten meal 4 6867.3333 0.0001

Error 32 109.3583

Corrected Total 44

Table 2. Seedling survival of eight vegetable species in three studies using five rates of corn gluten meal (CGM). Percent seedling survival was recorded at 15, 20, and 17 days after planting in July 1998, Aug. 1998 and June 1999 studies, respectively. Values are means of three replications and three studies.

CGM Seedling survival (percent)

(g m-2) Onion Beet Radish Bean Carrot Pea Lettuce Corn Meanx

0 24y 81 69 69 41 70 56 74 60

100 8 53 41 20 11 29 18 67 31

200 3 19 22 12 9 17 9 73 21

300 2 20 16 10 3 12 8 55 16

400 1 7 13 4 0 5 2 48 10

Meanz 7 36 32 23 13 26 19 64

ANOVA

Source DF Mean Square P > F

Study 2 22029.229 0.0001

Rep(Study) 6 389.750 0.0333

Corn gluten meal (CGM) 4 28631.372 0.0001

Study*CGM (Error 1) 8 905.671

Veg 7 13560.497 0.0003

Study*Veg (Error 2) 14 1518.906

CGM*Veg 28 772.567 0.0001

Study*CGM*Veg (Error 3) 56 223.193

Error 234 167.272

Corrected Total 359

z LSD(0.05)=7 for row of means of seedling survival of eight vegetable species.

y LSD(0.05)=10 for interaction means (CGM*Vegetables).

x LSD(0.05)=7 for column of means of seedling survival at five rates of CGM.

Table 3. Percent vegetable seedling survival recorded at 15, 20, and 17 days after planting in July 1998, Aug. 1998 and June 1999 studies, respectively. Corn gluten meal (CGM) was incorporated into the top 2-5 cm of soil before seeds were planted. Values in each study are means of eight vegetables.

CGM Percent survival

(g m-2) July 1998 Aug. 1998 June 1999 Mean

0 45 80 56 60

100 15 53 25 31

200 7 37 18 21

300 4 25 19 16

400 4 16 10 10

LSD(0.05) 7 8 7 5

CHAPTER 4. CORN GLUTEN HYDROLYSATE FOR CRABGRASS CONTROL IN TURF

A paper to be submitted to International Turfgrass Society Research Journal

Melissa C. McDade and Nick E. Christians

Abstract

Concern over the long-term ecological effects of synthetic agricultural chemicals has led to increased efforts in the search for natural weed control products. Corn gluten hydrolysate (CGH) has been identified as a natural preemergence herbicide in greenhouse studies. The objectives of this study were to test humic acid and soybean oil for their capacity to improve the herbicidal and fertilization activity of CGH and to investigate CGH for crabgrass (Digitaria spp.) control in turf in the field. We used CGH at rates of 0, 100, 200, and 400 g m-2, humic acid at 0, 0.93, 1.9, 3.7 and 7.5 ml m-2, and soybean oil at 0, 58, 120, 180, and 230 m l m-2 in greenhouse studies with seeds of perennial ryegrass (Lolium perenne L.). In the field, four rates of CGH (0, 50, 100, and 200 g m-2), humic acid (0, 0.93, 1.9 and 4.1 ml m-2) and soybean oil (0, 59, 120, and 230 m l m-2), were applied to a mature stand of Kentucky bluegrass (Poa pratensis L.). Neither humic acid nor soybean oil affected the performance of CGH in either study. In the greenhouse study, ryegrass seedling survival was decreased by 0, 24, and 65% compared to the control at CGH rates of 100, 200 and 400 g m-2, respectively. In the field study, plots treated with CGH at 200 g m-2 had 69 and 93% fewer crabgrass plants in the 1998 and 1999 studies, respectively, compared to the control. Plots treated with 200 g CGH per m2 had the highest visual quality compared to the control in both field studies. Corn gluten hydrolysate has the potential to be used as a natural weed control and fertilizer product in turfgrass, but its activity is not enhanced by humic acid or soybean oil.

Introduction

Turfgrass areas such as home lawns and golf courses are managed intensively to control pests and satisfy the demands of those who want high-quality turf (Balogh and Anderson, 1992). While many of the chemicals in use are considered safe when used as directed, common pesticides can have unintended consequences, such as harming non-target organisms (Potter et al., 1990), contributing to pesticide resistance (Curtis et al., 1991), and contaminating ground water (Balogh and Anderson, 1992).

Concern over the long-term ecological effects of synthetic agricultural chemicals has led to increased efforts in the search for natural products (Cardellina, 1988). Recently, Gough and Carlstrom (1999) have reported that wheat gluten meal inhibits germination of some weed species in the greenhouse. Earlier studies identified corn gluten meal as a natural, preemergence herbicide for use in turfgrass and other crops (Bingaman and Christians, 1995; Christians, 1993; Nonnecke and Christians, 1993). Corn gluten meal is a by-product of the corn (Zea mays L.) wet-milling process and is used for animal feed. Corn gluten hydrolysate (CGH) is a water-soluble product derived from corn gluten meal.

The CGH is formed by treating an aqueous slurry of corn plant protein with an amylase and then a protease. The resulting filtrate contains CGH and can be evaporated and then spray dried. The dry product of CGH is water soluble (Christians et al., 1994b).

The water-soluble CGH is herbicidally active and contains 10 to 14% N by weight (Christians et al., 1994b; Liu and Christians, 1997; Liu et al., 1994). The CGH acts on germinating seeds. Seedling shoots emerge normally, but the development of the emerging root is inhibited. After a period of water stress, the seedlings wilt and die because they do not have an adequate root system. Five dipeptides and one pentapeptide were isolated from CGH that had inhibitory effects on the root growth of germinating seeds (Christians et al., 1994a; Liu and Christians, 1994; Liu and Christians, 1996). One dipeptide, alaninyl-alanine, was tested and found to cause epidermal necrosis at high concentrations and disruption of cellular processes at lower concentrations in root tissue (Unruh et al., 1997).

Greenhouse tests have shown that CGH has greater herbicidal activity than corn gluten meal (Liu et al., 1994). In a preliminary field trial, however, CGH had varying effects on crabgrass (Digitaria spp.) germination when applied at the same rates as the corn gluten meal (Bingaman and Christians, 1996). These variable effects could be due to rapid microbial degradation or leaching because of the water solubility of the hydrolysate.

Humic acid and soybean oil are carriers that could potentially enhance the activity of CGH in the field. Combinations of herbicides and humic substances caused a reduction in root length in pea (Pisum sativum L.) (Senesi and Loffredo, 1994). Herbicides may be adsorbed by organic matter in the soil (Stevenson, 1994) and humic acid forms complexes with cations in the soil (Olmos et al., 1998), so humic acid may bind with CGH to keep it active in the soil longer and prevent it from leaching. Crop oil concentrates are spray adjuvants which increase the activity of a number of postemergence herbicides (Penner et al., 1983). Soybean oil mixed with herbicides had greater control over certain weeds compared to the control (Kelley et al., 1983; Chaney and Kapusta, 1983), and if used with CGH, could enhance the activity of the CGH.

The 10% N provided by corn gluten meal improves the visual quality of turfgrass (Christians, 1993). Corn gluten hydrolysate contains 10 to 14% N (10% in this study), and likely has a similar fertilizing effect on turfgrass.

The objectives of this study are to determine: 1) whether treatments of humic acid and soybean oil will stabilize the herbicidal and fertilization activity of CGH and 2) what rates of CGH inhibit crabgrass germination in the field.

Materials and Methods

Greenhouse study

Square plastic pots with a surface area of 79 cm2 and a depth of 8.5 cm were filled with 300 g of Nicollet (fine-loamy mixed mesic Aquic Hapludoll) soil that had been screened through a 6.4-mm sieve. Twenty seeds of perennial ryegrass (Lolium perenne L.) were placed 6 mm below the soil surface. The CGH (Grain Processing Corp., Muscatine, Iowa) was weighed at rates equivalent to 0, 100, 200, and 400 g m-2 and dissolved in 20 ml distilled water. Humic acid (RL 37, Liquid Seaweed Foliar, International Ag Labs, Inc., Fairmont, Minn.) at rates of 0, 0.93, 1.9, 3.7 and 7.5 ml m-2, or soybean oil (SprayTech Oil, Agro-K Corporation, Minneapolis, Minn.) at rates of 0, 58, 120, 180, and 230 m l m-2, was added to each rate of CGH for a total of 40 treatments. These 20 ml solutions of CGH and humic acid, or CGH and soybean oil, were pipeted onto the soil surface. The pots were placed on a mist bench in the greenhouse until seedling emergence. They were moved to another bench and watered with distilled water at a rate of 10 ml d-1 for 3 d. Temperature in the greenhouse was maintained in the range of 18 to 27 šC. The pots were allowed to dry for 5 d and then watered once with 10 ml H20. The number of live shoots was counted 3 d later. The experiments were initiated in March 1998 and repeated in November 1998.

Field study

The 2.25-m2 plots were located in a mature stand of ‘Nassau’ Kentucky bluegrass (Poa pratensis L.) at the Horticulture Research Station, 16 km north of Ames, Iowa. The study was initiated in 1998 and repeated in 1999. Treatments were applied 9 May 1998 and 6 May 1999. The CGH was dissolved in 1.5 L of distilled water at rates equivalent to 0, 50, 100, and 200 g m-2. Humic acid at rates of 0, 0.93, 1.9 and 4.1 ml m-2, or soybean oil at rates of 0, 59, 120, and 230 m l m-2 was added to the CGH. The solutions were sprayed onto the plots using a CO2 backpack sprayer with TeeJet no. 8002 flat fan nozzles (TeeJet, Wheaton, Ill.) at a pressure of 376 kPa. The study area was irrigated as needed to prevent dormancy. Weed control was determined by visually estimating the percentage of crabgrass cover throughout the season and counting the number of crabgrass plants at termination on 26 Aug. 1998 and 11 Aug. 1999. Visual quality was based on color, density, and uniformity, and was assessed by using a 9 to 1 scale: 9 = best quality, 6 = lowest acceptable quality, and 1 = poorest quality.

Experimental design and statistics

The greenhouse study had a completely randomized design with three replications in each of the duplicated studies. The field study had a randomized complete block design with three replications per treatment. In both studies, main effects and interactions of the treatments were tested using Fisher’s least significant difference (LSD) test in the general

linear models (GLM) procedure in the Statistical Analysis System (SAS) version 6.12 (SAS Institute, 1996).

Results and Discussion

Greenhouse study

Humic acid and soybean oil had no effect on perennial ryegrass seedling emergence. Seedling survival of perennial ryegrass seeds was reduced by 2, 26, and 63% compared to the control at 100, 200, and 400 g CGH per m2, respectively (Table 1). Liu and Christians (1997) found reductions of 76 and 80% compared to the control at CGH rates of 200 and 400 g m-2, respectively, in a similar greenhouse study. This study confirmed previous results that show CGH acts as a preemergence herbicide in the greenhouse (Liu and Christians, 1997).

Field study

Humic acid and soybean oil had no effect on the number of crabgrass plants or on turfgrass quality in 1998 or 1999 (Tables 2, 3, 4, and 5). There were 69% fewer crabgrass plants at the highest rate of CGH (200 g m-2) compared to the control in the 1998 study (Table 4) and 93% fewer crabgrass plants at the 200-g m-2 rate in the 1999 study (Table 5). Studies with corn gluten meal have shown increased crabgrass control in the second year of a study on the same plot (Bingaman et al., 1998), and CGH likely has a similar effect in the second year of a study. Each increasing rate of CGH improved turfgrass visual quality in the 1998 and 1999 studies (Tables 4 and 5).

The CGH at a rate of 200 g m-2 controlled crabgrass in this study similar to a preliminary field study in which the 200-g m-2 rate reduced crabgrass by 66% compared to the control (Bingaman and Christians, 1996). This reduction is also similar to that evoked by corn gluten meal, which provided 86% control when applied to turf at 200 g m-2 (Christians, 1993). The CGH applied at rates of 50 and 100 g m-2 had varying crabgrass control in this study and varied in effectiveness in a previous study (Bingaman and Christians, 1996). A rate of at least 200 g m-2 may be necessary to control crabgrass in the field.

The CGH used in this study was 10% N by weight, so applying 200 g m-2 provides N at a rate of 20 g m-2. This N fertility was probably responsible for improving the visual quality of the turfgrass at higher rates in the 1998 and 1999 studies (Tables 4 and 5). Other studies have reported this fertilizing effect in both CGH (Bingaman and Christians, 1996) and corn gluten meal (Christians, 1993).

The CGH may not have formed chelates with the humic acid in this study, and could have been degraded at the same rate as the untreated CGH. Because of the agitation needed for proper encapsulation, the soybean oil is not recommended for use with backpack sprayers. Although we agitated the bottles before application, this may not have been effective, and may have affected the performance of the soybean oil in this study. Soybean oil may be an effective carrier for postemergence herbicides, but it showed no increase in weed control with a preemergence herbicide in this or another study (Cantwell and Kapusta, 1984).

This study showed that CGH applied to turf can reduce crabgrass cover and improve turfgrass quality. A long-term study is needed to determine how CGH controls various weeds over time. The CGH is more costly to produce than corn gluten meal, but has the advantage of being water-soluble and sprayable. Other carriers should be investigated to stabilize the activity of CGH. This research will be useful for those who seek to reduce chemical inputs in lawns and for others who research natural products and their potential use in turfgrass.

References

Balogh, J.C. and J.L. Anderson. 1992. Environmental impacts of turfgrass pesticides, p. 221-353. In: J.C. Balogh and W.J. Walker (eds.). Golf course management and construction: environmental issues. Lewis, Chelsea, Mich.

Bingaman, B.R. and N.E. Christians. 1995. Greenhouse screening of corn gluten meal as a natural control product for broadleaf and grass weeds. HortScience 30:1256-1259.

Bingaman, B.R. and N.E. Christians. 1996. 1995 corn gluten hydrolysate weed control study. 1996 Iowa Turfgrass Res. Rpt. Iowa State Univ. Ext., Ames, Iowa.

Bingaman, B.R., N.E. Christians, and M.B. Faust. 1998. 1991 corn gluten meal crabgrass control study &emdash; year 7. 1998 Iowa Turfgrass Res. Rpt. Iowa State Univ. Ext., Ames, Iowa.

Cantwell, J. and G. Kapusta. 1984. Evaluation of soybean oil as a carrier for preemergence soybean herbicides applied with rotary nozzles. North Central Weed Control Conf. Proc. 39:58

Cardellina, J.H., II. 1988. Natural products in the search for new agrochemicals, p. 305-315. In: H.G. Cutler (ed.). Biologically active natural products: potential use in agriculture. Amer. Chem. Soc., Washington, D.C.

Chaney, D. and G. Kapusta. 1983. Evaluation of soybean oil concentrate vs. petroleum oil concentrate with postemergence soybean herbicides. North Central Weed Control Conf. Proc. 38:25.

Christians, N.E. 1993. The use of corn gluten meal as a natural preemergence weed control in turf. Intl. Turfgrass Soc. Res. J. 7: 284-290.

Christians, N.E., J.T. Garbutt, and D. Liu. 1994a. Preemergence weed control using dipeptides from corn gluten hydrolysate. U.S. Patent No. 5,290,757.

Christians, N.E., J.T. Garbutt, and D. Liu. 1994b. Preemergence weed control using plant portein [sic] hydrolysate. U.S. Patent No. 5,290,749.

Curtis, J., L. Mott, and T. Kuhnle. 1991. Harvest of hope: the potential for alternative agriculture to reduce pesticide use. Natural Resources Defense Council, New York.

Gough, R.E. and R. Carlstrom. 1999. Wheat gluten meal inhibits germination and growth of broadleaf and grassy weeds. HortScience 34:269-270.

Kelley, G., W.W. Witt, and C. Slack. 1983. Soybean oil as an additive for broadleaf postemergence herbicides. North Central Weed Control Conf. Proc. 38:17.

Liu, D.L.-Y. and N.E. Christians. 1994. Isolation and identification of root-inhibiting compounds from corn gluten hydrolysate. J. Plant Growth Regul. 13:227-230.

Liu, D.L. and N.E. Christians. 1996. Bioactivity of a pentapeptide isolated from corn gluten hydrolysate on Lolium perenne L. J. Plant Growth Regul. 15:13-17.

Liu, D.L. and N.E. Christians. 1997. Inhibitory activity of corn gluten hydrolysate on monocotyledonous and dicotyledonous species. HortScience 32:243-245.

Liu, D.L.-Y., N.E. Christians, and J.T. Garbutt. 1994. Herbicidal activity of hydrolyzed corn gluten meal on three grass species under controlled environments. J. Plant Growth Regul. 13:221-226.

Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of corn gluten meal as a natural, weed control product in strawberry. Acta Hort. 348:315-320.

Olmos, S., E. Esteban, and J.J. Lucena. 1998. Micronutrient extraction in calcareous soils treated with humic concentrates. J. Plant Nutrition 21:687-697.

Penner, D., F.C. Roggenbuck, and K. Van Fletern. 1983. Rapid evaluation of soybean oil in crop oil concentrates. North Central Weed Control Conf. Proc. 38:124.

Potter, D.A., M.C. Buxton, C.T. Redmond, C.G. Patterson, and A.J. Powell. 1990. Toxicity of pesticides to earthworms (Oligochaeta: Lumbricidae) and effect on thatch degradation in Kentucky bluegrass turf. J. Econ. Entomol. 83:2362-2369.

SAS Institute. 1996. SAS/STAT guide for personal computers, ver. 6.12. SAS Inst., Inc., Cary, N.C.

Senesi, N. and E. Loffredo. 1994. Influence of soil humic substances and herbicides on the growth of pea (Pisum sativum L.). J. Plant Nutrition 17:493-500.

Stevenson, F.J. 1994. Humus chemistry: genesis, composition, reactions. 2nd ed. Wiley, New York.

Unruh, J.B., N.E. Christians, and H.T. Horner. 1997. Herbicidal effects of the dipeptide alaninyl-alanine on perennial ryegrass (Lolium perenne L.) seedlings. Crop Sci. 37:208-212.

Table 1. Greenhouse seedling survival of perennial ryegrass (Lolium perene L.) seeds with treatments of corn gluten hydrolysate. Values are means of humic acid and soybean oil treatments, three replications and two studies.

Corn gluten hydrolysate Seedling survival

(g m-2) (percent)

0 87

100 85

200 64

400 32

LSD(0.05) 6

Table 2. Analysis of variance (ANOVA) for the 1998 study with mean turfgrass visual quality as the dependent variable.

ANOVA

Source DF Mean Square P>F

Rep 2 0.1712963 0.2998

Corn gluten hydrolysate (CGH) 3 16.7710905 0.0001

Rate (of Humic Acid or Soy Oil) 7 0.1889330 0.2405

Rate*CGH 21 0.1382275 0.4861

Error 62 0.1394365

Table 3. Analysis of variance (ANOVA) for the 1999 study with mean turfgrass visual quality as the dependent variable.

ANOVA

Source DF Mean Square P>F

Rep 2 0.0992798 0.4241

Corn gluten hydrolysate (CGH) 3 17.5778464 0.0001

Rate (of Humic Acid or Soy Oil) 7 0.1951793 0.1231

Rate*CGH 21 0.1022438 0.5966

Error 62 0.1141477

Table 4. Turfgrass visual quality and final crabgrass (Digitaria spp.) count at five rates of corn gluten hydrolysate (CGH) for the 1998 season. Mean turfgrass (Poa pratensis L.) quality was rated visually: 9 = highest quality, 6 = acceptable quality, 1 = lowest quality. Crabgrass plants were counted 16 weeks after treatment application on 26 Aug. 1998. Analysis of variance (ANOVA) is shown for crabgrass plants as the dependent variable.

Visual quality Crabgrass

CGH (wks. after treatment) plants

(g m-2) 2 3 4 5 6 7 8 9 10 Mean (no. m-2)

0 5.9 6.1 5.1 5.1 5.5 6.2 6.0 6.6 6.1 5.9 13

50 6.2 6.7 5.5 5.6 6.2 6.8 6.4 6.9 6.3 6.3 8

100 7.3 7.6 6.4 6.5 7.4 7.5 7.0 7.0 6.5 7.0 12

200 7.8 8.7 7.0 8.2 8.5 7.8 7.5 7.3 7.1 7.8 4

LSD(0.05) 0.35 0.29 0.29 0.27 0.44 0.41 0.49 0.42 0.45 0.22 6

ANOVA

Source DF Mean Square P>F

Rep 2 6202.0601 0.0001

Corn gluten hydrolysate (CGH) 3 1998.0363 0.0127

Trt (humic acid or soybean oil) 7 638.1156 0.2903

Trt*CGH 21 393.5627 0.7422

Error 62 510.7803

Table 5. Turfgrass visual quality and final crabgrass (Digitaria spp.) count at five rates of corn gluten hydrolysate (CGH) for the 1999 season. Mean turfgrass (Poa pratensis L.) quality was rated visually: 9 = highest quality, 6 = acceptable quality, 1 = lowest quality. Crabgrass plants were counted 14 weeks after treatment application on 11 Aug. 1999. Analysis of variance (ANOVA) is shown for crabgrass plants as the dependent variable.

Visual quality Crabgrass

CGH (wks. after treatment) plants

(g m-2) 2 3 4 5 6 7 8 9 10 Mean (no. m-2)

0 7.2 5.5 5.8 5.9 5.7 5.8 5.5 6.4 5.6 5.9 14

50 7.4 6.3 6.5 6.5 6.4 6.4 6.1 6.9 6.4 6.5 5

100 7.3 7.3 7.0 7.1 7.0 7.0 6.5 7.2 6.9 7.0 7

200 7.2 8.3 8.3 8.5 8.3 7.5 8.0 7.9 7.8 8.0 1

LSD(0.05) NS 0.30 0.35 0.31 0.40 0.41 0.38 0.40 0.39 0.20 8

ANOVA

Source DF Mean Square P>F

Rep 2 8724.5007 0.0012

Corn gluten hydrolysate (CGH) 3 3581.0371 0.0329

Trt (humic acid or soy oil) 7 895.5999 0.6094

Trt*CGH 21 696.3753 0.9005

Error 62 1153.5336

CHAPTER 5. GENERAL CONCLUSIONS

The previous studies focus on corn gluten meal and corn gluten hydrolysate and their use in turfgrass and other production systems. The results of these studies suggest that corn gluten meal may be used to control weeds in a vegetable transplant system, and that corn gluten hydrolysate may be used to control crabgrass and improve visual quality in turfgrass.

In the first study, all rates of corn gluten meal (CGM) reduced percent weed cover compared to the control. An application rate of 200 g CGM per m2 reduced weed cover compared to the control and greater rates did not significantly increase weed control. Weather conditions affected the studies: seedlings had the lowest survival rate in the July 1998 study, where hot, dry conditions prevailed. Weeds established at a later time in the June 1999 study, which took place during cooler weather. The CGM reduced germination of purslane in greenhouse studies (Bingaman and Christians, 1995), and the results of this study suggest that CGM controls purslane in the field as well. Field studies with strawberry showed weed inhibition with applications of CGM (Nonnecke and Christians, 1993), and the results of this study suggest it may be used for weed control in other production systems as well. Because of the reduction in seedling survival at even the lowest rate of CGM (100

g m-2), direct seeding into soil into which CGM has been incorporated is not advisable. Transplants may be an alternative to take advantage of the herbicidal effects of CGM and the N it provides. There were no differences in broccoli and cauliflower transplants’ dry shoot or root weight at 10 and 24 days after transplanting compared to the control (see Appendix 1). Greenhouse studies with strawberry showed no detrimental effects on growth and development of the mother and daughter plants with CGM application (Nonnecke and Christians, 1993).

In the second study, corn gluten hydrolysate (CGH) at rates of 200 and 400 g m-2 reduced germination of perennial ryegrass seeds in the greenhouse. This study confirmed previous results (Liu and Christians, 1997) that show CGH acts as a preemergence herbicide. In the field study, plots treated with the highest rate of hydrolysate (200 g m-2) had 69% fewer crabgrass plants in 1998 and 93% fewer crabgrass plants in 1999 and the highest visual quality in both years compared to the control. All rates of CGH improved turf quality compared to the control. Humic acid and soybean oil were used in this study to improve and prolong the herbicidal and fertilizing activity of CGH. The results of this study showed neither product had an effect on improving crabgrass control or turf quality. Other products may be tested with CGH in an effort to maintain the higher level of germination inhibition exhibited in greenhouse studies as in the field.

Research on natural products is useful for those who seek to reduce chemical inputs in their lawns or gardens and for others who research natural products and their potential use in turfgrass and other crops. As the demand for organic and natural products grows, research will be needed to develop those products. Future research with corn gluten meal could focus on its effect on final yield and quality of a variety of production crops to evaluate the potential for its use with specific crops. Corn gluten hydrolysate has an advantage with regard to its solubility, and it could be tested with other carriers that may improve its herbicidal activity in the field.

References

Bingaman, B.R. and N.E. Christians. 1995. Greenhouse screening of corn gluten meal as a natural control product for broadleaf and grass weeds. HortScience 30:1256-1259.

Nonnecke, G.R. and N.E. Christians. 1993. Evaluation of corn gluten meal as a natural, weed control product in strawberry. Acta Hort. 348:315-320.

Liu, D.L. and N.E. Christians. 1997. Inhibitory activity of corn gluten hydrolysate on monocotyledonous and dicotyledonous species. HortScience 32:243-245.

APPENDIX 1. ADDITIONAL TABLES

Table 1. Six wk old broccoli (Brassica oleracea L. var. italica L.) and cauliflower (Brassica oleracea L. var. botrytis L.) transplants were planted into soil into which corn gluten meal had been incorporated. Dry shoot weights were recorded on harvested plants at 10 and 24 days after transplanting. Values are means of three replications. Means were separated using Fisher’s least significant difference (LSD) test in the general linear models procedure in SAS.

Corn gluten meal Shoot dry weight (g)

(g m-2) Days after transplanting

10 24

Broccoli Cauliflower Broccoli Cauliflower

0 0.15 0.13 0.94 0.68

100 0.21 0.16 1.19 0.82

200 0.20 0.16 1.36 0.98

300 0.22 0.18 1.12 1.02

400 0.18 0.20 1.02 0.77

LSD (0.05) NS NS NS NS

Table 2. Six wk old broccoli (Brassica oleracea L. var. italica L.) and cauliflower (Brassica oleracea L. var. botrytis L.) transplants were planted into soil into which corn gluten meal had been incorporated. Dry root weights were recorded on harvested plants at 10, 17, and 24 days after transplanting. Values are means of three replications and both vegetables. Means were separated using Fisher’s least significant difference (LSD) test in the general linear models procedure in SAS.

Corn gluten meal Root dry weight (g)

(g m-2) Days after transplanting

10 17 24

Broc. Caul. Broc. Caul. Broc. Caul.

0 0.17 0.16 0.08 0.07 0.18 0.12

100 0.12 0.08 0.10 0.08 0.19 0.12

200 0.17 0.14 0.19 0.08 0.21 0.16

300 0.19 0.16 0.12 0.09 0.19 0.16

400 0.18 0.17 0.11 0.08 0.18 0.13

LSD (0.05) NS NS NS NS NS NS