1999 Iowa Turfgrass Research Report

Prograss (ethofumasate) is an herbicide that has been shown to selectively remove Poa annua from perennial ryegrass on golf course fairways. It is a postemergence material but also has some preemergence effects on susceptible species. While Prograss has been shown to be safe for use on perennial ryegrass, its usefulness on Kentucky bluegrass and creeping bentgrass fairways is less certain and there is a risk of damage to these species at higher rates of application.

Primo (trinexapath-ethyl) is a GA (gibberellic acid) inhibiting compound that is used as a growth retardant on golf course fairways. It has been promoted as both a prestress conditioning product to help Poa annua survive the stress conditions in summer and as a potential method of reducing Poa annua population in creeping bentgrass fairways.

The objectives of the 1998 Poa annua control studies were to observe the effects of Prograss and Primo on Poa annua populations in golf course fairways and to observe the effects of these compounds on a variety of species under controlled conditions at the Iowa State University turfgrass research area.

The treatments listed in Table 1 were applied to the fairway plots monthly from May through November and data on Poa annua survival were taken in November of 1998. The plots were also observed through the season for any signs of damage from the treatments.

The studies were conducted on the following sites:

1. The 16^th fairway at Otter Creek Golf Course in Ankeny, Iowa, which is located in the central part of the state. Species: Kentucky bluegrass, with 10 to 20% Poa annua.

    

2. The 13^th fairway at Hyperion Country Club in Johnston, Iowa, also in central Iowa. Species: Creeping bentgrass (Penneagle) fairway with 55 to 70% Poa annua.
    

   3. The 5^th fairway (15^th fairway for small plots) at Fort Dodge Country Club, Fort Dodge, Iowa, located in the northern and western part of the state. Perennial ryegrass/Kentucky bluegrass fairway (originally seeded to Fylking, Park and common) with 45 to 70% Poa annua.

There were two treated areas at each site. Large plots that measured 5 ft. wide and extended the full width of the fairway received treatments 1-10 (Table 1) monthly from May through November. The treatments were applied by course personnel with fairway sprayers that had only one boom section active.

A small plot area was also established on fairways at each course. These plots measured 3 x 5 ft. and all 11 treatments (Table 1) were applied in 3 replications. These treatments were applied monthly with a small plot sprayer by Steve Krantz of D&K Turf Products in Des Moines and myself, with help from Steve Davis of AgrEvo.

Data were collected on percentage Poa annua population at initiation of treatments in May of 1998 and at the end of the season in November. An analysis of variance was conducted on percentage Poa annua reduction in each plot. The treated plots were also observed on a regular basis for any signs of phytotoxicity (damage) from the treatments.

The results of treatments at each site are listed in Table 1. Notice that on the line marked LSD 0.05, NS means nonsignificant. Even though there appears to be treatment differences, these differences are due to chance because of the high degree of variability among replications. Where a number occurs in this line, such as the 17 under the Fort Dodge Fairway column, there are real differences among treatments. In this case, any treatment responses that are at least 17 units apart are considered to be significantly different. The study was very successful at Fort Dodge Country Club and significant reductions of Poa annua were observed in response to several treatments. Otter Creek treatments on large plots were also effective in several cases. No treatment effects were observed at the end of the season at Hyperion and no data are listed for November, 1998 observations. In the spring of 1999, however, significant reductions in annual bluegrass were observed on plots treated with higher rates of Prograss.

Small plot treatments were also very effective at Fort Dodge Country Club. Because of mid-season flooding on the small plots at Otter Creek, there were no significant treatment effects. Small plots at Hyperion actually showed an increase in Poa annua populations in several treatments. The reason for this response is unknown.

At no times during the season were there any signs of phytotoxicity on any of the plots at the three golf courses.

Table 1. Percentage reduction in Poa annua in response to Prograss and Primo, 1998.

Treatment	Rate/1000 ft2	Ft. Dodge Fairway, Fall-98	Ft. Dodge Fairway, Spring-99	Ft. Dodge Small Plot	Otter Creek Fairway, Fall-98	Otter Creek Fairway, Spring-99	Otter Creek Small Plot	Hyperion Fairway, Spring-99	Hyperion Small Plot, Fall-98
1. Control	0	17	22	14	0	5	39	0	9
2. Prograss EC+Sprint 330+46-0-0	.75 oz + 7.34 oz + .54 lb	19	38	60	14	79	62	3	+39
3. Prograss EC+Sprint 330+46-0-0	1.5 oz + 7.34 oz + .54 lb	53	74	82	0	35	73	18	+64
4. Primo EC+Sprint 330+46-0-0	.25 oz + 7.34 oz + .54 lb	11	22	14	39	24	60	5	0
5. Primo EC+Sprint 330+46-0-0	.5 oz + 7.34 oz + .54 lb	14	24	20	32	60	58	3	+26
6. Prograss EC+Sprint 330+46-0-0	.25 oz + 7.34 oz + .54 lb	13	17	17	6	13	49	5	+42
7. Prograss+Primo Sprint 330+46-0-0	.25 oz +.25 oz + 7.34 oz + .54 lb	15	24	11	7	63	55	10	+14
8. Prograss+Primo Sprint 330+46-0-0	.75 oz +.25 oz + 7.34oz + .54 lb	24	30	58	49	42	54	0	+55
9. Prograss+Primo Sprint 330+46-0-0	1.5 oz +.25 oz + 7.34 oz + .54 lb	60	90	79	54	95	69	38	+116
10. Sprint 330 + 46-0-0	7.34 oz + .54 lb	19	19	28	19	36	46	3	+11
11. Prograss Alone	1.5 oz			28			45		+12
LSD 0.05		17	4	21	33	47	NS	12	58

There were no reductions in quality of fairway grasses at any of the sites during the season.

ISU Horticulture:Publications:1999 Turfgrass Report

College of Agriculture