1999 Iowa Turfgrass Research Report

The growth regulator, Trinexapac-ethyl (Primo), was screened for effects on the establishment of 'Majestic' Kentucky bluegrass sod. This study was conducted at the Iowa State University Horticulture Research Station north of Ames, Iowa in a 'Majestic' Kentucky bluegrass area where a similar sod study was conducted in 1996. The sod was cut in the opposite direction as the previous study to offset any possible carryover effects. The soil in this area was a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with 4.5% organic matter, a pH of 7.12, 4 ppm P, and 93 ppm K.

Rainfall was sporadic throughout the duration of this study. Supplemental irrigation was used to maintain the bluegrass in good growing condition and to facilitate sod root development.

Individual plots were 5 x 5 ft and four replications were conducted. There were six Primo treatment regimes and an untreated control. All Primo applications were made at the label rate for Kentucky bluegrass (0.75 fl oz/1000 ft²). The timing of applications was in reference to sod cutting and establishment. The treatments included an application of Primo six and two weeks before sod establishment, two and six weeks after, two weeks before, two weeks after, six and two weeks before plus two and six weeks after, and two weeks before plus two weeks after (Table 1).

Primo 1EC was applied at 30 psi with a carbon dioxide powered backpack sprayer equipped with Teejet® #8006 flat fan nozzles. The Primo was mixed in 283 ml of water which translates to an application rate of 3 gal/1000 ft².

The six weeks before sod establishment treatments were applied on June 10, 1998 and the two weeks before were made on July 9. The two weeks after treatments were applied on August 5 and the six weeks after sod establishment treatments were made on September 2.

The bluegrass on the entire experimental plot was cut on July 23 using an 18-inch sod cutter. Within each individual plot, sod pieces were cut that matched the outside diameter of 12 x 12 in wooden frames that were constructed with bottoms of 18 mesh screen. The pieces were trimmed and transplanted into the frames and the frames with the sod pieces were returned to the holes and placed flush with the soil surface. There were four frames per individual plot, one in each of four quadrants. The study was watered thoroughly upon completion and was watered on a regular basis to prevent the sod from drying.

Root development was measured using a hydraulic sod pulling apparatus equipped with steel cables that could be attached to screw hooks on the corners of wooden frames (Figure 1). The tensile strength required to 'pull' a frame from the soil was measured in pounds per square inch (psi). One frame per plot was sampled on each of four collection dates beginning on August 4, two weeks after sod establishment. The other frames were harvested at two-week intervals on August 18, September 2, and September 16 (Table 4).

Visual quality data were taken on a weekly basis from June 16 through September 16 (Tables 2 and 3). Visual quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality.

Data were analyzed using the Statistical Analysis System (SAS, Version 6.12) and the Analysis of Variance (ANOVA) procedure. Means were compared with Fisher's Least Significant Difference (LSD) means separation test.

On June 24 and July 17, numerical differences in visual quality were found. The Primo treated plots showed a slight phytotoxicity on June 24, two weeks after treatment. On July 17, the bluegrass that was treated on both June 10 and July 9 (treatments 2 and 6) had a better color than the other treated and untreated turf. The bluegrass treated on July 9 only (treatments 4 and 7) showed a slight phytotoxicity. The phytotoxicity was not detectable after a few days. There were no differences in turf quality after July 17 (Table 2).

There were numerical tensile strength differences in sod harvested on August 4, August 18, and September 2 but the treatment effects were not statistically different (Table 4). On September 16, the sod treated with Primo 1EC two weeks before establishment had significantly more root development than sod treated two and six weeks before, two weeks before and after, sod treated two and six weeks after, and the untreated control. Root development was similar for sod treated six and two weeks before and two and six weeks after establishment and sod treated two weeks after establishment. The data from September 16 show that root tensile strength was 30% higher for sod treated with Primo 1EC two weeks before establishment than for untreated sod.

Table 1. Timing of Primo applications for the 1998 Sod Establishment Study

			Timing of applications*
	Material	Rate /plot	6 weeks before	2 weeks before	2 weeks after	6 weeks after
1	Untreated control	NA	NA	NA	NA	NA
2	Primo 1EC	0.75 oz	yes	yes	no	no
3	Primo 1EC	0.75 oz	no	no	yes	yes
4	Primo 1EC	0.75 oz	no	yes	no	no
5	Primo 1EC	0.75 oz	no	no	yes	no
6	Primo 1EC	0.75 oz	yes	yes	yes	yes
7	Primo 1EC	0.75 oz	no	yes	yes	no

*Timing is in reference to cutting of sod. Six and two weeks before cutting and two and six weeks after establishment. Sod Harvested on July 23. Six weeks before harvest applications made June 10, 2 weeks before on July 9, 2 weeks after on August 5, and 6 weeks after on September 2.

Frames were pulled on August 4, August 18, September 2, and September 16.

Table 2. Visual quality¹ of Kentucky bluegrass in the 1998 Sod Establishment Study (June 16 - August 4).

	Material	June 16	June 24	June 30	July 7	July 17	July 29	August 4
1	Untreated control	8.0	8.0	7.0	7.0	6.3	7.0	7.0
2	Primo 1EC	8.0	5.0	7.0	7.0	7.5	7.0	7.0
3	Primo 1EC	8.0	8.0	7.0	7.0	6.3	7.0	7.0
4	Primo 1EC	8.0	6.0	7.0	7.0	6.0	7.0	7.0
5	Primo 1EC	8.0	8.0	7.0	7.0	6.5	7.0	7.0
6	Primo 1EC	8.0	5.0	7.0	7.0	6.8	7.0	7.0
7	Primo 1EC	8.0	8.0	7.0	7.0	6.0	7.0	7.0
	LSD0.05	--	NS	--	--	NS	--	--

¹Visual quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality.

NS = means are not significantly different at the 0.05 level.

-- = means comparison tests are not applicable to these data.

Table 3. Visual quality¹ of Kentucky bluegrass in the 1998 Sod Establishment Study (August 11 - September 16).

	Material	August 11	August 18	August 26	Sept 2	Sept 9	Sept 16	Mean quality
1	Untreated control	7.0	7.0	7.0	8.0	8.0	9.0	7.4
2	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.3
3	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.4
4	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.2
5	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.4
6	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.2
7	Primo 1EC	7.0	7.0	7.0	8.0	8.0	9.0	7.4
	LSD0.05	-	-	-	-	-	-	0.1

¹Visual quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality.

NS = means are not significantly different at the 0.05 level.

-- = means comparison tests are not applicable to these data.

 

Table 4. Root tensile strength and knitting of Kentucky bluegrass sod growing in frames in the 1998 Sod Establishment Study as measured by the number of pounds per square inch (psi) to pull 1 ft² frames.

	Material	August 4	August 18	September 2	September 16	Mean strength
		________________________________ psi ________________________________
1	Untreated control	57.5	252.5	385.0	355.0	262.5
2	Primo 1EC	37.5	285.0	395.0	385.0	275.6
3	Primo 1EC	53.8	270.0	300.0	382.5	251.6
4	Primo 1EC	18.8	298.8	346.3	460.0	280.9
5	Primo 1EC	23.8	272.5	341.3	401.3	259.7
6	Primo 1EC	35.0	315.0	331.3	415.0	274.1
7	Primo 1EC	33.8	243.8	346.3	395.0	254.7
	LSD0.05	NS	NS	NS	63.0 P > F = 0.07	NS

NS = means are not significantly different at the 0.05 level.

Frames were pulled on August 4, August 18, September 2, and September 16.

Figure 1. The hydraulic sod pulling device used to measure root tensile strength of the sod in the 1998 Sod Establishment Study.

ISU Horticulture:Publications:1999 Turfgrass Report

College of Agriculture