Perennial ryegrass was evaluated for tolerance to RP EXP31130A (isoxaflutole) herbicide. Two applications were made on 7/8/96 and 8/21/96. After initial applications of RP EXP31130A, the turf was slightly lighter in color at the 0.18 vs. the 0.09 lb. AI/A rate. Enhanced turf color occurred more so for the 0.18 lb. AI/A rate when iron was added, versus the 0.09 lb. AI/A rate. Latent color responses occurred from applications of RP EXP31130A to perennial ryegrass turf. Changes in color were nominal and only discernable when plots were viewed collectively. No phyto-toxicity, leaf scorching, tip burn, bleaching or thinning occurred on perennial ryegrass maintained under the conditions of this test.

Turfgrass mangers select herbicides based on knowledge of efficiency (weed control) and turfgrass tolerance. RP EXP31130A (isoxaflutole) was applied to perennial ryegrass turf (Lolium perenne) in order to assess turfgrass response to this compound at select rates, with and without the addition of iron (as a color enhancer).

A monostand of turf-type perennial ryegrass at the Karsten Turfgrass Facility was used for this test. The turf was mowed 2-3 times weekly at 2.5 inches with a sharp rotary mower and received 3.0 lbs. of nitrogen per 1000 ft² from October 1995 to May 1996. Plots were irrigated to avoid stress. Treatments based on the research protocol were as follows, with all rates of isoxaflutole (hereafter as EXP) expressed in lbs. ai/a. EXP 0.09 lb., EXP 0.18 lb., EXP 0.09 lb + Fe, EXP 0.18 lb. + Fe, EXP 0.36 + Fe, Fe only and the non-treated check. The iron tank mixes were included to determine if it would enhance turf performance, or minimize any potential negative turf response visually. The iron source was Hamp-Iron 845 5% liquid iron, which was applied at the label 1X rate of 0.6 lb. AI/A. The iron in this product is derived from sulfobenzyl glycine.

Plot size was 5'x6'. Applications were made with a hand held three boom nozzle and Co₂ back pack sprayer using 8004 nozzles at 35 psi. This produced a final solution delivery rate of 90 gallons per acre. Each treatment appeared three times in a randomized complete block design. All treatments were applied on July 8, 1996 and again on August 21, 1996.

Turfgrass visual assessments of color, quality and brown patch disease (Rhizoctonia solani) were assigned to plots according to National Turfgrass Evaluation Program (NTEP) and American Society of Pathology standards. Two applications of FORE fungicide were applied to all plots on July 30 and August 28 to suppress foliar symptoms of brown patch. All data were analyzed using SAS software, by the analysis of variance technique. Linear orthogonal polynomial contrasts were devised to compare select product rate and iron combinations. Treatment mean separation was accomplished by calculating Tukey's least significant difference values, only when the F value for treatments was significant at the P=0.05 level or less.

Turfgrass quality mean scores ranged from 5.0 to 6.3, with all EXP treated turfs having mean scores of 5.0 to 5.7. The untreated control and the iron-only treated turf both had mean quality scores of 6.3. Once again, there was no significance for the applied treatment effect at 4 DAT for quality as well (Table 2).

July 18, 1996 (10 DAT/1)
Turfgrass color, quality and percent plot brown patch were assigned values at 10 DAT/1. The applied treatment effect was significant for quality and color, but not for percent plot brown patch.

Mean quality scores ranged from 5.0 to 6.7, with the control and iron-only plots receiving scores of 6.3 and 6.7, respectively. There was no real discernable difference between the rest of the treatments, noting that however, the 0.18 lb. rate of EXP without the iron did score the lowest numerical mean quality value of 5.0 (Table 2).

For perennial ryegrass, turfgrass color treatment means ranged from 5.0 to 7.0 and were statistically significant. The control had slightly better color than the iron-only plot (7.0 vs. 6.7, respectively). EXP at 0.18 lb. without iron had the lowest quality score of 5.0. The addition of iron indirectly helped in the color appearance of the EXP 0.36 lb. treatment (Table 1).

The severity of brown patch reaction of the turf and the % brown patch infestation (0-100%) were non-significant from applied treatments. There was however, a slight trend towards increased expression (severity) when EXP treatments on average were applied. This was generally the case for tall fescue, as well. No conclusions can be drawn from this data set however, regarding disease reaction following application of EXP31130A on ryegrass (Table 2).

August 9, 1996 (32 DAT/1)
The applied treatment effect was not significant one month after treatment, as the mean color scores only ranged from 6.3 to 7.3 (Table 1).

August 23, 1996 (46 DAT/1:2 DAT/2)
Mean color scores ranged from 5.3 to 6.7 and the treatment effect was not significant for turfgrass color on ryegrass at this time. Of interest, is that the EXP 0.18 lb. (without iron) treatment had the best color (6.7). This is perhaps a latent recovery response we often see in turf at 20-30 days after initial treatment with plant protectant chemicals (Table 1).

September 10, 1996 (64 DAT/1:20 DAT/2)
Final color scores were assigned to plots and the applied treatment effect was significant. Mean color scores ranged from 5.0 to 7.0 (slightly sub-standard to above minimum acceptable turf). The EXP 0.18 lb. (no iron) and the iron-only treatment had the largest numerical mean color scores of 7.0 and 6.7, respectively. This again illustrated the latent enhanced color response of the highest EXP rate (without iron) exhibiting a favorable response 2-3 weeks after treatment (Table 1). The EXP 0.36 lb. (with iron) treatment had the lowest color score of 5.0.

The test was concluded at this time.

FN:=rpexp.pr

Table 1. Turfgrass color¹ response of Perennial Ryegrass to applications of RP EXP31130A herbicide. Summer 1996. University of Arizona Karsten Turfgrass Facility.

² Date of evaluation, number of days after respective treatments. Applications made to all treatments on 7/8/96 and again on 8/21/96.

³Chemical treatments of RP EXP31130A, iron, and applicable tank mixes of both.

⁴Rates for EXP31130A in lbs. AI/A. Iron rate of lbs. AI/A, of 5% liquid cheleate. No surfactant added.

⁵Mean of all plots on each evaluation date.

⁶LSD value = Treatment mean separation statistic. Numerical difference between treatments must be larger than the corresponding LSD value for true treatment differences to occur.

Table 2. Mean turfgrass quality, severity and percent plot infection with Brown Patch disease, after applications of RP EXP31130A herbicide. Summer 1996. University of Arizona Karsten Turfgrass Facility.

QUALITY BROWN PATCH EXPRESSION

DATE

DATE

 

TREATMENT4	RATE LB./A5	12 JULY  (10DAT/1)	18 JULY  (10DAT/1)	18 JULY  (10DAT/1)	18 JULY  (10 DAT/1)
EXP 31130A	0.09	5.0	6.0	3.3	14
EXP 31130A	0.18	5.3	5.0	3.3	9
EXP31130A/FE	0.09/0.6	5.3	5.3	4.3	13
EXP31130A/FE	0.18/0.6	5.7	5.3	4.3	7
EXP31130A/FE	0.36/0.6	5.7	6.0	3.3	6
FE-ONLY	0.6	6.3	6.7	2.3	3
CONTROL	--	6.3	6.3	2.3	5
TEST MEAN6		5.7	5.8	3.3	8
LSD VALUE7		NA	0.9	NA	NA

¹Turfgrass quality (1-9), 1 = dead, 9 = best. Values are mean of three replications.

²Severity expression of brown patch disease 1-6, 1 = none, 4 = moderate, 6 = severe. Values are the mean of three replications.

³Percent plot infected with visible brown patch (0%-100%). Values are the mean of three replications.

⁴Treatments of RP EXP31130A, iron and applicable tank mixes. Treatments applied on 7/8/96 and again on 8/21/96.

⁵Rates of RP EXP31130A in lbs. AI/A. Iron applied as lb. AI/A from 5% liquid chelate. No surfactant added.

⁶Mean of all plots on each evaluation date.

⁷LSD value = Treatment mean separation statistic. Numerical difference between treatments must be larger than the corresponding LSD value for true treatment differences to occur.