RP EXP31130A herbicide was applied on two occasions (August 1 and September 4, 1995) to irrigated turf-type tall fescue. Lighter green turf resulted at 8 and 11 DAT. The decrease in color was extremely slight and negligible. No statistical rate response was realized for the decrease in color after one application treatment. The effects were completely gone by 18 DAT. Sequential applications at 0.36 + 0.36 lb. AI/A caused the lightest color turf at 5 days after the second treatment. The overall cumulative effect of the second sequential application showed a decrease in color at 14DAT/2 (not rate dependent however) compared to tall fescue treated once only. All affects were non-detectable by twenty-four days from the second treatment (24DAT/2). EXP31130A had minimal effects on tall fescue causing only a minor color change. No changes in visible density, leaf burn or discoloration were realized at these rates in irrigated tall fescue.

The experimental compound, RP-EXP31130A was tested for turfgrass tolerance under irrigated conditions in the Southwest. Rates and timing applications were evaluated for this new herbicide to assess the potential effects on tall fescue grass. Turf tolerance is an important function as well as efficacy, and tolerance influences the type of turf a herbicide(s) can be safely used on, or if effects are realized, to what extent do they occur and for what length of time. This information is necessary for developing use rates, timing, and product applications in the turfgrass industry.

The material applied to the turf was the 75 WG formulation of RP-EXP31130A. The turf was irrigated with secondary effluent to prevent moisture stress. The turf was mowed two times weekly at 3.0 inches. Based on the above objectives, the RP-EXP31130A herbicide treatments were as applied at the following AI/A rates.

INITIAL APPLICATION SEQUENTIAL APPLICATION

0.18 lb + 0. lb

0.18 lb + 0.18 lb

0.18 lb + 0.36 lb

0.36 lb + 0. lb

0.36 lb + 0.18 lb

0.36 lb + 0.36 lb

All tests included a control. Each treatment appeared four times in a completely randomized block design. Initial and sequential applications were made on August 1 and September 4, 1995, respectively. Materials were applied using a Co₂ compressed air sprayer, using 8004 size nozzles on a three nozzle boom hand held sprayer (20 inch spacing). A total volume of 51 gallons per acre was applied between 500-600 a.m. and watered in within 3 hours after applications via standard turf overhead sprinklers.

The turf was observed for any signs of discoloration, turfgrass damage, or notable changes in density, etc. For this turfgrass species, response observations of turfgrass color were noted throughout the course of development. Observations are noted as days after treatment for each application (response/DAT/N), where N = (1) initial or (2) sequential application. Observation dates are based on expression development, which may have varied in type and number based on the particular turf in question.

Turfgrass color scores were assigned to all plots on five dates after the first application (DAT/1), and on three events after the sequential application (DAT/2) which was made 30 days later. There were no observations of density changes, leaf whitening (indication of loss of chlorophyll) leaf scorching, or visual density loss on tall fescue from EXP31130A.

Effects for herbicide treatments were not significant at 3 DAT/1, but were at 8 and 11 DAT/1 for tall fescue. The effects were no longer discernable at 18 and 28 DAT from the first application (Table 1).

Mean color scores ranged from 6.0 to 6.8 at 3DAT/1, but ranged from 5.8 to 8.0 on 8DAT/1 (Table 1). At 8DAT/1 all EXP treated turf exhibited a slight decrease in color, without leaf yellowing or loss of chlorophyll. The effect was random among treatments, with the 0.18 and 0.16 rates causing the same slight reaction. The color difference was discernable only when viewing the check simultaneously (Table 1). The effects were very minimal and were not objectionable at all in color change for tall fescue. The variety was a three way blend of turf-type tall fescues.

At 11DAT/1, the color scores ranged from 5.5 to 7.3, with the check having only slightly darker color (Table 1). The effects after this were no longer discernable and non-significant at 18 and 28 DAT from the first application. Basically, the effect on tall fescue was a minimal change in overall turfgrass color at 8-11 DAT. There were no changes in visible density, leaf yellowing or loss of chlorophyll (white leaves). There was no rate dependency or response (at those rates tested) for tall fescue (Table 1).

Sequential Application

Color scores were again assigned at 5, 14 and 24 DAT/2. Significant treatment effects occurred at 5 and 14DAT/2, but not at 24DAT/2 from the second series application (Table 2).

The mean color scores ranged from 5.8 to 7.8 at 5 DAT/2. The single application at the 0.18 lb. rate and the check had identical mean color scores of 7.8 (Table 2). The previous single application of 0.36 lb. was next with a mean turf color score of 7.3. The remaining four treatments of the two rate combinations produced color score reductions according to the second rate dosage, as at (0.18), and was close, in rank and cumulative in response for the high (0.36) rate. The lowest mean color score was 5.8 (0.36 + 0.36 treatment), while all other split combinations produced mean color scores of 6.8, showing the same cumulative effect (at 5 DAT/2).

The same general trend occurred at 14 DAT/2, as tall fescue which received only one previous treatment was similar to that of the control, and turfs receiving either repeat combination produced lighter green looking turf. There was no difference however at 14 DAT/2 for (0.18 + 0.18) versus (0.18 + 0.36) treatments. However, the two treatments at 0.36 produced the color results within the same LSD range. At 24 DAT/2, there was no treatment effect, and mean color scores ranged from 6.5 to 7.5, regardless of treatment. This concluded color responses on this test.

FN::RPTACFES.95 DIR:Q495

Table 1. Mean turfgrass color¹ of turf-type tall fescue after applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

Check 6.8 Check 8.0 Check 7.3 .18+.18 6.5 .36+.36 6.8

.36+.18 6.8 .36+.18 6.5 .36+.36 6.3 .36+.36 6.5 .18+.36 6.5

.18+.18 6.5 .18+.36 6.3 .18+.36 5.8 .18+.36 6.0 .18+.18 6.5

.36+0 6.5 .18+.18 6.0 .36+0 5.8 .36+.18 6.0 .36+0 6.5

.36+.36 6.5 .36+.36 6.0 .18+.18 5.8 .18+0 6.0 .18+0 6.3

.18+0 6.3 .36+0 6.0 .18+0 5.8 .36+0 6.0 .36+.18 6.3

.18+.36 6.0 .18+0 5.8 .36+.18 5.5 Check 6.0 Check 6.3

LSD Value⁵ -- LSD Value 0.8 LSD Value 1.1 LSD Value -- LSD Value --

²Rate of product lbs. AI/A

³Number of days after treatment/application number sequence

⁴Mean of all treatments on each test date

⁵LSD Value = least significant difference value. Means with difference greater than LSD statistics are significantly different from each other.

Table 2. Mean turfgrass color¹ of turf-type tall fescue after applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

.18+0 7.8 .18+0 7.0 .18+.36 7.5

Check 7.8 Check 7.0 .36+.18 7.5

.36+0 7.3 .36+0 6.5 Check 7.3

.36+.18 6.8 .18+.36 5.8 .36+0 7.0

.18+.18 6.8 .18+.18 5.5 .18+.18 6.8

.18+.36 6.8 .36+.18 5.0 .36+.36 6.5

.36+.36 5.8 .36+.36 5.5 .18+0 6.5

LSD Value⁵ 0.8 LSD Value 1.3 LSD Value --

²Rate of product lbs. AI/A

³Number of days after treatment/application number sequence

⁴Mean of all treatments on each test date

⁵LSD Value = least significant difference value. Means with difference greater than LSD statistics are significantly different from each other.