RP EXP31130A (isoxaflutole) herbicide was foliar applied to tall fescue turf both with and without iron, in order to determine turfgrass tolerance. Three rates of RP EXP31130A were applied at 0.09, 0.18 and 0.36.lbs. AI/A. The lower two rates were applied both with and without iron (tank mix), while the high rate included iron only. Two applications were made on 7/7/96 and 8/21/96. Applied treatment effects were significant for turfgrass color on 12 July and 12 September. In general, the inclusion of iron provided darker turf which was beneficial when compared to the same rates of RP EXP31130A, without iron. There was on one occasion, damage from iron alone (in August). RP EXP31130A when applied alone caused a slight change in color to tall fescue turf, which was not noticeable to the lay person. No phytotoxicity, leaf tip burn, necrosis, bleaching or thinning of the turf was realized from RP EXP31130A on tall fescue under the conditions of this test.

Turfgrass mangers select herbicides based on knowledge of effective weed control and turfgrass tolerance. RP EXP31130A (isoxaflutole) was applied to tall fescue turf (Festuca aurundinacea) 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 tall fescue 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 3.5 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 non-treated check. The iron tank mixes were included to determine if inclusion would enhance turf performance, or minimize any potential negative turf response visually. The iron source was Hamp-iron 845 (5%), applied at the label rate of 0.6 lb. AI/A. The cheleating agent is derived from sulfo benzyl glycine.

Plot size was 5'x6'. Applications were made with a hand held three boom nozzle with a Co₂ back pack sprayer using 8004 nozzles at 35 psi. This provided 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 7, 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 25 and August 30 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 using Tukey's least significant difference values, only when the F value for treatments was significant at the P=0.05 level or less.

July 12, 1996 (5 DAT/1)
Mean turfgrass quality scores varied from 5.3 to 7.0 at 5 DAT for quality (Table 2), and from 4.7 to 6.7 for turfgrass color (Table 2). Turf treated with iron only had the highest numerical color score of 6.7, followed by the tank mix of the lowest rate of herbicide (0.09 lb/Fe). There was a subtle difference between the 0.18 and 0.36 lb. rates of EXP with the Fe additions. The 0.18 lb. alone (highest application rate without iron) had the lowest mean color score (4.7). The turf exhibited an overall color change, but did not exhibit any severe discoloration, tip burn, or loss of chlorophyll (Table 1).

Overall turfgrass quality was more variable and three treatments showed mean values of 6.0 or greater. These included EXP 0.09 lb./Fe, Fe alone, EXP 0.36 + Fe. It should be noted that summer desert conditions for tall fescue are the most difficult for maintaining a cool season grass year round (Table2).

July 19, 1996 (12 DAT/1)
Color and quality scores were not significant due to treatments at 12 DAT. Mean color scores ranged from 5.3 (control plots) to 7.0 for the iron plots only. The EXP 0.18 lb. treatment had an identical mean score as that of EXP 0.36 lb./Fe plots (5.7). The control had the lowest numerical mean score of 5.3. Although non-significant statistically, the turf seemed to respond with slightly enhanced color from both the addition of iron in the respective tank mixes. as well as from a small latent response from EXP alone. This is after a typical response after applications of many plant protectant chemicals (Table 1).

August 9, 1996 (33 DAT/1)
Color alone was assigned to plots on this date. Quality was not assigned due to the onset of brown patch disease. Mean color scores ranged from 5.3 to 6.0, with no significant treatment effect (Table 1).

The second application (all treatments) was made on August 21, 1996.

August 23, 1996 (47 DAT/1:2 DAT/2)
Turfgrass color and quality scores were assigned to plots and there was no significant difference due to treatments. Color scores ranged from 4.7 to 6.0. The EXP 0.09 lb. treatment had the highest numerical mean color score (6.0). The high rate of EXP (0.36/Fe) had the lowest numerical mean color score (4.7) (Table 1). Quality scores (non-significant) ranged from 4.7 to 6.0. It was interesting to note that the iron-only treated tall fescue had the lowest quality as the turf did not respond favorably to the application of the iron alone. Iron applications can cause some discoloration to cool season turfgrasses when under heat stress (Table 2).

This trend was slightly evident with the application of iron to the two EXP rates of 0.09 lbs. and 0.18 lbs. At this time the iron tank mixes had equal or lower quality scores than the EXP alone, at both respective rates. These differences were subtly and not statistically significant, however (Table 2).

August 28, 1996 (52 DAT/1:7 DAT/2)
Turfgrass color response was significant due to treatments, but overall quality was not. Mean color scores ranged from 4.0 to 7.3. EXP at the 0.18 lb. rate had the lowest mean color score of 4.0. With the addition of iron, the same treatment (EXP 0.18 lb./Fe) had an elevated mean color score of 6.3 (Table 1).

Both the low and medium rates of EXP had acceptable mean color scores of 6.3, or greater, with the addition of iron. Without the iron, color performance decreased, especially at the 0.18 lb. rate of EXP, which had less color intensity than the EXP 0.36 lb./Fe treated turf (mean color = 5.3). The iron-only plots had the highest numerical mean color (7.3) (Table 1).

Overall turfgrass quality scores ranged from 4.3 (non-treated control) to 6.3 (EXP 0.09 lb./Fe). Although non-significant statistically, the mean turfgrass quality scores for the EXP 0.18 lb. and non-treated (control) turf had the lowest quality turf based on visual estimates (4.7 and 4.3, respectively). This was "hard times" for tall fescue in general, however (Table 2).

September 12, 1996 (67 DAT/1:22 DAT/2)
Turfgrass color scores were assigned as well as visual estimates of the amount of turf previously infected with the brown patch fungus. The treatment effect was significant for turfgrass color, but not for brown patch.

Mean color scores ranged from 4.3 to 7.3, as EXP treated turf (no-iron added) exhibited the lowest overall color scores (4.3 to 4.7). The addition of iron as a tank mix to EXP increased color noticeably, as color scores ranged from 6.0 to 7.3 among EXP/Fe treatments (Table 1). Once again, turf which received the herbicide responded with latent enhanced color, which were similar, or slightly greater than the iron-only treatment. This was evident as the EXP 0.18 lb./Fe and EXP 0.36 lb./Fe treatments had turfgrass mean color scores of 7.3 and 6.3, respectively. EXP treated turf at the 0.09 and 0.18 lb. rates had mean turf color values slightly less than the non-treated control. The linear orthogonal contrast for "Fe alone vs. EXP with Fe" among EXP treated turf was significant on this date. This showed that the latent turfgrass color response plus iron (tank mix) did enhance turfgrass color over just the iron-alone treatment. This was also true on the previous evaluation date as well (Table 1).

Finally, there was no significant treatment effect for percent brown patch, which was assigned as the percent dead turfgrass on a plot basis (0-100%). Mean scores ranged from 2 to 12%. It was interesting to observe that the highest rate of EXP with iron (0.36 lb./Fe) had the highest mean infection percentage. This again was non-significant statistically (Table 2).

No phytotoxicity, leaf tip burn, necrosis, bleaching or thinning of the turf was realized from RP EXP31130A on tall fescue, under the conditions of this test.

FN:RPEXPTF.96 DIR:Q496

Table 1. Mean tall fescue color scores¹ after applications of RP EXP31130A herbicide. Summer 1996. University of Arizona Karsten Turfgrass Facility.

² Date of evaluation followed by number of days after treatment (DAT) for respective applications.

³Treatments applied as foliar applications on 7/7/96 and again on 8/21/96.

⁴Rates for EXP31130A in lbs. AI/A. Iron applications in lbs. AI/A from 5% Fe liquid cheleate. No surfactant added.

⁵Mean of all plots.

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 quality¹ and percent brown patch disease injury of Tall Fescue turf after applications of RP EXP31130A. Summer 1996. University of Arizona Karsten Turfgrass Facility.

² Date of evaluation followed by number of days after treatment (DAT) for respective applications.

³Treatments applied as foliar applications on 7/7/96 and again on 8/21/96.

⁴Rates for EXP31130A in lbs. AI/A. Iron applications in lbs. AI/A from 5% Fe liquid cheleate. No surfactant added.

⁵Mean of all plots.

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