RP EXP31130A herbicide was applied on two occasions at 0.18 + 0.36 lbs. AI/A on 'Penncross' creeping bentgrass turf during the summer of 1995. Creeping bentgrass quickly developed the symptoms of bleaching (white leaves-loss of chlorophyll). From the initial application, the degree and extent of bleaching was rate dependent, with maximum expression at 9-10 days after treatment (DAT). After a second treatment of these rate combinations one month later, bleaching was generally a linear and cumulative response. After bleaching occurred, the turf turned straw (necrotic in color), but generally showed regrowth, except for some plots at the high (0.36 lb. AI/A) rate. Sequential treatments caused overall color loss of turf as well at both 5DAT/2 and 14DAT/2. Turfgrass color was restored 7-8 weeks after treatment from single initial applications at either rate, however, the turf did not tolerate sequential applications, and was visibly damaged for 30 days from the sequential treatment. At 25DAT/2 loss of turf occurred on treatments which received at least one application at the 0.36 lb. AI/A rate, and as well as from any sequential combination. The tolerance of 'Penncross' creeping bentgrass is very low to RP EXP31130A.

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 Penncross creeping bentgrass. 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 six times weekly at 0.1565 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 3 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 leaf bleaching, turfgrass color, quality, percent plot chlorosis, and percent live turf 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.

For creeping bentgrass, various symptoms and turf responses developed throughout the response period. These included initial leaf whitening, necrosis thinning, and various degrees of regrowth. Measured responses were significant on all evaluation dates, for both initial and sequential application periods.

The first symptom for 'Penncross' creeping bentgrass was bleaching of the leaf (chlorophyll degradation). Percent of the plots which showed bleaching ranged from 0% from the check, to 54% for the turf at the high (0.36 lb.) rate (Table 1). Mean bleaching ranged from 27% to 30% among the three treatments which received the low rate (0.18 lb. AI/A). The linear contrast for rate was significant at 6 DAT/1 for leaf bleaching.

Three days later at 9 DAT/1, symptoms intensified proportionately. Leaf bleaching ranged from 16% to 81-90% for the 0.36 lb. treatments. The 0.18 lb. rate was not far behind with 77-80% bleaching at 9 DAT/1. The check showed some bleaching (Table 1). It is not known if the herbicide moved laterally within the sand green.

At 15 DAT/1, necrosis had developed and plots were evaluated for the percent plot necrosis (0-100%) based on leaf symptomology. Treated turf ranged from 10-40% leaf straw (Table 2). The linear contrast for the rate effect was significant as the higher rate produced more necrosis than the low rate. No chlorosis was realized on the check.

Overall turfgrass quality scores were assigned to all plots at 15 DAT/1. Treated plots produced poor quality creeping bentgrass, with scores ranging from 3.0 to 4.5 (Table 3). Turf which received the 0.36 lb. rate was most unacceptable, while the 0.18 lb. rate produced turf with near quality scores of 4.5 (moderately poor turf). The check turf scored a mean value of 8.0.

The remaining bleached turf was rated again at 15 DAT/1. Treated turf ranged from 5% to 11% bleaching. However, note that a considerable amount of necrosis was evident, as described above previously (Table 1).

At 25 DAT/1, percent plot chlorosis (straw colored turf), and percent green cover and overall quality scores were assigned.

Percent plot necrosis ranged from 4% to 28% among EXP 31130A treated bentgrass at 25 DAT/1 (Table 2). Rate effects for EXP treated turf were not significant, however the higher rate did produce more (but variable) necrotic turf. Percent plot green (0-100%) ranged from 75% to 99% for treated turf. Recovery was higher for the low rate (0.18 lb.) bentgrass, then for the high rate (0.36 lb.) on average. A 10% effect is quite noticeable on creeping bentgrass maintained as a green. This was reflected in overall turf quality at 25 DAT/1 (Table 3). Two of the three treatments which received the initial 0.18 lb. rate had borderline acceptable quality mean scores of 5.0 - 5.5. Turf treated at 0.36 was visibly unacceptable.

The sequential applications were made on September 4, 1995.

At 5 DAT/2, turfgrass color, and percent plot bleaching were assigned to plots. Mean bleaching scores ranged from 0% to 16%. The sequential treatment(s) caused the same amount of bleaching (no linear rate effect) at 5 DAT/2. It was noted that those treatments receiving no sequential applications (0.18+0) and (0.36+0) had no leaf bleaching remaining (Table 1).

Turfgrass color changes were noticed at (5 DAT/2) after the second application. Rate effects were not significant as all sequential combinations resulted in very poor color turf (mean color scores of 2.8-3.0). Those treatments receiving only the initial single application had turf scores identical to that of the control (mean = 6.0) (Table 3).

At 14 DAT/2, the percent plot bleaching increased in intensity over 5 DAT/2. Bleaching scores ranged from 23% - 51%. There was no significant rate effect however, as both rates applied twice in factorial design produced variable, but damaging results (Table 1).

Final scores for turfgrass color and percent green turf were made at 25 DAT/2 on September 30, 1995. Mean color scores ranged from 4.3 to 7.5. Sequential treatments on bentgrass had marginal to poor color, with mean color scores ranging from 4.3 to 5.5 (Table 3). This turf would be of lesser acceptable turf color to the average golfer. Turf treated 50 days earlier once (at either rate) had turf color scores identical or greater than the check.

The percent green turf (% living ground cover) however was dramatically affected by sequential treatments, regardless of rate combinations. Turf treated twice ranged from 38% - 68% live turf, which was easily recognized as severely damage bentgrass turf (Table 2). Close inspection of the turf showed that the one time single application at 0.18 lb. (low rate) was equal to that of the check (100%), while the one time single application at the high rate (0.36 lb. AI/A) produced turf with 91% cover. Although this was statistically identical to the check and the single 0.18 treatment, it was a noticeable loss of turf on bentgrass (9% loss).

FN:RPPEN.95 DIR:Q495

Table 1. Percent plot bleaching¹ of Penncross creeping bentgrass following applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

RATE2	6DAT/13	RATE	9DAT/1	RATE	15DAT/1	RATE	5DAT/2	RATE	14DAT/2
.36+.18	54	.36+.18	90	.36+.18	11	.18+.36	16	.36+.18	51
.36+0	54	.36+.36	85	.18+0	8	.18+.18	15	.18+.36	35
.36+.36	43	.36+0	81	.36+0	8	.36+.36	15	.36+.36	28
.18+.36	30	.18+0	80	.18+.18	6	.36+.18	15	.18+.18	23
.18+0	29	.18+.18	78	.36+.36	6	.18+0	0	.36+0	0
.18+.18	27	.18+.36	77	.18+.36	5	.36+0	0	.18+0	0
check	0	check	16	check	0	check	0	check	0
Test Mean4	33	Test Mean	72	Test Mean	6	Test Mean	9	Test Mean	21
LSD Value5	11	LSD Value	25	LSD Value	5	LSD Value	5	LSD Value	19

¹Percent plot bleaching (0-100%) loss of chlorophyll - leaf whitening. Values are mean of four replications.

²Rates referred to in lbs. AI/A.

³DAT/N = number of days after treatment and application sequence, respectively.

⁴Mean of all treatments on each evaluation date.

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

Table 2. Percent plot necrosis¹ (straw turf) response and percent final living ground² cover of Penncross creeping bentgrass after applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

------% PLOT NECROSIS------

FINAL % LIVE TURF

RATE3	15DAT/14	RATE	25DAT/1	RATE	25DAT/2
.36+.18	40	.36+.18	28	.18+0	100
.36+.36	25	.18+.18	13	check	100
.36+0	24	.36+.36	12	.36+0	91
.18+.18	20	.36+0	9	.18+.18	68
.18+.36	13	.18+0	4	.36+.36	57
.18+0	10	.18+.36	4	.18+.36	39
check	0	check	0	.36+.18	38
Test Mean5	19	Test Mean	10	Test Mean	70
LSD Value6	12	LSD Value	12	LSD Value	30

¹Percent plot necrosis (0-100%) = straw turf cover. Values are means of four replications.

²Percent final ground cover alive at 25DAT/2 (0-100%).

³Rates referred to in lbs. AI/A.

⁴DAT/N = number of days after treatment and application sequence, respectively.

⁵Mean of all treatments on test date.

⁶LSD Value = least significant difference value. Means with difference greater than LSD statistics are significantly different from each other.

Table 3. Mean color¹ and turfgrass quality² scores of Penncross creeping bentgrass following applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

------QUALITY------

------COLOR------

RATE3	15DAT/14	RATE	25DAT/1	RATE	5DAT/2	RATE	14DAT/2	RATE	25DAT/2
check	8	check	6.8	.18+0	6.0	.18+0	6.0	.18+0	7.5
.18+.36	4.5	.18+0	5.5	.36+0	6.0	.36+0	6.0	.36+0	7.3
.18+.18	4.5	.18+.36	5.0	check	6.0	check	6.0	check	7.3
.18+0	4.5	.36+0	4.5	.36+.18	3.0	.36+.18	3.3	.18+.18	5.5
.36+.36	3.8	.18+.18	4.3	.18+.18	2.8	.36+.36	3.3	.36+.36	5.3
.36+0	3.3	.36+.36	4.3	.18+.36	2.8	.18+.18	3.0	.18+.36	4.8
.36+.18	3.0	.36+.18	3.0	.36+.36	2.8	.18+.36	2.8	.36+.18	4.3
Test Mean5	4.5	Test Mean	4.8	Test Mean	4.2	Test Mean	4.3	Test Mean	6.0
LSD Value6	1.1	LSD Value	2.0	LSD Value	0.4	LSD Value	0.8	LSD Value	1.1

¹Color scores (1-9). 1 = straw, 9 = dark green. Values are mean of four replications.

²Quality score (1-9). 1 = dead turf, 9 = best. Values are mean of four replications.

³Rates referred to in lbs. AI/A.

⁴DAT/N = number of days after treatment and application sequence, respectively.

⁵Mean of all treatments on each evaluation date.

⁶LSD Value = least significant difference value. Means with difference greater than LSD statistics are significantly different from each other.