The objective of this study was to screen Corsair for removal of perennial ryegrass from a ryegrass/creeping bentgrass area maintained at fairway height. This study was conducted at Veenker Golf Course in Ames, IA on the border area between a bentgrass fairway and the adjacent ryegrass/Kentucky bluegrass rough. The bluegrass rough contained approximately 50% ryegrass. The experimental design was a randomized complete block and three replications were conducted. Individual plot size was 5 x 5 ft. The plots were arranged so one half of the plot was covered by bentgrass and the other by bluegrass/ryegrass turf.

Corsair was applied at 1, 2, and 3 oz/A on August 8 using a carbon dioxide backpack sprayer equipped with TeeJet #8006 nozzles at a spray pressure of 30-40 psi. The herbicide was mixed with water to a volume equivalent to 3 gal/1000 ft².

Ryegrass damage was recorded on August 10, August 16 and August 23. Damage was assessed using a 9 to 1 scale with 9 = no damage, 5 = 50% ryegrass mortality, and 1 = 100% ryegrass mortality (Table 1). Phytotoxicity on bentgrass was rated using a 9 to 1 scale with 9 = no damage, 5 = 50% bentgrass damaged, and 1 = 100% bentgrass damaged. Bentgrass damage data were taken from August 10 through October 19 (Table 2). Kentucky bluegrass quality was monitored for possible phytotoxicity from August 10 through October 19 (Table 3). Turf quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality.

Ryegrass control was determined by estimating the percentage cover per individual plot (Table 4). These data were taken initially on August 23 to assess the amount of ryegrass killed. Subsequent cover data were taken to monitor if there was any regrowth.

Percentage cover data were taken for bentgrass to reflect the amount of mortality in the treated plots (Table 5). These data were taken from August 10 through September 19.

The percentage bluegrass/ryegrass cover also was monitored from August 10 through October 19 (Table 6). These figures reflect the spread of bluegrass throughout the areas devoid of ryegrass in the treated plots.

Data were analyzed using the Statistical Analysis System (SAS Institute Inc., 1989-1996) and the Analysis of Variance (ANOVA) procedure. Treatment effects on turf populations and turf quality were examined using Fisher's Least Significant Difference (LSD) test.

There was no damage on ryegrass until approximately 12 days post treatment (Table 1). Yellowing was beginning on August 20 and by August 23, the treated ryegrass was 'brown' and dead. The bluegrass/ryegrass areas of each treated plot were monitored through October 19 and there was no regrowth of ryegrass (Table 4). There were no phytotoxic symptoms on the treated bluegrass (Table 3). Bluegrass spread into the bare areas of the treated plots and by September 28, plots treated with Corsair at 1.0 and 2.0 oz/A were similar to the untreated controls in turfgrass percentage cover (Table 6).

On August 23, significant levels of damage were observed on the treated bentgrass (Table 2). Damage was not significant on bentgrass treated with Corsair at 1 oz/A on August 23 and August 30 as compared with the untreated controls. However, bentgrass treated at 2.0 and 3.0 oz/A exhibited significant levels of damage as compared with the untreated controls on August 23 through September 6. As much as 50% of the bentgrass treated with Corsair at 3.0 oz/A was damaged and suffered severe browning and some mortality. By September 21, the effects of Corsair on percentage cover and bentgrass quality were no longer recorded (Tables 2 and 5). Bentgrass had moved into the bare areas of the treated plots and some of the damaged bentgrass had regrown from the crowns.

This study will be monitored through the spring and summer of 2002 for possible regrowth of perennial ryegrass.

Table 1. Damage on perennial ryegrass¹ treated for the 2001 Riverdale Corsair Ryegrass Control Study.