Purpose

The purpose of this trial was to evaluate a potassium salt formulation of Roundup as compared to IPA and diammonium salt formulations for control of cool season turfgrass species.

Materials and Methods

The trial was initiated at the Lewis-Brown Horticulture Farm in Corvallis, Oregon on August 5, 2008. The GPS coordinates for this site are N 44o 32’ 59.33” and W -123o 12’55.53”. The site consisted of a mix of annual bluegrass and bentgrass with small amounts of perennial ryegrass and tall fescue growing on soil. Two broadleaf weeds, white clover and yarrow, were present in small amounts.

The soil consisted of a silty clay loam with a pH near 6.0. Before the trial started, the site was irrigated every other day with an automated weather based system at 80% of ET using RainBird 5000 landscape heads. Irrigation was not applied the night after the treatments but was resumed thereafter. Nitrogen applications had previously been made when needed to keep the turf healthy but not excessively green. The site was mowed two times per week with a rotary mower with clippings returned.

The treatments were applied with a CO2 sprayer with a 5 foot boom spraying 2 gallons per 1,000 square feet at 30 psi using TeeJet 80015 flat fan nozzles.

Visual ratings of percent control were taken 3, 5, 7, 15, 24, and 36 days after treatment. Early ratings should be interpreted as percent injury as death had not occurred. The data for each rating date were subjected to analysis of variance (ANOVA) with differences between means determined by LSD at the five percent level.

The treatments applied were as follows:

Trt #TreatmentSaltlbs ae
per gal
Rate
Quarts/A
Apps
1Glypho1Mono K4.54.671
2Glypho2IPA371
3Glypho3IPA371
4Glypho4Di-ammonium371
5Untreatednananana

Results

All products provided 100% control of annual bluegrass, bentgrass, and perennial ryegrass within 15 days after treatment (See percent control data for annual bluegrass and bentgrass in Tables 1 and 2). Some of the bentgrass recovered from crowns at 36 days after treatment (see Table 3).

The tall fescue was 99 percent dead at 24 days after treatment.

There were no statistical differences between the treatments.

Sensitivity to treatments by grass species from most to least was as follows: annual bluegrass, bentgrass, perennial ryegrass, and tall fescue. The bentgrass tended to be somewhat variable.

At 3 days after treatment, none of the bentgrass was injured and the injury to the annual bluegrass ranged from 17 to 25 percent.

At 5 days after treatment, 3 of the 4 treatments on annual bluegrass had 75 percent control and the bentgrass ranged from 25 to 47 percent control.

At 7 days after treatment, the bentgrass and annual bluegrass control were about equal.

The perennial ryegrass and tall fescue were not distributed evenly throughout the plots making it impossible to get good data for these species.

The two broadleaf weeds present, yarrow and white clover, were killed 24 and 36 days after treatment respectively but were only present in two plots. The yarrow was in a plot treated with Glypho1 (K Salt) and the white clover was in a plot treated with Glypho3 (di-ammonium salt).

Table 1: Percent Annual Bluegrass Control

   Percent Poa Annual Control
Trt #TreatmentRate
Quarts/A
3 DAT5 DAT7 DAT15 DAT
1Glypho14.6725%75%88%100%
2Glypho2717%75%89%100%
3Glypho3722%75%91%100%
4Glypho4718%60%91%100%
5Untreatedna0%0%0%0%
  LSD @ .051020.623.9Na

Note: Ratings for 24 and 36 DAT also had 100% control on all treatments.

Table 2: Percent Bentgrass Control

   Percent Bentgrass Control
Trt #TreatmentRate
Quarts/A
3 DAT5 DAT7 DAT15 DAT
1Glypho14.670%25%93%100%
2Glypho270%38%98%100%
3Glypho370%47%96%100%
4Glypho470%42%99%100%
5Untreatedna0%0%0%0%
  LSD @ .05na28.85.6Na

Note: Ratings for 24 DAT also had 100% control on all treatments.

Table 3: Percent Bentgrass Recovery – 36 DAT

Trt #TreatmentRate Quarts/A36 DAT
1Glypho14.670.20%
2Glypho271.50%
3Glypho370.50%
4Glypho470.40%
5Untreatedna0.0%*
  LSD @ .050.99%

* Since untreated plots had no injury, by definition, they had no recovery.