These studies were conducted in the 2000 season at the Ames Golf and Country Club. The objective was to determine if Bensulide, a preemergence herbicide, can be used to prevent the reestablishment of Poa annua back into areas that had been treated with Prograss (ethofumasate).

STUDY 1

The study was conducted on the same area used for the 1999 Prograss trial (see pages 35 and 36 the 2000 Iowa Turfgrass Research Report). This replicated field trial was conducted on the 14^th fairway. The Kentucky bluegrass fairway was estimated to have a 60% Poa annua cover in the area where the trial was conducted at the initiation of treatments. The study was arranged as a randomized complete block with 3 replications. Prograss was applied at 0, 0.75, 1.5, and 3 oz/1000 ft² to plots measuring 5 ft x 5 ft on the following dates: May 14, June 7, June 29, August 1, September 16, and October 12. Data were collected on percentage Poa annua control on September 16 and October 12. Each application was combined in a tank mix with Sprint 330 at 3.5 oz product/1000 ft² and urea at 0.1 lb N/1000 ft². Prior to September 16, no reduction in Poa annua was observed at any of the application rates. No phytotoxicity was observed on the Kentucky bluegrass at any time during the season.

The cumulative rate of application on the plots by September 16 was 0, 3.75, 7.5, and 15 oz/1000 ft². The cumulative rate on October 12 was 0, 4.5, 9, and 18 oz/1000 ft², and the total application rate for the season was 0, 5.25, 10.5, and 21 oz/1000 ft². On September 16, Poa annua was reduced by 0, 0, 43, and 88% in response to cumulative rates of 0, 3.75, 7.5, and 15 oz/1000 ft², respectively. By October 12, Poa annua reduction was observed to be 0, 25, 52, 93% in response to cumulative rates of 0, 5.25, 10.5, and 21 oz/1000 ft² Prograss. A final treatment for the season was made on October 12 which resulted in cumulative rates of 0, 5.25, 10.5, and 21 oz/1000 ft² Prograss for the season. On April 17, 2000, Poa annua reduction was 39, 72, and 97% in response to the cumulative Prograss applications of 5.25, 10.5, and 21 oz/1000 ft², respectively.

These same 5 ft by 5 ft plots were divided in half on April 21, 2000 and Bensulide (Betasan) was applied at 9.2 oz product (12.5 lb ai/acre) to one-half of each plot. The Bensulide treatments were randomly assigned and the study was conducted as a split plot study with Prograss treatments from the previous season as main plots and Bensulide treatments as subplots.

Table 1. The effect of Bensulide on Poa annua populations with and without previous application of Prograss in the replicated field trial from 1999.

NS = means are not significantly different at the 0.05 level.

The Prograss applications from 1999 numerically reduced Poa annua through the season. Bensulide applications had no effect on the Poa annua population at any of the data collection dates.

STUDY 2

The second study was conducted on an adjacent area of the fairway. In the 1999 season, superintendent Don Portwine treated the north half of the 14^th fairway with Prograss on the following schedule: May 20-3 oz, June 17-1.5 oz, July 13-1.5 oz, August 16-1.5 oz, September 24-1.5 oz, and October 18-1.5 oz/1000 ft². The total application rate for the season was 10.5 oz/1000 ft². The fairway was estimated to have a 60% cover of Poa annua and 40% Kentucky bluegrass at the initiation of treatments. Each application was combined in a tank mix with Sprint 330, an iron source containing 10% Fe by weight, at 3 oz product/1000 ft², and urea at 0.1 lb N/1000 ft². The treated area had approximately 25 to 30% infestation of Poa annua in the spring of 2000.

The second Bensulide study involved the establishment of 5 ft x 5 ft plots on the area treated with Prograss the year before and two 5 ft x 5 ft plots on an adjacent area that had not been treated with Prograss. One plot on each area was an untreated control and the other received Bensulide at 9.2 oz/1000 ft². Treatments were randomly assigned and the study was conducted with 3 replications.

Table 2. The effect of Bensulide on Poa annua populations with and without previous application of Prograss.

NS = means are not significantly different at the 0.05 level.

Prograss applications in 1999 continued to reduce Poa annua populations through August of 2000, but the effect was no longer apparent in September. Bensulide did not reduce Poa annua populations at any of the rating dates.