The 1999-2000 Poa annua control trial included two parts. The first part involved application of Prograss (ethofumesate) 1.5 EC to golf course fairways on three golf courses in central Iowa by the course superintendents. The second part involved a replicated field trial conducted on the 14th fairway at Ames Golf and Country Club north of Ames, IA.

The courses involved in the fairway treatment study included the following locations and superintendents:

At Ames Golf and Country Club, superintendent Don Portwine treated the north one-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. Parts of the treated area that had been infested with creeping bentgrass were killed with Roundup on August 27 and seeded with a combination of Newglade, Bluemoon, Award, Rugby II, and Rambo Kentucky bluegrass.

At no time during the season were any signs of phytotoxicity observed on the Kentucky bluegrass. Observations on Oct. 12 indicated no significant loss of Poa annua in the treated area and there was no apparent damage to the germinating Kentucky bluegrass seedlings. Parts of the seeded area are split into treated and non-treated areas and observations of seedling survival and Poa annua control were made in the spring on April 17, 2000.

The area seeded with Kentucky bluegrass in the fall showed no reduction of germination in areas treated with Prograss during the 1999 season. Poa annua reduction was hard to determine in treated areas. The section of the fairway that had been estimated to have a 60% Poa annua population in the spring of 1999, had an approximate 25 to 30% infestation in the spring of 2000. However, the areas that were killed with Roundup and seeded to Kentucky bluegrass had at least 60% Poa annua and in some areas more than 60%. The population in these fall-seeded sections of the fairway was the same in areas treated with Prograss in 1999 as it was in areas that had not received the Prograss.

At Terrace Hills Golf Course, superintendent Bill Barker treated the 11^th fairway with Prograss on the following schedule: May 10-3 oz, June 3-1.5 oz, July 13-1.5 oz, August 10-1.5 oz, August 31-1.5 oz, October 8-1.5 oz, and October 29-1.5 oz/1000 ft². The total application rate for the season was 12 oz/1000 ft². Each application was combined in a tank mix with Sprint 330 at 3 oz product/1000 ft², and urea at 0.1 lb N/1000 ft². The fairway was estimated to have a 35 to 40% Poa annua at the initiation of treatments with the rest of the fairway covered with a combination of Kentucky bluegrass and Perennial ryegrass.

No phytotoxicity was observed on the bluegrass/ryegrass turf during the season. Most of the Poa annua died during a high stress period in late July on both treated and untreated areas. At the end of the season, Poa annua was germinating back into various areas on the course, but it was not possible to make an accurate estimate of Poa annua reduction in treated areas.

In April of 2000, the Poa annua population on the treated fairway had been reduced to less than 5%.

Bill also treated the collar areas of several greens with 3 oz Prograss on Oct. 8 and again on Oct. 29, 1999. All Poa annua in the treated areas died during the winter and he plans to overseed the areas with perennial ryegrass in April 2000.

At Hyperion Field Club, superintendent John Ausen began treatments on the fairway with Prograss on the following schedule: April 28-1.5 oz, May 20-1.5 oz, June 11-1.5 oz, June 29-1.5 oz/1000 ft². Each application was combined in a tank mix with Sprint 330 at 3 oz product/1000 ft², and urea at 0.1 lb N/1000 ft². The fairway is Penneagle creeping bentgrass with approximately 60% Poa annua. He suspended treatments in July when severe loss of Creeping bentgrass began to occur in the clean-up round on the outer edge of the fairway during a high-temperature stress period. The treatments were not resumed.

The replicated field trial was conducted on the 14^th fairway at Ames Golf and Country Club, adjacent to the fairway area treatment conducted by Don Portwine. 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 rates of 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 at 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 observed to have been reduced by 0, 0, 43, and 88% in response to cumulative rates of 0, 3.75, 7.5, and 15 oz/1000 ft², respectively (Table 1). 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.

We plan to continue this study by applying Bensulide, a preemergence herbicide that will reduce germination of Poa annua back into the plots, in the spring of 2000 to one-half of each of the treated plots. A report on the results of that trial will appear in next year’s research report.