It is possible to convert fungicide-needy perennial ryegrass fairways to Kentucky bluegrass without using nonselective herbicides. Researchers at Kansas State University tried a variety of techniques and combinations to determine the optimum conditions for Kentucky bluegrass (KB) to out compete perennial ryegrass (PR). They tried core aeration, scalping, plant growth regulators, high seeding rates, multiple seeding rates and post-seeding low mowing — all treatments were tried singly and in factorial combinations. As you may have tried, slowing PR by using PGR's did not help, nor did scalping and core aeration prior to seeding. What did work was a combination of post-seeding low mowing (PSLM) and high seeding rates. The post-seeding low-mowing treatment consisted of mowing at ¼-inch twice per week for a period of four weeks after seeding. At the end of four weeks, the KB seedlings were just reaching ¼-inch in height. With PSLM, KB population increased from 18 to 32 percent by 21 months after seeding. The researchers speculate that by keeping the PR very short, more sunlight reached the KB seedlings and allowed them to catch up to the PR. Typically, KB is seeded at 1.5 pounds per 1,000 feet squared. For this study, seeding rates were 2 pounds and 4 pounds per 1,000 feet squared, seeded in fall only or fall and spring. The multiple seeding didn't seem to offer an advantage, but the 4 pounds per 1,000 feet squared seeded in the fall increased the KB population from 20 percent to 30 percent by 21 months after seeding. It is still not as fast as killing out the fairway first, but should keep the area playable and gradually reduce the need for fungicides while the conversion takes place.

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