Creeping bentgrass's popularity as a fairway grass is rising due to improved varieties, as well as its resistance to gray leaf spot (to which ryegrass fairways regularly succumb). Converting to creeping bentgrass offers some challenges, however. A complete renovation to establish creeping bentgrass from scratch is effective, but forces course closure; a costly, unpopular step.

An alternative is overseeding for a more gradual conversion to bentgrass to avoid course closure. However, overseeding conversions have brought mixed success, depending on the species involved. Until recently, no studies had looked at overseeding success of creeping bentgrass in perennial ryegrass. Two Purdue researchers, Drs. Zac Reicher and Glenn Hardebeck, recently reported their research on this topic in HortScience.

Reicher and Hardebeck overseeded perennial ryegrass plots with Penneagle creeping bentgrass, using fall or fall + spring seeding dates and two different seeding rates (49 and 98 kilograms per hectare). They also looked at the effects of trinexapac ethyl plant growth regulator as a possible aid to overseeding success by suppressing the perennial ryegrass. Two different research sites were used — one with 100 percent perennial ryegrass turf, and another with a mixed stand consisting of about 70 percent annual bluegrass.

The researchers found no advantage to using the heavier seeding rate, apparently because this only increased seedling competition. They also found no increased overseeding success from using the PGR (though it did increase visual quality due to darker color). However, they made the applications to the ryegrass prior to seeding and suggest that post-germination applications may be a different matter.

They did find that at the site with pure perennial ryegrass, three years of overseeding (both fall and fall + spring) brought creeping bentgrass cover up to as much as 36 percent. This suggests that gradual conversion via overseeding could be successful, though it might take five or more years to accomplish.

By contrast, at the site that was primarily annual bluegrass, overseeding resulted in very little establishment of creeping bentgrass, apparently due to the more competitive nature of the annual bluegrass.

Given these results, Reicher and Hardebeck suggest that gradual overseeding conversion of perennial ryegrass to creeping bentgrass is feasible, if slow. However, substantial annual bluegrass populations will thwart conversion.

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