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Questions from 2011 Educational Conference from Dr Ron Calhoun

Aerification and Annual Bluegrass

“When should I aerify to limit the establishment of new annual bluegrass plants?”

“You say that Poa germinates in the spring and the fall in Michigan. So when do I punch holes?”

These questions, and other like them, get asked a lot. Folks are concerned about punching holes when annual bluegrass is lurking beneath the surface, literally waiting for its moment in the sun. Research at MSU suggests that most annual bluegrass germination occurs when soil temperatures are between 55 and 75 degrees at the 0-2” depth. This temperature range occurs at the beginning and end of the summer meaning that annual bluegrass germination optima occur twice per year (lucky us). So, for irrigated sites in temperate climates like Michigan, you can have a spike in germination in the spring and late summer. However, the increasing soil temperatures in the spring are a harbinger of increased bentgrass growth. Annual bluegrass seedlings trying to establish in the spring of the year are faced with increased pressure from heat, drought, disease, and competition from creeping bentgrass, whereas seedlings in the fall face ideal growing conditions, cool nights, and limited bentgrass competition. So, although it’s not a slam dunk, aerification in the spring, before soil temps reach 55 degrees is likely to be your best option for encouraging bentgrass growth and minimizing annual bluegrass encroachment from germination and establishment of new seedlings.

Overheard from a weed scientist. "The will of the Poa to invade outlasts the will of the superintendent to keep it out."

Ronald Calhoun, PhD
Environmental Turfgrass Specialist
Michigan State University Extension
268 Plant and Soil Sciences Bldg.
East Lansing, MI 48824
ph. 517-355-0271 x 1139
fx. 517-353-5174

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