Controlling annual bluegrass seedheads on golf courses

Kevin Frank<frankk@msu.edu>, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences -

Growing degree-days have accumulated very slowly this year, but within the next week many areas in lower Michigan will be in the optimum application window for applying plant growth regulators to control annual bluegrass seedheads on golf courses.

GDDTracker map for Proxy/Primo application timing.
GDDTracker map for Proxy/Primo application timing.

The slow start to the growing season has once again resulted in many questions regarding growing degree-days (GDD) and application timing for Proxy/Primo to control annual bluegrass seedheads. The green wave of GDD reaching the application timing will be moving into southern Michigan in the week week (see figure).

Many golf course superintendents use two applications of Proxy/Primo for managing annual bluegrass seedheads on putting greens. This combination has proven to be a reliable way to suppress seedheads and enhance turf quality in the spring.

GDDTracker starts measuring GDD on Feb. 15 and uses anything over 220 GDD (base temperature of 32 degrees Fahrenheit) as a guide to making the first application. However, Michigan State University Extension advises considering some factors. Both products are foliar absorbed and need living, green plant tissue for uptake. Applying Proxy/Primo to dormant turf will not be effective.

The decision of when to apply Proxy/Primo should consider the following factors:

  • GDD total greater than 220 (base 32 F).
  • Mowed at least twice.
  • Turf is 100 percent green.
Annual bluegrass seeding in a fairway
Annual bluegrass seeding in a fairway. Photo by Kevin Frank, MSU.

There is no benefit from applying your Proxy/Primo to dormant turf. However, if you have green-up, mowed and already made an application, cool temperatures should extend control. Air temperatures drive the metabolism of Proxy. Part of the reason the application range is so generous is that in cold weather it takes longer to get active in the plant, and in warmer weather it gets active faster. The activity of Proxy/Primo will either be “extended” by cold weather or “activated” by warm weather.

Typically, the second application is made 14-21 days after the initial application. 

Dr. Frank’s work is funded in part by MSU’s AgBioResearch.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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