Time for Primo/Proxy Applications

Forsythia bush in full bloom.  Picture taken March 19, 2012.

The winter season officially ended on Monday. With the mild weather we experienced this offseason, at times it seemed like winter never arrived. Central Iowa saw temperatures climb into the 80’s for five consecutive days last week. According to the National Weather Service, it’s the first time that’s ever happened during the month of March. Four inch soil temperatures are creeping into the low 60’s across most of the state. Forsythia bushes are in full bloom.

So what does this bizarre weather mean to you and your turf? The weather is well ahead of normal and agronomic practices will need to occur sooner than normal as a result. Avoid the temptation to schedule activities solely base on the calendar because this spring has been anything but normal.

Growing degree days (GDD) can help give you an idea of how unusual this spring is shaping up to be. GDD’s are a measure of heat accumulation and are used to predict plant and pest development rates. Daily maximum and minimum temperatures are used along with a base temperature to calculate a GDD value for each day. Below are two maps showing accumulated GDD’s from March 1 through March 20 for 2011 and 2012. As far as GDD’s go, most parts of the state have accumulated 2 to 3 times the number of GDD’s as this same time last year. In fact, it took until April 10 last season to accumulate the number of GDD’s we have experienced so far.

Growing degree day comparison from March 1 to March 20 for 2011 and 2012. 

Michigan State University has conducted research looking at GDD’s for a number of turf applications including Primo/Proxy applications. Their research indicates that the ideal GDD ranges for Primo/Proxy application is 200-500. Our accumulated GDD's indicate that the entire state is within the target range for Primo/Proxy. Now is the time to make your Primo/Proxy application for seedhead suppression of annual bluegrass.

Marcus Jones
Assistant Scientist
Iowa State University