This article comes to us from Rick Tegtmeier, CGCS, Des Moines Golf & Country Club.
At DMGCC, we are like many other golf courses in Iowa, we have poa annua and we try to control the ugly seed heads that emerge in the spring. Many different types of growth retardants are used and we are no different. We use a combination of Primo and Proxy to control our seed heads. When we spray it on our fairways we use the following rates of PGR: Primo at 5 oz per acre (.11 oz/1000) and Proxy at 220 oz per acre (5 oz/1000). This is commonly referred to as the 5 and 5 program.
One thing we all struggle with is to when we start spraying the turf. In the case of poa annua seed heads, control must be done well ahead of the emergence of the seed head from the sheath area of the plant. We have found that using a Growing Degree Calculator has been our best tool to get the timing correct on when we do our first spray. I use a simple Excel spreadsheet to enter my daily temperatures and it automatically figures the cumulative total of Growing Degree Days.
My good friend Steve Cook, CGCS, MG,Director of Agronomy at Oakland Hills Country Club wrote an explanation on Growing Degree Days for his membership and I have included a little bit of that here. One thing to note is to make sure you know what model (base) of GDD calculator you are using. We use the 32 degree base at DMGCC and some people use the 50 degree base. Just make sure your cumulative days match your model!
Here is Steve’s explanation of GDD and how it affects the plant:
The growth rates of many biological organisms are determined by temperature. As temperatures increase, activity increases. One of the ways we measure the biological activity of plants and insects is Growing Degree Days or GDD. Knowing the GDD allows us to monitor a specific number and apply plant protectants (like insecticides) at the appropriate time in an organism’s life cycle to maximize control. It has applications for plants like crabgrass or poa annua as well. What is GDD and how is it calculated? We assume that an organisms growth rate increases as the temperature rises above a predetermined base temperature. Each organism may be given a specific base temperature. Knowing these activity thresholds is important and we monitor them depending on our target pest and optimal treatments.
This year the timing is much earlier than we normally spray. We do 2 sprays in the spring to control those pesky seed heads. There are some studies out there that advise you when to make the second application as well. This too is based on cumulative GDD’s. Until more work is done though, we will continue our program of spraying 21 days after the 1st spray. We typically apply some ferrous sulfate with the 2nd spray to mask some of the PGR effects. If you would like a copy of our Excel Spreadsheet shoot me an email and I would be happy to share it with you.
Rick Tegtmeier, CGCS
Des Moines Golf & Country Club