Friday, March 22, 2013

Seedhead Suppression

As we discussed last week, one of Poa's survival mechanisms is its ability to produce huge quantities of seed.  When this seeding takes place in the spring, it's one of the times that this turf can be frustrating for golfers.  The grass becomes bumpy, and it's not uncommon to see a ball heading toward the cup like a heat-seeking missile suddenly diverted by some Poa plant's chaff, just as a missile would be by...chaff.

What can be done to reduce the seeding and its bumpiness?  One of the best ways we can limit Poa seedhead production is by applying growth regulators.  Timing is critical with this application--there is a narrow window, and spraying a few days too early or too late will lead to limited control of Poa. 

How do we know when to spray?  When you compare March 2012 to March 2013, clearly there is a huge difference in spring temperatures from year to year, so this isn't an application whose date can be written on the calendar ahead of time.  As with many things on the course, we get down on our hands and knees and scout for signs of seedhead development.  However, in addition to this, one of our primary tools is a count of degree days.

Our application is based on a degree day model using 32 degrees Fahrenheit as a base.  Beginning on January 1, we take each day's average temperature and subtract 32.  For example, if the high temperature is 50 degrees and the low temperature is 24 degrees, we have a mean temperature of 37.  We subtract 32 from this, resulting in a degree day count of 5.  Our target for making the seedhead suppression spray is a year to date total of 450 degree days.

So, how good is the seedhead control?  The picture above (from 2012), clearly shows that there is a significant difference from the treated area to the untreated check plot.  However, even with optimal timing, this spray will never give 100% control. 

As mentioned last week, there are hundreds of different bio-types of Poa, and this genetic diversity will often lead to the plants seeding at different times throughout the spring.

The other challenge in timing the spray are the numerous micro-climates around the golf course.  That is, each green is going to vary slightly from every other green in terms of sunlight and temperature, meaning that a warmer green's Poa may be ready to go to seed a week or more before a cooler green's will.

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