Wednesday, April 8, 2015

Poa annua Greens Declining?

Dr. Kevin W. Frank
Michigan State University

In the last couple days I’ve received reports from several golf course superintendents indicating that Poa annua on putting greens that emerged from winter looking good was now declining.  It is possible that this is winterkill to the lower region of the crown that is responsible for root initiation.  For those of you that have Dr. Beard’s seminal textbook, Turfgrass: Science and Culture, on the shelf turn to page 235.  In the text Dr. Beard writes about differential low temperature tolerance between the upper portion of the Poa annua crown, responsible for new leaf initiation, and the lower portion of the crown, responsible for root initiation.  The upper portion of the crown has higher low temperature hardiness, i.e. can survive at lower temperatures. 

Green emerging from winter looking fine (March 16, 2015).

Poa annua on same green now showing stress (April 6, 2015).
Back in 2003, Dr. Beard taught the turfgrass physiology class at MSU and I was fortunate to attend many of his lectures.  I recall Dr. Beard describing a scenario in Detroit one spring when Poa annua emerged from winter looking just fine and in the matter of a couple days when the temperatures warmed everything died.  He indicated that this was the result of the lower crown suffering winterkill and although many thought the Poa was just dying over the weekend, it was in fact already dead.  Without the ability to grow roots the Poa annua didn’t survive long once the plant started ‘demanding’ water.  Take a look at the crown, if it's white and firm all is well, if it's brown and mush it's dead.  

I’m not certain that this is what happened this year or if it’s typical freezing injury that’s the result of cold night temperatures.  Freezing injury is typical this time of year and is especially evident on lawn height Kentucky bluegrass where the symptoms are tanning of the leaf blade down from the tip.  Warm temperatures and rainfall in the forecast should reveal whether or not what is being reported is indeed winterkill or hopefully, something less significant. 
Leaf tip freeze injury.