This post comes to us from Dr. Derek Settle from the Chicago District Golf Association
Late last week, I heard word that a green was thought to be showing symptoms of anthracnose basal stem rot. On Monday, in the rain, I made the visit. Indeed the green did have the typical signs. Poa annua was bright yellow whereas creeping bentgrass was fine. Areas of the green that would tend to show wilt stress were most affected. With a hand microscope that the Superintendent sues for field diagnosis, we both were able to see hair-like state and black discolored stems. The stems were easily detached when pulled because they had rotted.
The main cause was determined to be two-fold. 1) The weather. Coincidentally, I had noted that low relative humidity values were striking on Monday and Tuesday (this was already unlike season 2010 which always seemed blanketed in high humidity). The timing of the outbreak on Wednesday suggested the primary stressor was midday wilt. 2) Some DMI fungicides used for fairy ring prevention have little efficacy against anthracnose basal stem rot. Our course of action was to reduce plant stress on affected greens.
Reduce wilt stress: monitor greens closely for midday wilt.
Reduce fertility stress: increase nitrogen input as is feasible.
Reduce mowing stress: raise height of cut as is feasible.
Select best fungicide: use published fungicide trial information from plant pathology researchers across the United States.
For up-to-date fungicide recommendations I suggest the University of Kentucky 2011 Chemical Control of Turfgrass Disease guide