In spite of the cool and dry weather, Poa annua continues to yellow and sometimes thin on golf greens. Last week Poa annua was thinning and dieing in low areas from too much water, heat, and humidity (photo). However, the cool dry weather over the weekend allowed for maximum water loss through evapotranspiration. Plus since many irrigation systems were still turned off after the monsoon-like rains over the last two weeks, Poa annua in the high areas is now turning yellow and thinning (photo). Regardless if the yellowing and thinning occurred from too much or too little water, the symptoms of the damage are virtually identical other than in the location on the green. Damage may be exaggerated by even low levels of summer patch or anthracnose (levels that may be undetectable by diagnostic labs). The high temperatures and high soil moisture the first two weeks of June likely compromised the Poa even further. Where to go from here? With the current cool weather, the damaged Poa is recovering quickly so we may have dodged a bullet in the short-term, but we’re sure to see more summer stress on the Poa in the future. Minimize stress on the Poa by insuring adequate control of both summer patch and anthracnose. Avoid topdressing, vertical mowing, or any stressful operation, but solid-tine aerification or spiking should be OK and will improve water and air movement into the soil. Insure adequate moisture since the root systems are compromised, which likely mean shallow and frequent irrigation. Spoon-feeding at 0.25 lbs N/1000sq ft or less should also insure growth without increasing stress. If you have areas that have thinned dramatically, consider shallow solid tine aerification followed by overseeding of a newer creeping bentgrass. Research shows the success of this is marginal, but recent data indicates the best chance of increasing bentgrass in a Poa annua stand is by overseeding in the middle of summer when Poa is weakest. The finicky nature of Poa annua over the last two weeks emphasizes how important it is to limit Poa annua infestation in the first place.
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