The Summer is FINALLY Over!

Clean-up and Slow Recovery Underway Following a Tough August for Turf Managers Peter H. Dernoeden, Ph. D.

Image 1) Excessive water from thunderstorms and hot days killed a lot of turf in August, 2016. Image 2) Large turf areas on this pocketed green likely were killed by mowing during a wet wilt event; Aug. 2016.

August 2016 was hot and shattered the record for the number of day temperatures exceeding 90ºF. High night temperatures (75ºF +) and high night humidity (70% +) stifled growth and promoted diseases. To add insult to injury, there were numerous heavy thunderstorm events. Excess water kills more grass on golf courses in summer than too little.  Excessive irrigation or heavy thunderstorm activity during summer can lead to problems such as scald and wet wilt. When water saturates thatch-mat (many roots are found in this layer in summer) and soil, oxygen is displaced from pore spaces and carbon dioxide increases. Roots need oxygen to survive and when pore spaces and thatch/mat are filled with water there is not enough oxygen to sustain the root system. Heat stress injury to the root system is accelerated in hot and wet soils.  Scald and wet wilt often occur simultaneously, producing similar symptoms and results. In many cases, damage was intensified by mowing during a scald or wet wilt event.

Image3) Sod is the only way to get greens back in play in a reasonable amount of time; Aug. 2016. Image 4) MSMA killed the bentgrass, but left bermudagrass unscathed in this approach; Aug. 2016.

Excessively hot and wet soils caused preemergence herbicides to breakdown rapidly by promoting their microbial decomposition, and large areas became inundated with crabgrass as well as goosegrass in compacted areas. Loss of turf density released Kyllinga to unmanageable levels. MSMA used to target goosegrass in bermudagrass killed cool-season grasses inadvertently contacted, while having little effect on the weed. On the upside, the drought from late August to mid-late September (regardless of irrigation) delayed annual bluegrass germination. Thus, early Poa competition was eliminated   for those who cored and/or verticut recently. As a consequence of severe turf loss, some greens and tees were re-grassed with sod.

Image 5) Tall fescue seeded into dead Kentucky bluegrass. Photo taken 21 days following renovation showing seedlings struggling with heat stress and rapid thatch drying in full sun areas; Aug. 2016.

I always have viewed late August as the “ugly time” for turf. Normally, the shorter days and generally cooler nights would help to speed turf recovery. Unfortunately, most of September was greeted with continued severe levels of heat stress, and was rain-free for about three weeks in most areas of the region. Overseedings performed in late August yielded weak, open turf and in some cases seedlings failed to survive. Tall fescue seedlings in renovated Kentucky bluegrass lawns and roughs struggled in large part due to dense thatch where the slicer-seeder could not get seed deep and below the thatch layer to make soil contact. Compounding the problem was lack of rain and thatch layers rapidly desiccated – even where irrigation was available.  Every turf manager appreciates that a soaking rain is superior to irrigation because of the uniformity of water deposition, and possibly a little nitrogen in the precipitation as well as better penetration of water and oxygen into soil. Had a few sufficient rain events occurred around Labor Day, most overseedings would have resulted in a much better catch. As a result of the heat and drought, many areas will require hand overseeding and special attention to hand irrigation in thin and/or bare areas to avoid overwatering greener areas. Turf managers must now be careful with their water management and scout daily for threats of damping-off diseases like brown patch and Pythium blight.

Image 6) Pythium damping-off in immature tall fescue. Image 7) Overseeded fairway awaiting rain to promote better germination; Aug. 2016.