Poa annua Greens Take A Hit In The Heat

By Pat Gross, director, Southwest Region
August 28, 2012

Poa annua greens are susceptible to heat stress as temperatures rise above 90°F. This is the time when energy consumption (respiration) exceeds energy production (photosynthesis).

Poa annua greens throughout Southern California have taken a beating over the past three weeks due to sustained high heat and humidity throughout the region. Turf samples sent to disease diagnostic laboratories from various courses revealed very little disease activity and the main reason listed for the turf decline and discoloration was high temperature stress.

Poa annua greens are especially susceptible to stress as temperatures rise above 90°F. Root growth stops and existing roots decline making it difficult for the plant to absorb water and nutrients. At that point, the turf enters the “dead zone” where food consumption (respiration) exceeds food production (photosynthesis). An excellent explanation on this situation is provided in the article Burning the Candle at Both Ends.

Golf facilities that have been able to survive during this time have been successful at taking preventive measures to keep greens cool and avoiding mechanical stress by adjusting their mowing program. Key points to keep in mind during sustained high temperatures:

  • Begin monitoring greens in the morning and throughout the day for heat and moisture stress. It may be necessary to begin syringing as early as 9:00 a.m. and at hourly intervals throughout the day to keep the greens cool.
  • Too much water can be just as detrimental as not enough. Water conducts heat, and a saturated rootzone can cause soil temperatures to rise rapidly and further damage the roots.
  • Cooling the greens with a light mist of water (syringing) in combination with the use of a blower or fan is an effective way to temporarily reduce surface temperatures as noted in the article Buffalo-blow Your H2O.
  • Consider switching to solid front rollers on putting green mowers to minimize the potential for scalping and mower injury. The change in rollers slightly raises the effective cutting height and provides more leaf tissue to help the turf survive.

For courses that have already suffered damage, there is little that can be done to produce a miraculous turnaround in a few days. Favorable environmental conditions are needed for turf recovery and the grass will begin to show steadily improvement as nighttime temperatures are in the 60°F range.

The Southwest Region team of Brian Whitlark (bwhitlark@usga.org) and Pat Gross (pgross@usga.org) are available to help golf facilities in the region with practical advice on how to manage turf during this difficult period. Please do not hesitate to contact either of us.

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