The uncommonly dry weather we’ve had in the past month has been tough on turf, and symptoms of drought stress are evident on local golf courses and other green spaces. The wilting and yellowing caused by lack of moisture can resemble symptoms of disease. At the UMass Extension Plant Diagnostic Lab we have seen an increase in submissions from home lawns and golf courses, particularly from fairways. While stress-related diseases such as summer patch or anthracnose may also be present, drought stress is frequently the primary issue. Most of these samples have also had another thing in common - excessive thatch layers.
Thatch is a dense layer of dead and living stems, roots, and leaves that lies between the turf and the soil. It is normally broken down by soil microbes; however, management practices such as fertilization rates and the use of some pesticides can affect the health of this microbial community, slowing the rate of thatch breakdown. Thatch buildup is therefore more common on intensively managed turf. Factors such as soil pH, aeration, species of turf present, and soil moisture level also influence the rate of thatch accumulation and breakdown.
Excessive thatch is detrimental to turf health for a number of reasons. It hinders deep rooting, dries out quickly, and restricts the movement of water into the soil. These qualities can seriously impair the ability of turf to withstand periods of drought. Thatch impedes the movement of fertilizers and some pesticides into the root zone, rendering these materials less effective. Thatch can also harbor pathogenic fungi that may cause disease on drought-stressed turf.
Under most circumstances, the thatch layer should be no more than 0.5” thick. When it becomes excessive, thatch management measures are imperative. Practices such as de-thatching or core cultivation are better done in cooler weather when desirable grasses are actively growing, so at this point in the season it is best to wait until late summer or early fall. In the meantime, there are other cultural methods you can use to improve the drought tolerance of your turf, such as raising mowing height, avoiding high nitrogen levels, and using judicious watering practices.
For more information on managing turf during drought stress periods, see the fact sheet “Management Tips to Improve Turfgrass Drought Survival” at https://ag.umass.edu/fact-sheets/management-tips-to-improve-turfgrass-drought-survival-0
Submitted by: Dr. Angela Madeiras