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The Heat is On!

You “Beverly Hills Cop” fans will recognize that title from the soundtrack of the 1984 hit movie that Eddie Murphy starred in. This song also seems appropriate for much of the mid-west and southern plains, as the number of turfgrass samples coming in to the OSU Turfgrass Diagnostic Laboratory has increased over the last several weeks. Obviously, the spring and summer growing seasons are typical periods when diseases of various turfgrass species are of most concern. Currently, most of the samples arriving in the laboratory are cool-season turfgrass species (fescue and creeping bentgrass). Many of the submitted samples are suffering from summer-heat related stress and are in general decline. Remember that cool-season grasses, especially fescue and creeping bentgrass grow best during the cooler seasons. When ambient air temperatures become hot (90 F+), growth of these grasses will dramatically slow or stop and can go into rapid decline. Root growth of cool-season grasses will cease when soil temperatures are above 80 F.

Currently, the average 2-inch under-sod soil temperatures for much of Oklahoma are in the low-to-mid 80s according to the Oklahoma Mesonet weather station network. In Stillwater, we are averaging around 90 F. Thus, root growth on cool-season grasses is not occurring. Research has also shown that as air and soil temperatures rise above 90 F roots will start to die. With high temperatures yesterday (June 10) in the triple digits and low temperatures not falling below 70 F (except for the pan handle) throughout Oklahoma, root mortality on cool-season grasses is going to be common in the coming days. For some areas the situation has been made worse due to prolonged drought and early onset of heat. According to the Oklahoma Climatological Survey, the month of June was the 2nd warmest and 4th driest on record since 1895. We have an average statewide precipitation deficit of 3.08 inches. 

Turfgrass plants that entered summer without a sufficient root system are more likely to not sustain growth, turn yellow or brown and go into general decline (see images). Symptoms of decline can resemble diseases caused by pathogens. Patch symptoms due to summer stress may look much like take-all patch. Turf can appear off color or golden brown and in areas where the plant stand is thin algae formation is common (see images). When roots are examined no evidence of the pathogens that cause these patch diseases are typically present. While evidence of root inhabiting fungi will often be noted, many of these fungi are simply naturally occurring root-inhabiting organisms that are not pathogenic. Also beware that while it may appear to the naked eye that the grass plant has deep or healthy roots this may not be the case. The vascular portion of the root is resistant to decay and may appear to be healthy when in fact it is dead.

To manage summer stress we are recommending good water and fertility management. Where appropriate, water very deeply and as infrequently as possible, while hand watering “hot spots”. ”Spoon feeding” may be necessary to sustain turf until temperatures are more favorable for cool-season grasses. Avoid damaging activities such as dethatching, aerifying, and any other management technique that can cause injury to turfgrass until it is again actively growing. A fungicide (such as Fore or Daconil) may need to be applied to keep algae formation under control on areas devoid of grass. Also, mowing heights should be raised. When the membership complains about slow greens, remind them that playing on slow greens might be better than playing on no greens.

Weather conditions in general have been too hot and dry for most turf pathogens. However, we did have one case of Pythium blight on a putting green where a severe case of scalping occurred and excessive irrigation was applied for multiple days. This resulted in an excessively wet environment that favored Pythium development. We also have observed brown patch on our research putting greens in Stillwater. Brown patch epidemics began this weekend and have increased over the last day or so.

Hopefully the heat will pass soon and we will have a nice cool August. Hey, stranger things have happened…

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