Summer is back with a fury in late July, as temperatures are topping out at the highest of the season. This heat stress comes on the heels of spans of significant rainfall for each sector of Missouri. In separate, short 14 day spans from May – July, Kansas City, St. Louis, Springfield/Branson, and Columbia received 8-12” of precipitation (see animation below). With a few days left in the month, Missouri currently sits 2nd all-time in accumulated precipitation for May through July, with a real chance of eclipsing the record if a few more squalls occur. Remember May – June was the 5th wettest on record.
These preceding saturation periods resulted in reduced available oxygen which inevitably = reduced rooting, particularly on bentgrass putting greens. Also, excess water may still be trapped in soil profiles with high organic matter/thatch. This water is now hot, and may actually be boiling turfgrass roots and crowns. Getting the water out is imperative, and in many instances punching holes may do much more good than gratuitously driving a sprayer. This tough time for cool-season turfgrass, and methods to nurture it through this period, was detailed in the previous update.
The extended 8-14 day forecast provides some good news with a cool down on the horizon. Even through the end of this week, high temperatures are expected to dive out of the gaudy high 90s and lower to the more comfortable high 80s. Rainfall events are expected to remain frequent, however, meaning keeping soils dry and pore spaces oxygen filled will be difficult.
Brown patch affects perhaps the widest acreage of turfgrasses in Missouri. Home lawns, golf course roughs, and some sports fields are comprised of tall fescue. Brown patch is tall fescue’s Achilles heel and arguably the main reason for weed invasion. Numerous preventive fungicide applications are also necessary for brown patch control on golf putting greens, which are comprised of susceptible creeping bentgrass. The wet, humid summer of 2015 has produced consistently prime conditions for severe brown patch epidemics, even causing damage on non-traditional hosts like Kentucky bluegrass (and not just here).
Cultural practices such as restricting N fertilization in late spring/summer, minimizing shade, and reducing leaf wetness duration have been discussed in previous updates. If all these fail, brown patch management with fungicides seems to be an easy solution as many broad spectrum products are labeled for control. This year, however, accurate disease diagnosis and fungicide selection are critical.
Brown patch diagnosis, particularly on higher cut turfgrasses, is normally a cut and dry affair. Look for the tan lesions with the dark brown, scalloped margins and you’ve got it. This year, however, very little grass has been cut dry in the region. Conditions have been so ripe for this disease, that copious mycelium is also occurring on turfgrass foliage. Some of this mycelium production is not along patch margins like our typical smoke rings, but is occurring in small tufts throughout the canopy, more reminiscent of dollar spot or Pythium blight. Without a microscope or paying close attention to the symptoms, it’s been very easy to misdiagnose these outbreaks and chase the wrong disease.
As a report last year highlighted, research out of Oklahoma State University (Smith and Walker, 2013) provided evidence that consumer grade fungicides purchased by DIY homeowners at hardware stores/garden centers did not provide adequate brown patch control on shaded tall fescue. Twenty-one days prior to field day, we conducted a similar trial to evaluate curative brown patch control of two consumer grade granular products vs. three professional grade granular products applied once at label rates (shown in graph below). After 9 and 16 days after application, plots treated with the consumer grade product did not have statistically different brown patch severity than untreated control plots. The active ingredients in the two consumer grade products are in the DMI (propiconazole) and benzimidazole (thiophanate-methyl) class of fungicides. The QoIs or strobilurins have been consistently found to have greater efficacy on brown patch, and are the active ingredients (azoxystrobin & pyraclostrobin) in the three professional grade granular products that worked effectively in our study.
Follow on Twitter! @muturfpath
Like on Facebook! Mizzou Turfgrass
Extension Turfgrass Pathologist
University of Missouri