Welcome Run of Fall-Like Temperatures
The cool breezes and low humidity of mid-August have been a welcome relief for golf course superintendents in the region. Over the last 7 days, mean high temperatures were 2 to 6 degrees below normal in Missouri, giving weary cool season turfgrasses a much needed break. June, July, and early August took their toll with above normal temperatures and in July with very high humidity (4th highest average dew point on record). As stated in some previous years, it wasn’t the high highs that got us, but the high lows. Over the last 90 days, low temperatures have been 3-4 degrees above normal, meaning sustained high soil temperatures (~90 F in some areas) and no rest for weary cool season grasses at night. Tall fescue/Kentucky bluegrass lawns that were mowed too low or overirrigated (little supplement necessary in July) were particularly hard hit with disease, as were bentgrass putting greens with both disease and pure physiological decline. Hopefully this fall recovery-type weather is here to stay.
An intense tropical system brought considerable rain to the Bootheel (over 12 inches in some areas) and St. Louis last week, while Kansas City and the western portion of the state have been on the dry side this month. Slightly above average chances of rainfall are predicted over the next 6-10 days, with an above average chance of higher than normal temperatures. The good news is the average temperature for this time of year is starting to plummet towards the mid 80s, and the daylength or overall time period of intense height is smaller. Thirteen hours of sunlight delivers a much lighter punch than the near 15 hour days in June and July.
Late August Outlook
Scout for Fall Armyworms
2015 NTEP Bentgrass Rating
Number in parenthesis indicates percentage of total sites nationally that had the entry in the top quarter of all cultivars.
Sting Nematodes Found Again in Kansas City Area
“Awful tired now boss. Dog-tired.” This phrase in the movie “The Green Mile”, as painfully uttered by the hero John Coffey (played by actor Michael Clarke Duncan), sums up perfectly the current health of a creeping bentgrass putting green. As stated in the previous update, physiological decline, or the soggy hot root syndrome, has been commonplace in the region after the brutally hot and wet conditions of this summer. The June heat was the set, and the sustained heat and persistent rainfall of July was the spike on bentgrass roots.
Several of the submitted bentgrass samples to our diagnostic lab are also forwarded on to the MU nematology lab for a check on nematode populations that could stunt root growth. We observed root knot nematodes that again were at levels on some courses in St. Louis and Columbia that could impact turfgrass health. Lance nematodes were also noted earlier in the season at a course in southwest MO with above threshold levels. Ring nematodes were at or near threshold levels in a few other instances as well. Although bentgrass roots didn’t need any help in declining this summer, in very few cases have we seen devastating levels of these nematodes where they were deemed the primary or sole factor in bentgrass decline. At least until last week.
Sting nematodes were found at significant levels (24 – 192 stings per 100 cc soil) on several putting greens in the Kansas City area. Relatively speaking in a very microscopic world, sting nematodes are big nematodes with adults up to 3 mm long. The sting nematode also carries a big gun, in the form of a long stylet, or hollow fang, that pierces near root tips for feeding. The large stylet causes extensive tissue damage which provides a perfect infection court for other pathogens like Pythium spp. or the ETRI pathogens (ectotrophic root infecting fungi) that cause take-all or summer patch. Because of their size and destructiveness, stings carry the lowest population thresholds among the turfgrass pathogenic nematodes. On bermudagrass and zoysiagrass golf turf in Florida, the moderate risk threshold is 10 and the high risk threshold is 25 stings per 100 cc soil (Crow, 2015). Those thresholds would be set for warm-season turfgrasses grown in a tropical climate. In corn and soybeans, a common threshold is set from 1-10 per 100 cc soil. In this region, stings are impacting a cool-season species growing well out if its comfort zone in both mowing height and our oftentimes brutal transition zone summer.
The logical question is “where did they come from?” Since stings are such large nematodes, they should need a sandy soil with large pore spaces to move and thrive. Golf course putting greens with 85 percent + sand rootzone are a great habitat, but how did they get there? We have intermittently observed cases of damaging sting nematode populations in the Kansas City area since 2010, but have not detected them at all in St. Louis, Columbia, Springfield or other parts of Missouri. Because of this, it’s doubtful they are present in the topdressing or greens grade sand harvested from the Missouri River Bottoms that is commonly used in the region. In one earlier case, the introduction could have been zoysia sod harvested in sandy soils in lower Arkansas or Oklahoma and brought in, but that mode of introduction has not been consistent. Upon inspection of several soil surveys in the Kansas City area, the predominant underlying soil type seems to be a Kennebec series silt loam. The sand content of the upper horizon is stated at less than 10 percent, with a friable moderate fine granular structure. Although this doesn’t seem to be a suitable habitat for sting nematodes, more research is necessary to determine that they can’t survive in this soil type.
Luckily, there will be new tools available for superintendents dealing with sting nematodes in Kansas City. Indemnify by Bayer has received a federal registration, and will hopefully be broadly available in the area. Similarly, other companies are working on products that can hopefully tame the extra spike, or stylet of the sting nematode.
* To my knowledge, lawns and other higher cut turfgrasses do not have issues with sustaining considerable plant parasitic nematode populations, and sting has not been found associated with decline of higher cut turfgrasses in this region.
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Extension Turfgrass Pathologist
University of Missouri