Cool Start to May, Continued Rain in the East.
Rain has dominated the weather story over the last three weeks, switching the pendulum quickly from the yin of a mild drought to the yang of a dramatic flooding event. Historic rains to close out April and begin May led to devastating floods and consistently saturated soils in many parts of the region. The statewide average precipitation total in Missouri was 9.86 inches, eclipsing the previous record in April 1994, and an astounding 5.89 inches above average. In the southern portion of MO and in northern AR, 10 – 20” of rainfall fell in April alone, causing numerous rivers and streams to overflow and inundating thousands of acres. As shown below, the major event occurred to end the month with 4 – 10” of rainfall occurring in the two-day period of April 29 and 30.
Historic Rain Event
Temperatures were approximately 4” degrees above normal in April, but have stayed fairly close to average to start May. This pattern looks to change in late May, with above average temperatures expected for the region in the 10 – 14 day NOAA outlook (see below). Unfortunately, the region doesn’t look to dry out either. May is typically our wettest month, with over 4.5” of rainfall expected. The Kansas City area has dried out, but St. Louis, Columbia, and Springfield have all received 2-3” of rainfall already this month. With this accumulated and forecasted rainfall, we may also expect a wetter than normal May to go along with our still soaked drawers from April.
Heat Expected to Return, Rain Expected to Keep Falling
Photogenic Warm Season Turfgrass Diseases
Large patch is continuing to severely damage zoysiagrass in the region, as wet and cool conditions are perfect for its continued development. Although earlier treatments would’ve been superior, curative treatments of flutolanil, DMIs like tebuconazole (only for golf) or QoIs like azoxystrobin can be used now to stop the disease from progressing further. Consider applying the fungicide in 2 gallons/1000 sq ft water carrier to get the fungicide a little bit further down onto the leaf sheath. As discussed in the previous update, a bit of nitrogen now may help rather than hurt zoysia recover from the disease.
Spring dead spot is now showing its teeth as bermudagrass continues to green up throughout the region. Unfortunately at this time of year, the damage is done and regrowth from the outside in is necessary. Begin fertilization as soon as possible on affected areas, and break up the matted areas with verticutting or raking. Later in June, consider fraze mowing or other aggressive aerification practices, and in the fall, apply 1-2 fungicide applications such as penthiopyrad on currently diseased areas.
Dollar Spot on Kentucky Bluegrass lawns is being observed in several areas now, particularly in Kansas City. This disease on Kentucky bluegrass is characterized by a bleached white lesion that spans across the leaf blade (as shown in the first picture here). Dollar spot can easily be confused with Ascochyta blight on lawns, so check with a hand lens for dark black specks within leaf lesions that are indicative of Ascochyta. Ascochyta blight normally requires no treatment and the turf will recover. Dollar spot, however, will need a little help, and treating with a bit of nitrogen (Careful! See below) and limiting leaf wetness will be necessary. In extreme cases, dollar spot may also require a fungicide treatment, with fluxapyroxad (Xzemplar) being a good choice for quick knock down.
Nitrogen fertilization of cool-season home lawns should be stopped or curtailed at this time of year. Major flushes of leaf growth on higher cut tall fescue or Kentucky bluegrass are not beneficial now, and may predispose the plants to more severe infections of diseases such as brown patch and Pythium blight. The current rains have made mowing nearly impossible to keep up with anyway, so a spike with urea or another fast release nitrogen source will only compound that problem. If nitrogen deficiency is observed (chlorosis in oldest leaves first), a slow release or organic fertilizer at modest rates should be used to correct.
Adult Billbugs Roaming
This hunting billbug found roaming on a putting green earlier this week.
Billbug adults are roaming now, and probably have been for quite a few weeks now. At a diagnostic visit, I noticed one strolling across a putting green in mid-Missouri, so their peak time is presumably now along with their egg laying. Zoysiagrass fairways and lawns have demonstrated billbug damage in early to mid-June, when larvae hatch, eat their way through stems, and continue to dine on roots in the upper inch of the soil profile. In areas with a history of damage, a combination of bifenthrin and imidacloprid sprayed at this time of year has been used with considerable success. If necessary, please apply these insecticides responsibly, with proper stewardship principles towards protection of bees, monarchs, and other pollinator species. These common-sense practices include mowing first, avoiding drift on windy days, avoiding application to flowering plants including weeds, using buffer strips around landscape beds, applying watered-in granulars instead of sprays, and applying in the early morning or late evening at times when pollinators aren’t actively foraging.
With the current extreme of wet weather, superintendents should mind to their most precious resource, roots on golf putting greens. By restricting root growth and depth due to anaerobic conditions, excess water in spring can also result in, or predispose, creeping bentgrass to more severe damage from soilborne problems. Along with take-all patch and summer patch, some disease problems are likely to be more prevalent this season as the infections occur now.
Pythium Root Infection Occurring
This bentgrass putting green root is exhibiting infection without aboveground symptoms.
While sampling an asymptomatic putting green this past week, I noticed some slightly discolored roots intertwined with normal, white healthy ones. Upon closer inspection in the microscope, discolored roots had a darkened vascular cylinder and with numerous Pythium oospores. Saturated soils cause Pythium spp. to quickly produce sporangia and motile zoospores, which swim in water films from one infection site on the root to another. Previous rains, and the likely continued wet weather in May will provide a prime breeding ground for the spread of this disease and pathogen infection. In areas with a history, watered-in preventive applications should have begun with a rotation of effective chemistries as mentioned in the previous update.
Most likely a result of the several new nematicide chemistries that have hit the market, several requests in the last few weeks have come in for nematode sampling. Now having the tools available to control the problem, means that knowing if the problem is there in the first place is a crucial piece of information.
The MU nematology lab has changed a bit, and is now entitled Soybean Cyst Nematode (SCN) diagnostics - http://scndiagnostics.com. While this name change reflects the major thrust of the lab’s services and expertise of the Director, it changes very little else about the lab’s operation concerning turfgrass samples other than a slight increase in price per sample ($50).
Proper sampling is a crucial, but difficult, aspect to getting reliable results to base management decisions upon. I prefer considering two scenarios for sampling, one based on a routine checkup or a chronic problem, and one based on an acute decline in which nematodes are suspect.
Routine or Chronic Problem (Damage not currently observed)
Acute problem (Current Damage)
The reason for the difference in methodologies is two-fold. If no symptoms are present, the first sampling method, (a shotgun approach akin to normal soil sampling), may pick up some aggregated nematode populations better with the combination of several samples. In the acute problem scenario, I want to know the population levels where the damage is most severe compared to an unaffected. Also, our lab grinds the sample including the thatch over our sieve, which is easier with the large diameter sample and in our experience raises the counts significantly.
Dr. Billy Crow also just released a timely article on the USGA Green Section that deserves attention. Click here to view the article.
Last but not least, these wet conditions provide the perfect opportunity to check the drainage on USGA or sand based greens, particularly at the sand/pea gravel interface. Concentrate on traditionally hard to manage areas, particularly low, “bowled” areas near the edges of greens. Using a long, one inch soil corer, drive down until you hit the pea gravel and pull back to inspect. Are you holding water at the interface or does the moisture level seem consistent? Are there color changes throughout the core that may indicate iron accumulation or black layer formation? Does the core have a sulfur smell indicative of black layer? How deep are your roots in this area compared to the middle of the green? The iron cementing subject was broached in this previous update from last August. Getting to know your root medium now during these times when water movement is necessary, may give clues to possible perils down summer’s road.
Plans are underway for the 2017 Mizzou Turfgrass & Landscape Field Day. The event will be held August 1 at our research facility at South Farms. Registration for vendors and attendees will be available shortly.
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Extension Turfgrass Pathologist
University of Missouri