Cool May Set to Change
Temperatures in May have been below normal from approximately the Rocky Mountain range eastward. While Indiana through Ohio have been the epicenter of the cool weather, Missouri and much of Illinois have experienced four+ degrees below normal since the start of the month. Soil temperatures have remained at mid-April levels in the 55 - 60°F range for much of the month (see weather info from High Plains Regional Climate Center here). The cool April-May 2021 does mirror that of last year with below average temperatures, which set up healthier bentgrass, fescue and KBG, and less disease at least through the first 4-6 weeks of the summer season. This "break" last year was especially welcome through the opening grips of the pandemic. Summer seems to be coming down the track, however, as forecasts indicate a significant spike into June-like temperatures starting this weekend and lasting through the rest of May into June.
Widespread Rainfall Hopefully Will Let Up
Rainfall events over the last week have been consistent and soaking. Much of the I-70 corridor received most of the action, with two - three inches over the last 7-day period common. This being said, everyone in the region got doused at one time or another, leaving some flooding concerns near the Kansas City area along the Missouri river basin. Fortunately, with the arrival of warm weather, we are also forecasted to dry down. This slate of weather has prompted some of the best cool-season grass growing conditions since my start here in 2010, making the drier weather welcome so we can get to harvesting, aka mowing, it.
Perhaps a Dose of Summer
Dollar Spot Conditions Blooming
Cool Season Turfgrass Diseases on the Horizon: As mentioned above, cool season turfgrasses, with origins from Britain and Europe, are thriving in sustained cool, wet conditions. As discussed below, warm season turfgrasses have not enjoyed this environment. With the impending replacement by summer warmth soon, growth of cool season turfgrasses will soon be compromised. Therefore, we are presumably right on the weather forecasted, and historical, precipice of disease outbreaks on cool season turfgrasses.
Conditions for active dollar spot as indicated by observations and the Smith-Kerns model have been occurring for the past few weeks and were discussed in the previous update. With nighttime lows in the mid 60s and ample moisture persisting over the next few days, brown patch on tall fescue should start to become active. On high amenity areas with a history of the disease, monitoring for this disease and potential prevention should be on the docket early next week.
Soilborne Diseases on Bentgrass/KBG: Pythium root rot, summer patch, take-all patch, oh my. These soilborne diseases, particularly on creeping bentgrass putting greens and summer patch on Kentucky bluegrass sports fields, will be favored greatly in the recent and forecasted weather pattern. As noted in the previous update, prepare, prevent and protect.
Warm Season Diseases Thriving
As good as this spring has been for the cool types, the warm season species are wading in the woes. A frigid February and a much cooler than normal April - May has led to persistent issues with spring greenup and disease activity, including large patch on zoysia and spring dead spot on bermudagrass. As in most cases, disease and weather work together as a limitation on growing conditions not just limits production of leaf tissue but also reduces plant defenses.
Large patch has been extremely severe over the last few weeks, firing brilliantly on our research plots, golf courses and lawns. Some turfgrass managers have reported fall fungicide applications simply aren't holding on in the hot spots during this extended run of perfect weather for this disease. Others that haven't made a preventive fall or spring application are observing intense outbreaks requiring a curative application. While these curative applications halt disease progress, the symptoms persist in zoysia, and recovery in severely infected areas can take weeks if not months. This disease also provides a perfect vehicle for common bermudagrass to transition in. Zoysia should be primed to receive nitrogen fertility, which should be included in a recovery program. We've reported the importance of a well-timed fungicide application for this disease prior to spring symptom occurrence, and as shown in the photos above this spring again highlights this point.
Bermudagrass managers on sports fields or in the southern portion of the state have also bemoaned the terrible weather effect on growth (see comments). Remember the below zero temperatures in February, followed by record cold on April 21-22, followed by sub 40 degree lows this month. Although not receiving reports from elsewhere in the state, spring dead spot in bermudagrass is painfully obvious on our research plots here in Columbia. If bermudagrass is greening up slowly but uniformly at your site, prevention of this disease is probably partially responsible, and hopefully the warm weather on the horizon and a dose of N allows a steady green to gain view.
Pandemic caused, but not permanent, we will be holding the MU field day virtually this year. However, we are thrilled to announce the U of Arkansas Turfgrass Program has graciously allowed us to work with them in delivering a combined virtual field day later this summer. This partnership is extremely exciting, as we anticipate a dynamic lineup of turfgrass research presentations in this joint venture. The virtual format will allow us to accrue photo and video footage of experimental plots over the course of the season, rather than a still snapshot of conditions in late summer. Thank you to our great neighbors to the south, Dr. Richardson and the Arkansas team, for the willingness to collaborate. Stay tuned for more information soon.