Wet in the West
May temperatures have fluctuated, but remained mild throughout the region. Most areas of the state are 3-5 degrees below normal for the month thus far. These cool temperatures have caused considerable confusion for warm season grasses, which haven’t sprung back into action quite fully this year. This temperature pattern looks to change next week (see below) as summer temperatures are expected to ring in the first few days of June. For warm-season grasses the heat will be welcome, particularly zoysia looking to grow through intense large patch pressure. For cool-season grasses, the heat could spell the first arrival of heat stress and subsequent summer disease pressure.
May rainfall in Missouri has been between the have-way-too-much and the have-nots. May is typically the wettest month for the state and those in the KC and South MO would agree with that historical observation. Local areas around Springfield, Joplin and Kansas City are 4-5 inches above normal precipitation over the last 30 days. Columbia and much of central Missouri is an inch or two below normal for the month, along with St. Louis, which was dry for the first part of May, but has caught up considerably in the last few days. Significant rainfall is forecasted across the state in the next 5 days, with most again centered around the Kansas City area. This weather pattern is the perfect setup for our first bout of summer disease activity on cool-season grasses.
Next Week Outlook
Red Thread Popping
Red thread has been prevalent this spring on under fertilized cool season lawns & roughs.
Brown Patch Lurking
No widespread symptoms yet, but leaf lesions can be found in our indicator area at the turf farm.
MU Softball Regionals
Pythium Root Rot Conditions Prevalent
Last week saw the unfortunate arrival of a consistent enemy to bentgrass putting greens in Missouri. Pythium root rot was diagnosed at two golf courses, one in Kansas City and the other in SW Missouri. Both areas have been walloped with persistent rainfall, providing the pool (aka saturated putting green soil) which is the only thing this disease seems to require for infection. Interestingly, in both of these cases, however significant root-knot (216 nemas/100 cc soil) and lance (~3,000 nemas/100 cc soil) nematode populations were detected in the samples. Several prior research experiments have observed an increase in disease severity from a disease complex involving the combined forces of nematode infection and fungal or oomycete disease. This makes complete sense, as the piercing of the root cortex by a nematode stylet presumably would be a prime infection court for a root disease. In the future, assessing nematode activity in the spring on greens consistently affected by Pythium root rot may be wise to detect and control this potentially predisposing factor.
Pythium spp. are not fungi, but instead are oomycetes and more closely related to diatoms and algae. They persist in resistant structures called oospores, and spread through motile, flagellate spores called zoospores. They cause a number of different, and distinct turfgrass diseases; most commonly on leaves = Pythium blight, while on roots = Pythium root dysfunction or Pythium root rot. Pythium blight is common on Kentucky bluegrass, perennial ryegrass, and to a lesser extent on tall fescue lawns and creeping bentgrass fairways and tees. On established bentgrass putting greens, Pythium blight is rarely seen. Conversely, Pythium root rot is the most often diagnosed disease problem on bentgrass putting greens in the MU Turfgrass Disease Clinic. Pythium root dysfunction, as caused by Pythium volutum, is a disease most often observed on younger (<5-7 years) bentgrass putting greens that are well drained. Roots are tan and lack root hairs, a symptom we have not observed here in Missouri. In this region, superintendents most often mistakenly characterize their Pythium root issue as root dysfunction when in fact they have Pythium root rot.
Last year, 35 courses had significant Pythium root rot as evidenced by severe necrosis, oospore presence and in some cases significant and observable zoospore activity (see this video). Last week, I sent out a short survey to the superintendents who had a Pythium root rot diagnosis from the lab and inquired about watering and spring management practices. Twenty-seven superintendents responded (thank you!), and upon first glance at the data there aren’t many common practices among the respondents. One thing does stand out though - the amount of potentially root limiting products that are applied on greens in the spring. Preemergent herbicides, DMI fungicides (ahem), and plant growth regulators are all applied in the crucial spring root growth period prior to the summer marathon. While studies looking at these products alone show no appreciable decline in turfgrass quality or root density, perhaps adding a little water to all of them turns the cute Mogwai into a gremlin. Research is needed, but the subject is considerable food for thought… except after midnight.
Plans are underway for the 2016 Mizzou Turfgrass & Ornamental Field Day. The event will be held July 19th at our research facility at South Farms. Below are a few presentation topics to wet your whistle. Registration for vendors and attendees will be available shortly.
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Extension Turfgrass Pathologist
University of Missouri