Both by meteorological and astronomical standards, fall is in force today with the arrival of the fall equinox. It sure doesn't feel like it though, as temperatures have averaged 6-8 degrees above normal in in much of the region over the last 7 days, due to a stagnant jet stream over Canada. As obviously noticed, photoperiods will continue to get shorter until the winter solstice on December 22nd, when the approximately 9.5 hour daylength will start to expand once again. With the current heat wave, the shorter daylength (currently just under 11 hours) has a profound effect on reducing stress on cool season turfgrasses and putting warm season species such as bermudagrass and zoysiagrass down for their winter's nap. Some concerns have been raised over potential cool season seedling damage from the high heat and potential disease activity. At this point, we haven't noticed any problems, and last week's cool temperatures and rains should still be aiding quick establishment.
If seed and fertilizer were applied previous to it, last week's rains were ample enough to get seed off to a good start… that is if the seed didn't float away as may have been the case in Columbia. Precipitation totals are above normal, but variable across the state (0.6, 1.18, 2.62, and 4.75 inches above normal in Springfield, KC, STL, and Columbia respectively). At the MU turf research farm, we have been itching to seed a few new areas, including a perennial ryegrass NTEP trial and Kentucky bluegrass plot, but the weather just hasn't allowed us to get in the field. A 3-day rain event on Sept. 8-10 dropped 4.46 inches of rain, which was quickly followed by an additional 2 inches from events on Sept. 14 and Sept. 16. A soggy September is following the precedent set by July and August.
6-10 Day Forecast: Little more heat and rain expected to close the month
Rust Outbreaks Still Observed
Pest Management for Home Lawns Booklet
Large Patch Flares in Fall
As the pendulum swings to fall, large patch symptoms on zoysiagrass have flared up again. Last week's cool temperatures along with the heavy rainfall in Columbia (as noted above) has resulted in numerous large patch outbreaks at the MU research farm and two lawn samples sent into the Clinic. Symptoms can appear diffuse as small infection centers at this time of year, or as the more regular patch symptom. Although not as prominent as in the spring, the characteristic symptom this fall is an orange flagging of infected leaves on symptomatic plants. When the pathogen is really chugging, this flagging will result in a burnt orange, or firing symptom on the margins of infected areas.
In a month or so, depending on the weather, zoysiagrass will go dormant and symptoms will be indistinguishable. Now, however, is time to come up with a game plan of how to deal with both fall and spring symptoms. Scout zoysia areas and determine where outbreaks are occurring. Determine your fungicide strategy. If three fungicide applications are in your plans, the current suggestion is an application now (or even earlier) followed by another later this fall 21-28 d later in October, and another in early spring. Suggested 2 inch soil temperature threshold targets are a fall to near 70 F in September (lowest has been 74 F in Columbia hit last week) and a spring to 50-55 F in early to mid-April. Based on our research, a two application strategy should include a fall and spring application around these two thresholds.
If limited to a single application based on budget and/or client willingness, perhaps the best method is to simply scout out the affected areas now and identify the problem. Then follow up next spring in early – mid April (even while the zoysia is dormant) with an early preventive application. Spring large patch outbreaks, particularly during wet Mays, tend to cause the most devastating damage in this region of the upper transition zone. Preventing the disease from gaining a foothold early in the spring can get the zoysia through the prime infection period until the heat of summer kicks in and the zoysia can fend off the pathogen on its own. We've demonstrated fall applications (click here to read a previous report) are more erratic for spring control, and may require a rescue treatment. If only allowed a single use of the hammer, it would be wise to wait until spring to swing.
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Extension Turfgrass Pathologist
University of Missouri