The St. Charles County Extension office will be hosting a lawn care workshop next Wednesday, September 25th from 6 - 9 pm. Justin Keay, Debi Kelly and I will be discussing all management aspects of lawns including soil testing, fertilization, cultural practices and pest management.
The goal of this workshop series (also slated for KC in early November) is to get homeowners and lawn care operators in the same room at the same time to get everyone on the same page.
Starting off by looking back a few weeks, August 2019 rounded out a meteorological summer with suppressed high temperatures but above normal low temperatures. This trend, which has been ongoing over the past two decades in Missouri, is driven primarily by higher summer dew point temperatures. Thus, the air has felt stickier and more humid in recent years, which in turn has led to longer periods of leaf wetness and more turfgrass disease.
To an astronomer, fall officially begins with the equinox on Monday, September 23 at 2:50 AM CST when the sun strikes the equator and the northern & southern hemisphere receive the same amount of light. The astronomers may have gotten it right this year, as September has felt more like summer than perhaps June - August 2019 did. Ninety + degree highs have been the norm, and only a late month cool down will presumably keep September 2019 from breaking the all-time record set in 1897. On a day with climate change politics and protests at the forefront, the data says that in the past 20 years Missouri has set six all-time monthly warm temperature records (Nov, Dec, Jan, Feb, Mar, and May) in the 130+ years of record keeping. Thank you to Pat Guinan, MO state climatologist for this information.
The forecasts indicate a temporary cool down after this weekend's cold front passes through, and then a high pressure ridge setting in to keep the jet stream at bay at the end of September and to begin October. This means a repeat of higher than normal temperatures to start our astronomical fall. Rain will impact much of the area this weekend, with 6" or more indicated in some localized areas of eastern Kansas and northwest Missouri. In the most rain battered area of the region by far, hopefully this short-term, and the long-term forecast indicated below, doesn't come to fruition.
The Rains Cometh
Summer Patch to the East
Black Layer to the West
Rust Sans Metal
Gray Leaf Spot Arrives with Force
For the last few weeks, bordering northern and eastern states have pronounced the arrival of gray leaf spot and unfortunately now we too can join in that chorus. At the turf research farm, gray leaf spot hit quickly late last week on our 'RTF' tall fescue plot leaving scattered saucer plate sized areas of blighted turf. Our neighbors have been experiencing issues on perennial ryegrass as well, which we fortunately do not utilize much here since it is extremely susceptible to this disease (and others). I surmise that many more gray leaf spot outbreaks on tall fescue are occurring in the region, however, and they are being misdiagnosed as brown patch.
Gray leaf spot symptoms will often appear more scattered in the sward compared to the more distinct patch-like symptoms of brown patch. The gray leaf spot pathogen (Pyricularia grisea) spreads via spores. These deposits via wind or water splash can create a different broad appearance across the landscape compared to brown patch, which spreads simply by more aggregated mycelium. Symptoms on individual leaf blades are characteristic and can also aid in diagnosis. On margins of affected areas, a distinct grayish spot with a dark brown/black border (as shown above and as the name implies) is observed on leaf blades. Brown patch lesions are normally tan with a dark brown margin and tend to run along the leaf blade, not resulting in a distinct spot. Blighted leaves with gray leaf spot may also bend downwards at the tip, resulting in a "sheperd's crook" type symptom.
Misdiagnosing gray leaf spot as brown patch can cause problems. Gray leaf spot is in many cases a more damaging disease that moves more quickly due to prolific spore production by the pathogen. Because the spores move up from the south and aren't presumed to be endemic due to our harsh winters, gray leaf spot occurs later in the season which can catch turfgrass managers off guard. In the last five years, gray leaf spot is therefore often observed in late August or September which is in the meat of aerification and seeding activities on tall fescue. Last but not least, fungicide control of gray leaf spot differs from brown patch. Throughout the summer season, azoxystrobin or other QoI fungicides are recommended for control. Azoxystrobin is not as effective on gray leaf spot, however, particularly populations that may have acquired resistance to it. A switch to thiophanate-methyl must be made if gray leaf spot is the culprit, and this fungicide is conversely not effective on brown patch.
If tall fescue is failing now, break out a 10X hand lens and inspect the leaf blades closely. If the symptoms aren't quite what you expect, and gray leaf spot is suspected, contact us and/or send it into the lab (www.plantclinic.missouri.edu) quickly for confirmation.
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Extension Turfgrass Pathologist
University of Missouri