ALL: Have you observed gray leaf spot on tall fescue?

Yes - Needed to control
Yes - Didn't need to control

Update (9/20/2019)

A Spot of Gray

Printable Version [PDF]

STL Professional Lawn Care Workshop Next Wednesday

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.

Click here to register


Hot September

  1. September 2019 temps will tempt the record books. – Missouri Climate Center
  2. Heat expected to return in late Sept/early October. – NOAA

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

  1. From Friday - Sunday, extensive rain expected along cold front boundary. – NOAA
  2. Rain chances high for much of the central region to round out September. – NOAA

Quick Hits

    Summer Patch to the East

    1. Roots with black vascular tissue infected with the summer patch pathogen.
    2. Pathogen hyphae coming out of the vascular tissue is never a good thing.

  • Summer Patch Persistent on Putting Greens: In the St. Louis region, summer patch has been persistently observed on putting green samples submitted into the plant diagnostic lab. While in some instances this is an add-on problem to nematode feeding, summer patch has also been a critical factor in some cases of root decline. Curative recommendations for summer patch center on watered-in applications of Briskway, Lexicon, or other QoI fungicide + summer safe DMI/SDHI combination combined with a 0.1-0.2 lb N/1000 sq ft application of ammonium sulfate.

  • Black Layer to the West

    1. Despite aerification attempts, black layer can dominate the soil profile.
    2. Roots can be coated with black layer, and obviously cease to function.

  • Black Layer Where Rain Persists in the West: On the flip side of the state and spectrum, black layer has been pervasive on several green samples submitted from Kansas and the Kansas City area. This should be of no surprise considering the considerably higher precipitation amounts the region has endured over the last 3-4 months. Disappointingly to several superintendents, core aerification, Dryject, and Drill-n-Fill over the last two weeks hasn't solved the problem as shown in the above photo. While these practices are a necessary start, they don't impact a large proportion of the soil profile which should be considered in both width and depth down to the drainage tile. In areas with black layer, continue to check drainage by making sure water exits where it should during heavy rains/irrigation events and taking a deep core down to the pea gravel layer to check for iron cementing and/or black layer at the bottom of the greens profile. If black layer is still persistent, restrict fertilization with ammonium sulfate (unlike summer patch) and move towards a nitrate-based N source.

  • Rust Sans Metal

    1. Rust pustules produce thousands to millions of spores.
    2. Enough rust spores to turn black shoes orange.

  • Rust on cool-season grasses – At the research farm, tall fescue, Kentucky bluegrass and perennial ryegrass are stricken with rust, turning shoes and golf cart tires orange with spores. In established, dense turf areas, the disease is little more than a nuisance and normally doesn't result in appreciable damage. In newer seedlings, however, the disease can thin turf and allow for weed encroachment. Rust is favored by drought or nutrient deficiency, so the presence of the disease may indicate a need for irrigation and/or nitrogen application (notice the clover in the above photo?). In the rare case fungicide intervention is recommended in this region, QoI or DMI fungicides are most often utilized for control.

More Than a Touch of Gray

Gray Leaf Spot Arrives with Force

  1. Infected leaf blades will have small spots that progress quickly to a full blight.
  2. The pathogen sporulates quickly and intensely on leaf tissue.

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 ( quickly for confirmation.


Lee Miller
Follow on Twitter!  @muturfpath
Like on Facebook! Mizzou Turfgrass
Extension Turfgrass Pathologist
University of Missouri