May 29, 2023: Attention to Summer Disease Prevention – Turfgrass Science at Purdue University

May 29, 2023: Attention to Summer Disease Prevention

Highlights: Turfgrass disease prediction tool launches; drought stress on the horizon; disease season on cool season turfgrass starts with dollar spot and red thread/pink patch outbreaks; large patch on zoysia and bermudagrass and fertilization; prevention due for Pythium root rot, summer patch and other soilborne diseases; localized dry spot in dew patterns.

Turfgrass Disease Prediction Tool Launched

Dollar Spot Probability - Smith/Kerns Model 
The dollar spot probability based on the Smith/Kerns model can be utilized with this 
tool for the state.

Although a bit delayed this season due to technical issues, the turfgrass disease prediction tool has been launched and is available – In collaboration with the Purdue-housed Midwest Regional Climate Center, we’ve developed an Indiana site specific application to support management decisions for dollar spot with the Smith-Kerns model and soilborne diseases with two-inch soil temperature. Dollar spot probability can be visualized for the state, or your specific site can be zoomed into and selected on the map. Two-inch soil temperatures at 13 locations (mostly Purdue agricultural stations) throughout the state can be used to gauge timing of preventive spring applications for soilborne diseases such as fairy ring, summer patch and Pythium root rot.

Soil Temperatures to Guide Soilborne Disease Prevention
Two-inch soil temperatures at various locations in the state along with daily and 5 day averages can help guide watered in fungicide applications for soilborne diseases.


May temps normal for IN with below normal rainfall for much of the region.
Cool May start yielded to a quick warm up. — MRCC
Much of the region with below normal precipitation. — MRCC

May started off fairly cool with some areas flirting with early morning frost in low lying areas, although the temperatures did not get below 32℉ on the official weather stations. Temperatures warmed up quickly through mid-month leaving much of Indiana with close to normal temperatures, while out west in Illinois and Missouri temperatures were a few degrees above average. May rainfall followed the same below normal, carbon copy pattern as April with Indianapolis and much of the region. Average May precipitation is 4+ inches for the month, and much of the region is sitting at half of that with only stray pop up showers forecasted through the end of the month.  Drought symptoms are severe in much of central Missouri, and are now creeping into central IL and IN –

Temperatures forecasted to rise but increased rainfall not expected with it.
Warm, summer like temperatures arrive with June. — NOAA CPC
Rainfall chances not expected to climb with the temperature. — NOAA CPC

Heat into the 90s is expected this week into next for the first real feel of summer-like temperatures in Indiana since September of last year. Rainfall chances aren’t expected to increase with the temperature at least through the middle part of June, and drought dormancy would be expected on non-irrigated lawns and other turfgrass areas over the next few weeks. Fortunately, the seasonal outlook released on May 18 doesn’t forecast an expansion of drought beyond Missouri eastward for the entire summer –

Lawns: Drought dormancy

Drought Dormancy Taking Hold
Cool season turfgrasses going dormant with current drought conditions. Investigate soil conditions in areas to ensure they aren’t an underlying cause.

A lack of rainfall has incited drought dormancy on many areas of nonirrigated turfgrass including home and commercial lawns over the last week. Fortunately, Kentucky bluegrass and turf type tall fescue have very good drought dormancy mechanisms and can survive several weeks without supplemental water. The key is not to bother them until rainfall resumes and resparks growth. Just because it’s dormant and brown doesn’t mean the turfgrass is going down. Don’t apply any fertilizer, herbicides or other chemicals to the lawn when it is brown and dormant. Don’t mow while grass is dormant and stagnant; if the grass hasn’t growed then it shouldn’t be mowed. This, hopefully brief and slight, period of drought allows the opportunity to make note of irrigation pattern and efficiency, and perhaps problematic areas in a lawn that could be impacted by tree roots or poor underlying soil. For more information, transport back to the drought of 2012 with this special drought article by the Purdue turfgrass team –

*Lawns: On Brown Patch Watch*

 Quick note to be on the lookout for brown patch on tall fescue, particularly on irrigated lawns in this warm weather.

Golf: Localized Dry Spot Pattern in Dew Patterns on Golf Greens

LDS causing dew patterns on greens
Indication that putting green soil is dry and the sand is potentially hydrophobic.

In mid-May, our research greens at the Daniel Turfgrass Center showed distinct dew patterns indicating localized dry spot was developing. Dr. Bigelow has done years of surfactant work and as shown in the background has a good crop of hydrophobic sands on which to conduct this research. On our disease control trials, however, these dew patterns were a sign that treatment was necessary to remove this confounding effect from our experiments.

Red Thread/Pink Patch & Dollar Spot Update

Red Thread/Pink Patch on Fine Fescue; Dollar Spot on Bentgrass Greens
A. Red thread/pink patch apparent on fine fescue.
B. First dollar spot outbreak on research green at Daniel Turf Center.

Red thread and its collaborator pink patch was observed on a fine fescue lawn in mid-May, but outbreaks have not been as severe on tall fescue as was observed last year in research plots. A lack of humidity that accompanied the cool weather of last spring has presumably hampered development of this disease in lawns. Similarly, dollar spot has just started to fire on our bentgrass putting greens this year as opposed to the big explosion in mid-May in 2022 in our research plots. Dollar spot outbreaks, or lack of them, can be visualized along with the Smith Kerns model. Reports of dollar spot activity in southwestern IN came in mid-May which coincided with probability increases sparked by spring warmth and humidity. Up in mid and northern IN, outbreaks didn’t take hold until later due to low humidity.

Sports Turf: Large Patch on Bermudagrass & Zoysia

Large Patch on Bermudagrass & Zoysiagrass
A. Large patch on ‘Tahoma 31’ hybrid bermudagrass.
B. Large patch on ‘Meyer’ zoysia.

In mid May, large patch showed its teeth on both zoysiagrass and bermudagrass (hence the reason it’s not called ‘zoysia patch’) in untreated areas at the Daniel Turfgrass Research Center. The disease is becoming as common on hybrid bermudagrass sports fields as it is on zoysia golf fairways, with a major difference in the lack of severity on sports fields. On golf fairways, prevention in the fall and/or spring is often necessary, whereas on sports fields symptoms can often be treated curatively or simply fertilized out of. At this point, both warm season species should receive nitrogen soon regardless of disease occurrence, as previous research shows fertilization does not increase large patch severity.

Soilborne Disease Prevention –
Summer Patch & Pythium Root Rot

Prevention of soilborne diseases with watered-in fungicide applications is necessary on golf greens, sports fields, and high amenity turfgrasses, particularly if the area has had a history of disease occurrence. Soil temperatures throughout the state of Indiana have risen to above 65 degrees F, or the threshold for prevention of summer patch on Kentucky bluegrass, creeping bentgrass, and annual bluegrass. Two – three fungicide applications are recommended for control of this disease, with many fungicides in the QoI, DMI, or SDHI class available and effective. While these fungicide classes are broad spectrum and effective against other soilborne disease problems, they are not effective alone for prevention of Pythium root diseases such as dysfunction and root rot on golf putting greens. Segway (cyazofamid) and Serata (picarbutrazox) are the two most effective chemistries, and the time has also arrived to institute those in a preventive program on golf greens with previous issues. Remember for all of these soilborne diseases, that these fungicides must be watered in with at least 1/8” of post application irrigation (preferably 0.2 – 0.25”) to be effective.

Save the Date: 2023 Purdue Turfgrass & Landscape Field Day – July 18!!

Lawn Care Diagnostic Training – August 1, 2023


Lee Miller
Extension Turfgrass Pathologist – Purdue University 
Follow on Twitter:  @purdueturfpath


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