90s for Highs! Traffic Stress, Brown Patch, Crabgrass, and C4 Winterkill Recap
The final full week of June brought some of the hottest weather of 2025 so far to the Chicago area. As forecasted, high temperatures soared into the 90s for four consecutive days and were accompanied by warm overnight lows (70s mostly). Prolonged heat stress and elevated evapotranspiration led to visible golf cart traffic damage in roughs and the development of localized dry spots/hydrophobic zones on greens and fairways, especially earlier in the week. Creeping bentgrass exhibited marginal dieback, but Poa annua, with its inherently shallow root system, suffered acutely. Poa appeared faded, yellowish to lime green in color — signs of stress. Careful water management is critical to sustaining shallow-rooted Poa annua health through especially hot summer periods. Kentucky bluegrass, though more resilient, also began to bronze. In contrast, warm-season zoysiagrass is now thriving in Chicago District areas like central Illinois, with a characteristic vibrant green color indicating peak summer performance.
A shift in the weather toward the end of the week brought somewhat lower temperatures and much-needed rainfall. While the rain helped revive moisture-stressed turf, it also created favorable conditions for turfgrass diseases. As expected, brown patch was observed on a tall fescue tee at Bob Berry Sunshine Course. Additionally, a suspected outbreak of Pythium root rot was noted in the northwest Illinois region — a drainage tile malfunction of an otherwise properly built USGA-spec putting green was the issue. Timely fungicide applications and careful monitoring will be essential to prevent widespread disease development and protect turf health. Our forecasted highs next week will bring smiles for both golfers and our cool-season grasses as highs are to return to the 80s. Heat Dome, see you later!
Weather
Scouting for Disease — Brown Patch (Rhizoctonia solani)
Brown patch was observed in highly susceptible tall fescue. Brown patch is a common foliar fungal disease that affects cool-season turfgrasses such as tall fescue, creeping bentgrass, perennial ryegrass, annual bluegrass, and Kentucky bluegrass, especially during warm and humid weather.
Symptoms
- Brown circular patches (6 to several inches wide) in low mow turfgrass (< 1 inch) such as creeping bentgrass green and fairways.
- Brownish coalesced patches or infection in high-mown turfgrass (> 1 inch) such as tall fescue roughs or lawns.
- Tan colored lesions with a chocolate brown margin on leaf blades, which expands over time.
- Infection occurs when night temperatures are above 65°F and day temperatures are between 80°F to 90°F, along with high humidity (10 hours or more of leaf wetness).
- Thrives in environmental conditions that are warm, humid, poor air circulation
- Evening irrigation times (6 pm to midnight) exacerbate brown patch by extending leaf wetness durations.
Cultural Control
- Avoid excessive nitrogen fertilization (only spoon-feed nitrogen if possible) during warm, humid periods.
- Water early in the morning (after midnight) to minimize leaf wetness duration.
- Improve air circulation and drainage to reduce humidity (helps to burn off leaf wetness first thing in the morning).
- Mow at recommended heights (e.g., higher is better for tall fescue) and avoid mowing wet turf (reduces stress).
Chemical Control
Scouting for Weeds — Smooth Crabgrass (Digitaria ischaemum)
Smooth Crabgrass is a summer annual grassy weed commonly found in golf course fairways, greens, tees, and roughs, especially in thin and weak turf areas. Lawns are also prone to crabgrass especially when mowing heights are lower than recommended.
- Light green, narrow leaves with a smooth texture and a membranous ligule (fast growing and poor cutting quality due to high lignin content).
- Low-growing and spreads (aggressively) via tillers and seed production.
- Hairy leaves (pubescent), but less so than large crabgrass.
- Germination occurs in late spring to through summer (during June in 2025).
- Thrives in full sun, compacted soils, and areas with poor turf density (aerification is a plant health practice that helps to reduce weeds).
Pre-emergent crabgrass control is the way to go. Our most effective crabgrass preemergent herbicides have the active ingredients: prodimine, dithiopyr, or pendimethalin. All must be applied in early spring before crabgrass seed germination. Post-emergent crabgrass control is also effective using the active ingredients: quinclorac or fenoxcarp. Efficacy is best when crabgrass is still juvenile (1–2 tiller stage). In the late summer, established crabgrass is difficult to control.
Cultural practices for long-term suppression of smooth crabgrass
- Maintain dense and healthy turf via proper mowing and fertility.
- Avoid frequent and shallow irrigation that favors crabgrass germination.
- Annual aerification events will improve the rooting of compacted high-traffic turfgrass areas and thus increase turf density and reduce weeds.
GDD Tracker 4.0 — Turf Pest Management Tracking and Alerts (Michigan State Univ)
For more detailed information on smooth crabgrass, please refer to the smooth crabgrass factsheet by Dr. Aaron Patton, Purdue University.
Evaluating the suitability of cold-tolerant bermudagrass and zoysiagrass varieties for golf tee use in Chicago
A warm-season turfgrass study is being conducted at the Bob Berry Sunshine Course in Lemont, Illinois. It is testing improved varieties of bermudagrass and zoysiagrass (also known as C4 turfgrass) for use on golf courses in Chicago. This study is being conducted on a tee surface which represents a shallow sand-capped rootzone with native soil beneath. The existing colonial bentgrass tee surface was killed using a single application of glyphosate at its label rate on April 11, 2024. The killed turfgrass was retained to aid C4 turfgrass establishment. The mat layer helped to prevent weed seed germination and helped to 1) retain soil moisture, 2) maintain a consistent mowing height, and 3) allowed continued use as a playable tee surface.
Materials and Methods
The study is being conducted in a randomized complete block design with treatments consisting of 8 warm-season turfgrass varieties (4 bermudagrass and 4 zoysiagrass). Treatments are replicated five times and the individual plot size is 5 ft x 5 ft. Establishment used a 4 inch diameter plug of bermudagrass and zoysiagrass. In 2024, a total of two bermudagrass plugs of each bermuda variety were planted per plot on May 22. One week later, a total of four zoysiagrass plugs of each zoysia variety were planted per plot on May 29. After two weeks of establishment, regular mowing began at tee height with a Toro triplex reel mower (Cog Hill Golf & Country Club, Lemont, IL). Additional details are below.
- Monthly application of slow-release granular fertilizer, Forever Green Natural 4–3–0, at 0.5 lbs N per 1000 sq ft applied beginning 9 July to Oct, 2024, and Apr 4, 2025, to present.
- Herbicides were infrequently used to reduce competition by weeds. Application of Switchblade at 4 pints/acre to address broadleaves occurred on July 3, 2024, and June 24, 2025 (PBI Gordan, Kansas City, MO). Application of Revolver at 0.4 fl oz/1000 sq ft to selectively remove annual bluegrass occurred on July 25, 2024 and on June 17, 2025 (Envu, Carey, NC).
- Weekly, a hand edger tool is used to prevent entries from intermixing and thus maintain plot boundaries. Spray painted lines also help monitor and maintain contamination-free plots.
Objectives
- Evaluate establishment/lateral spread
- Evaluate persistence/cold tolerance
- Evaluate spring green up
- Evaluate dormant color retention
Data
For data collection, the best individual plug within each plot was selected for measurements. NDVI is used to supplement all visual ratings of color (TCM 500 Color Meter, Spectrum Technologies, Inc.).
- Lateral spread — Maximum stolon length from plug center (in.)
- Turfgrass Persistence — Visual cover (% per plot)
- Fall Color Retention — Color rating (1–9, 9 = dark green)
- Spring Green Up — Color rating (1–9, 9 = dark green )
- Percent Green Color (% per plot)
Results — Spring Green-Up and Winter Kill
This study experienced substantial winter kill during winter 2024–25 which has also been reported throughout the United States in a large region west of the Rocky Mountains (turfgrass transition zone to the upper Midwest).
Earliest to come out of dormancy
- Zoysiagrass (Meyer, Innovation, and DALZ1808) on Apr 29, 2025.
Late to come out of dormancy
- DALZ1701 zoysiagrass on May 28, 2025.
Never came out of dormancy or Winter Killed
- Bermudagrass (Tahoma 31, OKC3920, OSU15x9, and OSU1629)
Percent Green Color
- The average percentage of green color across five replications for Zoysiagrass (Meyer = 42.5%, Innovation = 42%, DALZ1808 = 13%, and DALZ1701 = 4%) on June 24, 2025.
- The average percent green color across five replications for Bermudagrasses (Tahoma 31, OKC3920, OSU15x9, and OSU1629) was 0.
Lateral Spread
- The maximum spring green-up lateral spread was observed for Meyer and Innovation zoysiagrass.
CDGA Green Committee Education and Communication
Final Photo
This attractive shrub is often cultivated for ornamental use. In the UK the cultivar ‘Annabelle’ has gained the Royal Horticultural Society’s Award of Garden Merit. The cultivar ‘Grandiflora’ has inflorescences which resemble snowballs, similar to Viburnum opulus ‘Roseum’.
Smooth hydrangea root was used medicinally by the Cherokee, and later, by early settlers for treatment of kidney and bladder stones. It has additionally been marked as a pollinator plant, supporting and attracting bees and butterflies. For more see Wikipedia
