July!?! Peak Heat Pauses, Spotted Spurge Broadleaf Weed, Purdue Field Day and Knotweed Research

The 2025 season brought an abrupt transition from May to July, skipping the crucial month of June that is vital for creeping bentgrass root development. The resulting heat stress led to poor rooting in early July, as evidenced by a drop in shear strength readings from 19.8 Nm to 16.9 Nm in our sand topdressing study. Turf plugs that typically held firm began pulling out during testing, clearly indicating weak roots. Fortunately, the second week of July brought a break from the extreme heat, with highs moderating to 80s and lows dipping into the lower 60s, conditions that should support recovery of creeping bentgrass and bring much-needed relief to Poa annua and Kentucky bluegrass, both of which were wilting under prior stress.

Image 1. Out-of-play areas with fine fescues have transitioned to a golden, straw-like appearance in July. The color change is a natural response to extended heat and dry conditions, as fine fescues enter summer dormancy to reduce stress and conserve moisture (growth slows, and green pigments are reduced). Seasonal dormancy is typical in low-input naturalized areas and nicely contributes to visual contrast on golf courses. Singh, Jul 10, 2025

In the northern suburbs, significant damage from annual bluegrass weevil (ABW) larvae was observed, with sampling revealing high larval pressure dominated by 5th instars, accompanied by younger instars and brown-colored adults. Peak emergence of the next ABW adult generation is expected within 1–2 weeks — keep scouting for signs of wilt/turf injury in putting green collars. Meanwhile, in the southern region, black turfgrass ataenius (BTA) grubs were detected in a creeping bentgrass fairway situation; these root-feeding larvae weaken turf, making damaged patches easy to lift, while increased bird activity serves as an additional indicator of infestation. On the disease front, dollar spot is now prevalent in untreated plots at the Bob Berry Sunshine Course. Additionally, fairy ring disease has been observed across fairways and roughs at both northern and southern golf courses. Hang tuff as a hot, humid summer season is upon us in 2025.

Weather

Figure 1. A break from heat stress occurred during the week of July 5–10. After a stretch of high temperatures in the 90s during early July, daily highs began to moderate, dropping from 92.2°F to 82.3°F. Likewise, nighttime lows fell from 71.8°F to 61.2°F. This cooling trend offers temporary relief to heat-stressed turf, especially cool-season grasses struggling under prolonged thermal pressure, Bob Berry Sunshine Course, Lemont, IL.

Figure 2. A much-needed stretch of consistent rainfall, totaling over 1.5 inches across four consecutive days. Notable rainfall events included 0.62 inches on July 10 and 0.35 inches on both July 8 and July 11. Good rainfall will help relieve drought stress and support turf recovery following an extended period of heat and limited precipitation in late June and early July, Bob Berry Sunshine Course, Lemont, IL.

Figure 3. Below-normal temperatures can be expected across the upper Midwest, which would offer continuous relief from recent heat stress. Long Range Forecast Courtesy. NOAA

Scouting for Weeds — Spotted Spurge (Chamaesyce maculata)

Spotted spurge is a fast-growing summer annual broadleaf weed commonly found in thin turf, bare soil patches, and disturbed areas on golf courses. It is sometimes used as an indicator weed for signs of what else may be lurking. For example, spurge is used as a sign of compacted soils in the Midwest. In contrast, in the southeastern United States and Florida, spurge can be a sign of root-feeding nematodes (sting nematodes in particular).

Characteristics of spurge

• Low-growing with a prostrate, mat-forming growth habit with reddish stems.
• Small, oval leaves often feature a reddish-purple spot in center.
• Milky Sap is visible upon stem breaking.
• Thrives well in hot, dry conditions and can germinate in compacted soils.
• Aggressively competes with turfgrass, mainly in stressed or weak areas.

Chemical control is most effective with pre-emergent herbicides such as isoxaben, dithiopyr, or oxadiazon applied in late spring before soil temperatures reach 60–65°F to prevent seed germination. Once spurge has emerged, post-emergent herbicides containing combinations of 2,4-D, MCPP, and dicamba can provide effective control.

Cultural practices for the long-term suppression of spurge

• Minimize open soil areas ad repair thin turf promptly.
• Promote dense turf through proper mowing, irrigation, and fertility.

Image 1. (Left) Spotted Spurge close up, and (Right) spotted spurge growing in winter-killed bermudagrass test plot. Bob Berry Sunshine Course. Lemont, IL. Singh, Jul 9, 2025.

For more detailed information on spotted spurge, please refer to the spotted spurge factsheet by Dr. Peter Landschoot, Pennsylvania State University.

Purdue Turf and Landscape Field Day

On July 8, we attended the Purdue Turf and Landscape Field day at the W.H. Daniel Turfgrass and Diagnostic Center. This annual event draws turf professionals from across the region to see turfgrass research happening at Purdue University. Distributers, industry reps, superintendents, and researchers gathered to exchange insights on turfgrass science, explore ongoing herbicide and disease trials, and discuss innovative solutions for managing lawns, golf courses, and sports fields. It is always a great opportunity to connect with peers and stay updated on the latest developments in the turf industry. More importantly, it was the first-ever turfgrass field day for Kiara Talaber (2025 CDGA Turfgrass Research Intern).

Image 1. Graduate student Mariah Cashbaugh presented her research on ‘Fungal DNA Detection in Perlocated Groundwater from a Golf Green Rhizosphere”. Her study explores the potential of using percolated drainage water as a non-destructive method to detect fungal pathogen DNA in turfgrass systems. By sampling drainage water from USGA-specified putting greens and analyzing microbial DNA using molecular techniques (e.g., qPCR), this approach could offer valuable insights into pathogen inoculum dynamics and soil health. Mariah’s work addresses a key challenge in turfgrass disease management (the accurate and timely detection of pathogen presence to guide fungicide selection and application timing). Singh, July 8, 2025

Image 2. Poster “Fungal DNA Detection in Perlocated Groundwater from a Golf Green Rhizosphere”. Mariah Cashbaugh, Purdue University. Singh, Jul 8, 2025

Image 3. Graduate student Vera Vukovic presented her research on 12 smooth crabgrass (Digitaria ischaemum) populations collected from across the U.S. Her study aimed to evaluate morphological variation, reproductive potential, and population-specific responses to climate and herbicide selection pressure. The findings will contribute to more informed and adaptive weed management strategies in turfgrass systems. Singh, July 8, 2025

Image 4. Side-by-side comparison of two smooth crabgrass species from Indiana, 1) quinclorac-susceptible (left) and 2) quinclorac-resistant (right). This visual represents baseline growth differences and highlights the ongoing research into resistance development and population variability. Singh, July 8, 2025

Image 5. Seeds of smooth crabgrass (Digitaria ischaemum). Singh, July 8, 2025

Post-Emergent Control of Prostrate Knotweed with Trimec Herbicide

A PBI-Gordon-funded herbicide trial to control Knotweed in Kentucky bluegrass roughs is being conducted at North Shore Country Club in Glenview, IL. Prostrate knotweed is a low-growing, summer annual broadleaf weed commonly found along compacted paths, cart tracks, and high-traffic areas on golf courses. Because knotweed has a single taproot it can tolerate soil compaction and out-compete turfgrass in those situations.

Image 1. A herbicide study to control prostrate knotweed in a Kentucky bluegrass rough. North Shore Country Club, Glenview, IL. Singh, Jun 30, 2025.

Materials and Methods

The study is being conducted in a Kentucky bluegrass rough near putting green 14 at North Shore Country Club. The study has four treatments in a randomized complete block design with four replications. A single application was made on June 9.

Objectives

• Evaluate post-emergent prostrate knotweed control with herbicides
• Evaluate turfgrass quality
• Monitor any phytotoxicity to turf

Table 1. Treatments for a PBI Gordon herbicide study to control prostate knotweed. North Shore Country Club, Glenview, IL

Measurements

• Prostrate knotweed control (%)
• Visual Quality (1–9 scale, with 6=minimum acceptable and 9=best)
• Normalized Difference Vegetation Index (NDVI) using GreenSeeker/Trimble HCS-100
• Phytotoxicity (%)

Prostrate Knotweed Control

The average initial knotweed infestation was 81.5% in the experimental plot area. A month after a single application on June 9, no herbicide treatment provided complete control of prostate knotweed. This shows how difficult broadleaf weed control can be with a single application.

• Trimec 992 (4 pints/A) — provided 60 % reduction from initial knotweed infestation.
• Experimental (4 pints/A) — provided 36.2 % reduction in knotweed infestation
• Trimec 992 (2 pints/A) — provided 28.75 % reduction in knotweed infestation

Figure 1. Percent prostate knotweed. A single application was made on June 9, 2025. North Shore Country Club, Glenview, IL.

Visual Turf Quality

• No treatment had an acceptable visual turf quality of 6 or more.
• Knotweed percent was more than 20% in all treatment plots.

Figure 2. Visual Turf Quality. A single application was made on June 9, 2025. North Shore Country Club, Glenview, IL.

NDVI and Visual Green Color

• Most herbicidal activity was observed for Trimec applied at 4 pint/acre
• NDVI and visual green color were lowest on 16 Jun and 23 Jun.

Figure 3. Normalized Difference Vegetation Index. A single application was made on June 9, 2025. North Shore Country Club, Glenview, IL.

Figure 4. Visual Green Color. A single application was made on June 9, 2025. North Shore Country Club, Glenview, IL.

Image 2. A herbicide study to control prostate knotweed in Kentucky bluegrass rough. North Shore Country Club, Glenview, IL. Singh, Jun 30, 2025

Education & Communication by CDGA’s Green Committee

“In the beginning, bunkers were supposed to be hazards, adding a significant degree of difficulty to a hole. Maintenance of hazards was haphazard at best because players were supposed to deal with whatever difficulties faced tem in what was largely an un maintained area. But that attitude has changed.”

Image 1. A 2022 CDGA Green Committee article on Bunker Liners and their importance in upkeeping the bunkers. Bunker Liners: Understanding a Trend in Course Maintenance. Click here for Magazine Articles for more.

Final Photo

Black-eyed Susan (Rudbeckia hirta) is in early to full bloom. This hardy native perennial thrives in full sun and well-drained soils, making it a favorite for pollinator gardens and low-maintenance plantings. Warrenville, IL. Singh. Jul 11, 2025

Rudbeckia hirta, often known as black-eyed Susan or yellow coneflower, is a flowering species native to North America and part of the Asteraceae family. This upright plant can reach heights of around 1 meter and produces bright, daisy-like yellow blooms with dark central discs. Rudbeckia hirta also holds the distinction of being Maryland’s official state flower. For more see Wikipedia