Second Heat Wave! ABW Damage Now Occurring, Yellow Nutsedge, Dollar Spot and Moss Research
After a brief cool-down last week, we’re back into heat stress conditions with a return to the dog days of summer — highs in the 90s and lows in the 70s. Soil temps at a 2-inch depth are surging into 80s again and it is mirroring the stress we saw during the 4th of July weekend. Heat Wave # 2 is here. And the forecast? Similar heat is expected early next week, with upper 90s expected. Bentgrass rooting never fully developed this season which means shallow-rooted greens remain especially vulnerable to sudden midsummer heat spikes. When not at low mowing heights, both Poa annua and Kentucky bluegrass saw solid recovery over the past two weeks, but signs of physiological decline and dieback are likely to return. It is critical to stay proactive in 2025: Hand watering, monitoring moisture levels, and using needle-tine or solid-tine aeration can help relieve rootzone stress. Raising mowing heights is another solution! It may temporarily affect ball roll and firmness, but it’s a necessary adjustment to help turf tolerate the heat stress currently being experienced!
With the return of hot, humid conditions, dollar spot is seeing increased activity. Symptoms of this foliar disease are small dime-size, bleach-white spots on bentgrass greens, tees and fairways, whereas larger diameter spots occur in Kentucky bluegrass roughs (silver dollar size). This week at the Bob Berry Sunshine Course in Lemont, the creeping bentgrass fairway variety trial has disease (dollar spot infection centers) for the very first time. Brown patch has also flared up in areas with reduced inputs — an ‘RTF’ tall fescue (highly susceptible) tee and a ‘Piranha’ creeping bentgrass tee. Recent course visits have diagnosed new cases of annual bluegrass weevil (ABW) damage on the north side, particularly in collars where larvae are feeding on the crown and stem of Poa annua. Notably, much of the ABW damage occurred near areas where clippings were being discharged, reinforcing the critical role of clipping management in ABW control. Targeting late-instar larvae now will help prevent the emergence of first-generation adults and suppress further spread. The importance of scouting for pests is a good lesson each growing season, but especially so in 2025.
Weather
Scouting for Insects — Annual Bluegrass Weevil (Listronotus maculicollis)
In a week more golf courses (4) have reported ABW damage. All reports are from golf courses in a similar location — the north suburbs of Chicago.
Site 1: North Shore Country Club, Glenview, IL — Significant damage by annual bluegrass weevil (ABW) was observed in a Poa annua plus creeping bentgrass fairway. Soap flushing of the damaged area yielded approximately 68 adults per 9 sq ft (7.5 adults/sq ft). Larval sampling occurred and samples were mailed to Dr. Ben McGraw at Penn State University. His entomology lab detected the presence of teneral* adults and first instar larvae, but no other larvae were found. These observations suggest that the damage was likely caused by the emergence of first-generation adults.
*Teneral = An insect, immediately after molting when its exoskeleton is soft, pale, and not yet fully colored.
Site 2: Chicago Golf Course (north suburb)— Significant damage was observed in the collar region of the practice green, and two greens in play. Soap flushing in the affected areas revealed only 15 adults per 9 sq ft (1.6 adults/sq ft), which is well below the established damage threshold of 10 adults/sq ft. However, turf core sampling uncovered the presence of late-instar ABW larvae (stages 3–5), with 7 larvae and 2 teneral adults found in a single 2-inch turf plug. This suggests that the damage was primarily caused by late-stage ABW larvae feeding stem and crown of Poa annua. Timely detection and stage-specific scouting are critical for accurate diagnosis, as well as insecticide application.
Scouting for Weeds — Yellow Nutsedge (Cyperus esculentus)
Yellow nutsedge is a warm-season perennial weed commonly found in golf course roughs and out-of-play areas, particularly in poorly drained or over watered areas. More importantly, it is not a grassy or broadleaf weed, but a sedge weed.
- Bright yellow-green, glossy leaves with a prominent midvein.
- Triangular (V-shaped) stem cross-section, unlike round grass stems.
- Spreads via underground tubers and short rhizomes.
- Produces a distinctive golden-yellowish seedhead (umbrella-shaped with 3–8 spikelets).
- Emerges in late spring to early summer (soil temperatures 60–65°F)
- Prefers poorly drained areas that receive full sun.
Chemical control of yellow nutsedge
Yellow nutsedge is best controlled using selective herbicides containing the active ingredients halosulfuron, sulfentrazone, or mesotrione. Applications are most effective when the weed is young and actively growing, ideally between the 3 to 8 leaf stage. Treating at this stage is crucial, as it can prevent the plant from forming new underground tubers. Typically, two to three applications are required at 21- to 28-day intervals for effective control. To ensure maximum foliar absorption, avoid mowing for at least two days before and after herbicide application.
Cultural practices for the long-term suppression of yellow nutsedge
- Improve drainage in low or wet areas to eliminate the moist conditions that favor yellow nutsedge growth.
- Avoid overwatering and adjust irrigation to prevent saturated soils.
- Topdress low spots to improve surface grading and reduce standing water.
- Raise mowing heights to increase turf density and shade out young nutsedge shoots.
Factsheet
For more detailed information on yellow nutsedge, please refer to the yellow nutsedge factsheet by Dr. Aaron Patton, Purdue University.
Scouting for Disease — Dollar Spot (Clarireedia jacksonii)
Dollar spot is a common and economically significant foliar disease of nearly all cool season turfgrasses. Creeping bentgrass (certain varieties) and annual bluegrass are highly susceptible to damage by dollar spot. Kentucky bluegrass is also susceptible, but the disease is usually not treated with fungicides unless it is used as a tee or fairway surface.
- Small, bleached, straw-colored spots in low-mown turf like greens, tees, and fairways.
- In roughs, dollar spot can be mistaken for drought or nutrient stress.
- Leaf blades exhibit hourglass-shaped lesions with reddish-brown margins and bleached centers.
- Infection requires prolonged leaf wetness (10+ hours) when night temperatures are above 60°F and daytime highs range from 70–85°F.
- White, cottony mycelium may be visible in the early morning when dew is present — sometimes mistaken as Pythium blight.
- Conditions responsible for slow growth of turf, such as low nitrogen, exacerbate damage by dollar spot — slows recuperative potential.
Cultural Control
- Spoon-feed nitrogen to maintain adequate turf nutrition by consistently delivering low N rates during the summer months — alternatively use a slow-release nitrogen source.
- Reduce thatch accumulation — reduces moist microclimate conditions that favor dollar spot development.
- Improve air circulation and drainage — goal is to reduce humidity and associated leaf wetness (less than 10 hours leaf wetness desired).
Chemical Control
Silvery thread moss control in a creeping bentgrass putting green
We continue to evaluate alternatives to control silvery thread moss in a study funded by The Andersons. The trial is being conducted on a ‘Providence’ plus ‘SR1119’ creeping bentgrass nursery green at North Shore Country Club in Glenview, IL.
Materials and Methods
The study is being conducted using a randomized complete block design with 6 treatments and 4 replications. Individual plot size is 3 ft x 3ft. The first application was made on May 19, 2024 and applications are made every 14 days (8 total during entire growing season).
Three CDGA checks
- Check 1: 1/2 rate Quicksilver (carfentrazone, FMC Corp.). At a 1/2 rate, 8 applications can be utilized for moss suppression per year as per label.
- Check 2: Fiesta (8–0–1 with 14% chelated iron, Neudorff North America) applied at 3 lbs/1000 sq ft. This application rate corresponds to 0.24 lbs of nitrogen per 1000 sq ft every two weeks.
- Check 3: Urea (46–0–0) applied at 0.15 lb nitrogen per 1000 sq ft every two weeks. * In the previous two years of moss research, Fiesta effectively controlled moss. However, it remained unclear whether the control was due to the nitrogen component or the chelated iron component.
Objectives
- Evaluate moss control
- Evaluate turf quality visually
- Evaluate turf quality electronically
- Evaluate any phytotoxicity
- Evaluate indirect moss control — nitrogen stimulates creeping bentgrass growth and thus competes moss
Measurements
- Visual Quality (1–9 scale, with 6 = minimum acceptable and 9 = best)
- Normalized Difference Vegetation Index (NDVI) using GreenSeeker/Trimble HCS-100
- Visual Moss Infestation (%)
- Visual Phytotoxicity (%)
Preliminary Results
Moss Infestation
- Quicksilver — 70% reduction from initial moss infestation
- Experimental 1 — 59% reduction from initial moss infestation
- Experimental 2 — 72% reduction from initial moss infestation
- Fiesta 1/2 rate — 66% reduction from initial moss infestation
- Urea 0.15 lb N/1000 sq ft — 63% less moss from initial moss infestation probably by promoting the creeping bentgrass growth.
Visual Quality and NDVI
- Only Urea and Experimental 2 had acceptable visual turf quality (6.0 or greater) on at least one or more rating dates.
- Trends showed Urea and Exp. 2 had higher NDVI readings on many dates.
- Trends showed Quicksilver had lower NDVI readings on most dates.
Moss Health Rating
A moss health rating scale was created and used (1-Dead/Black, 2-Brown, 3-Yellowish Green, and 4 — Healthy Green).
- Quicksilver, Exp 1, and Fiesta reached brown to dead colored moss stage.
Education & Communication by CDGA’s Green Committee
Final Photo
Hibiscus syriacus is highly tolerant of air pollution, heat, humidity, poor soil and drought. The species has naturalized very well in many suburban areas and might even be termed slightly invasive, so frequently does it seed.
For more on Hibiscus, see Wikipedia.
