July 4th! Heat Stress, Early Root Decline, Etiolation?!?, Take-all Patch (more) and ABW Damage

We are now experiencing an especially hot summer — some have been saying we’ve been long overdue. For example, the last really hot Chicago summer dates back to 2012. During that Chicago summer, a hot July 4–6 stretch saw highs reach 100 degrees or more and reached 103 degrees on July 5 and July 6. More impressively, nights weren’t cooling either. It meant the average temperature during that three day period was 91.4 degrees — you had to go back to 1916 to find anything similar. Fast forward to summer 2025 and it’s feeling like 2012 again. When soil temperatures remain especially warm for an extended period of time, cool season turfgrass will suffer physiological decline. Roots shorten and lose root hairs. Years ago, creeping bentgrass research at Kansas State University taught us that supra-optimal soil temperatures (95 F) were more detrimental to roots than similar (95 F) air temperatures (Xu and Huang, 2000). And ever since, golf course superintendents monitor soil temps intensively about midsummer!

Image 1. All set for the fourth of July fireworks at Prestwick Country Club, Frankfort, IL. Settle, Jul 1, 2025

What’s in a dwarf? A true dwarf growing habit is most advantageous given a putting green height of cut (0.125 inches typical). Newer varieties with higher tiller density translates into higher photosynthetic rates (more leaves intercept more light) and thus should allow for greater heat tolerance. On golf greens, we’re about to find out. In the landscape lawns are also seeing some stress — the first significant drought of summer in unirrigated situations. For color, many things are now busting a move. For example, day lilies or Hemerocallis are in full bloom and one, ‘Stella D Oro’, is everywhere! A long, hot summer appears to be in the works. The good news is that all the preventative inputs to now are paying off. Whether in a pool or on a putting green, enjoy your 4th of July. Stay cool when you can!

Weather

Figure 1. An especially hot summer is in the works. We are now counting daytime highs >90F with regularity. More importantly, soil temperatures have remained the 80s which negatively impacts root growth. Physiological decline of cool season turfgrass is now occurring. Bob Berry Sunshine Course, Lemont, IL

Figure 2. Historical data of heat waves lasting 4 or more days in Chicago, Illinois. The last especially hot summer occurred in 2012.

Figure 3. Dry conditions are creating additional turfgrass stress especially so in unirrigated areas. Bob Berry Sunshine Course, Lemont, IL

Scouting for Abiotic Disorders — Heat Stress of Cool Season Turfgrass

Several reports of etiolation in creeping bentgrass over the past 14 days during a period of hot and dry conditions. This abnormal growth of creeping bentgrass is a rapid elongation and chlorosis (yellowing) of shoots. The most likely cause is supra-optimal temperatures and is based on historical experience. The last time the Chicago area saw etiolation of creeping bentgrass — on a multitude of golf courses — was during the record hot summer of 2012.

Figure 1. Etiolation of a creeping bentgrass fairway area at a Chicago-area golf course. Courtesy GCS, Jul 1, 2025

Figure 2. Etiolation of a creeping bentgrass fairway intermediate cut at a Chicago-area golf course. Courtesy GCS, Jul 1, 2025

Indirect Heat Stress

“Temperature may rise slowly above the optimal temperature range and persist for prolonged periods of time during summer. This may not be immediately fatal to plants, but it eventually causes injury or death. This is referred to as indirect heat stress. Indirect heat stress negatively affects turfgrass physiological and metabolic functions, including photosynthesis, respiration, transpiration, and water and nutrient uptake.” Fry and Huang

Symptoms — often confused with pathological problems

• Leaf chlorosis (yellowing)
• Shoot density reduction (thinning)
• Roots are less extensive versus in the spring (shorter)
• Root decline = dieback and reduction of new root formation

Transpirational Cooling — important heat avoidance mechanism

• Evaporative cooling is associated with transpiration
• Provides 5–18F cooler than air
• Stomata must be open for cooling to occur
• Requires a continuous water supply from roots to leaves
• Turfgrass varieties with long root extension is associated with heat-tolerant genotypes

Reference

Chapter 4, Temperature Stress. Applied Turfgrass Science and Physiology. 2004. Jack Fry and Bingru Huang. pp 83–110.

Scouting for Abiotic Disorders — Root Decline of Creeping Bentgrass

In a week, root decline has become apparent when processing diagnostic samples. This is common in especially hot summer conditions where cool-season turfgrasses are grown.

Summer Bentgrass Decline

“Summer bentgrass decline is a common occurrence on Agrostis spp. putting greens in tropical and subtropical climates. It may also occur in more-temperate regions during prolonged periods of hot, humid weather. Summer bentgrass decline is rarely observed where mowing heights are greater than 5 mm (0.197 inch), highlighting the importance of low mowing as a contributing factor.” Compendium Turfgrass Diseases, fourth edition

Symptoms

A rapid dieback of the root system is the most common symptom.

• Root hairs and fibrous roots are absent
• Epidermal and cortical tissues slough away from coarse secondary roots
• Lower, older leaves become chlorotic and then progresses to youngest
• Foliage turns yellow to orange, tan or brown and then collapses
• Appears in patches which correspond to bentgrass genotypes that lack vigor (heat tolerance)

Most Severe Symptoms

• Wherever air movement is restricted
• High-traffic areas
• Mower cleanup passes
• Poorly drained areas (turf often survives in recent aerification holes)

Image 1. Symptoms of summer bentgrass decline is often patchy because different biotypes react to stressful conditions differently. Some biotypes are more heat tolerant than others. Settle, Jun 30, 2025

Image 2. Recently sodded areas of greens and collars are often more vulnerable to summer bentgrass decline. Sod that is 1–2 years old can still be impacted because rooting remains compromised. Settle, Jun 30, 2025

Image 3. Roots with signs of summer bentgrass decline. Roots appear brown in color with cortical cells sloughing off. Also roots will have few root hairs or lack them entirely. Settle, Jun 30, 2025

Image 4. Healthy white roots with normal root hairs are now becoming difficult to find = a sign of summer bentgrass decline. Settle, Jun 30, 2025

Solutions — Six cultural practices are critical

1. Increase mowing height to at least 3.8 mm (0.15 inch)
2. Reduce mowing frequency to every-other day (utilize light weight rolling on alternate days)
3. Increase air movement (tree removal or fan installation)
4. Provide sufficient nitrogen
5. Manage organic matter accumulation
6. Use wetting agents/soil surfactants

Reference

Compendium of Turfgrass Diseases, Fourth Edition. 2023. Tredway, Tomaso-Peterson, Kerns, and Clarke, editors. pp 146–147

Scouting for Insects — Annual Bluegrass Weevil (Listronotus maculicollis)

Our first damage by annual bluegrass weevil (ABW) occurred within a week at two seperate golf courses in a fairway (Jun 27) and a putting green collar (Jun 30). It was associated with the first generation emergence of adults.

CDGA Research with Penn State

Shehbaz Singh and Kiara Talaber continue to monitor ABW development at two golf courses in the Chicago District. In summer 2023 ABW was first discovered at a few golf courses in Chicago. In summer 2024 ABW was confirmed at about a dozen golf courses in the Chicago area — all located in the north suburbs. We are providing samples for the McGraw lab at Penn State is identifying ABW and then enumerating to life stage. The research is sponsored by Syngenta.

Figure 1. Annual bluegrass weevils were first discovered at two golf courses in north Chicago suburbs in 2023. Courtesy Penn State Extension

Image 1. Damage to the Poa annua component of a creeping bentgrass fairway caused by annual bluegrass weevil larvae feeding on roots. Recorded ABW counts by McGraw lab: one 2nd instar, one 3rd instar, six 4th instars, and twelve 5th instars. Courtesy GCS photo, Jun 27, 2025

Image 2. The life cycle of the Annual bluegrass weevil. Courtesy photo, Ben McGraw, Penn State University

Image 3. The light brown color of this weevil indicates a new generation has emerged. As the ABW ages it will become almost black in color. This represents the 2nd generation of ABW. Kiara Talaber, Jul 1, 2025

The Bad News

• Both Poa annua and creeping bentgrass are vulnerable in golf course settings.
• ABW larvae feed on roots and this means a hot, dry summer will likely see more damage.

The Good News

• Newer classes of insecticides offer excellent control.
• ABW damage has only been identified at golf courses in Chicago’s north suburbs
• ABW does not impact homelawns

University Fact Sheets by Entomologists

Annual Bluegrass Weevil, Mar 3, 2025 update. Dr. Ben McGraw, Penn State.

Emergence of a new Illinois turf pest: The annual bluegrass weevil, Sep 11, 2024. Dr. John Schepis, University of Illinois.

Annual Bluegrass Weevil, Jan 29, 2024. Dr. Shaohui Wu and Henry Rice, Ohio State University.

Education & Communication by CDGA’s Green Committee

Let’s Talk About Trees

“Trees create a challange for our superintendents to deliver optimal turf conditions. Trees are dominant to grassand will always wint the battle for nutrients and water. Trees also block sunlight and air circulation whcih are essential to healthy turfgrass. You need to look no further than that patch of grass in your yard with the least sunlight to see the challenge firsthand.” Steven Green

Click here to read article

Final Photos

#Asclepias tuberosa or butterfly weed begins to flower in an out-of-play area at Bob Berry Sunshine Course, Lemont, IL. Settle, Jul 3, 2025

“Asclepias tuberosa, commonly known as butterfly weed, is a species of milkweed native to eastern and southwestern North America. It is commonly known as butterfly weed because of the butterflies that are attracted to the plant by its color and its copious production of nectar.” See Wikipedia for more

A single #ant can be seen feeding on a butterfly weed flower (Asclepias tuberosa). Settle, Jul 3, 2025

“A total of 70 ant species (Hymenoptera: Formicidae) from four subfamilies (Formicinae, Myrmicinae, Dolichoderinae, and Pseudomyrmecinae) were identified as pollinators of 41 plants from 23 families based on the data compiled from published records.” See Frontiers in Insect Science for more