Cooler: Dollar Spot Eases, Scalp Injury, Leaf Spots, and Golf Tee Research

7 min readSep 23, 2022

Time moves fast. It is now the end of September. How did that happen? In a week we would experience temperatures that reminded us of midsummer (90+ for highs). But it wouldn’t last. The usual signs of fall are now in the landscape. For example, thornless honey locust (Gleditsia triacanthos var. inermis) are among the first to show fall color among our deciduous trees. A distinctive bright gold color has begun to light up its compound leaves. A second sign of fall, ouch, is increasingly dropping from oak trees. Acorn nuts are now building up in turfgrass areas beneath. Some, like me, notice because acorns are helpful when trying to identify oak (Quercus) species. Squirrels notice too and they are now busy “squirreling away” an important food source of winter.

Image 1. Flagged area represents a sand-based rootzone sprayed with a non-selective herbicide glyphosate. This is where a new creeping bentgrass variety trial will be conducted. Newer varieties are selected for resistance to dollar spot. This study will compare 20 varieties in plots measuring 4' by 8' replicated 4 times at Bob Berry Sunshine Course, Lemont, IL. Settle, Sep 22, 2022

On golf courses good turf establishment by seed continues. Few new issues exist other than the typical foliar diseases we know to expect — leaf spots and rusts. Until complete recovery, issues of summer will linger into fall. But it won’t last for long. We continue to watch rapid repair and renovation provided by superintendent, staff, and… Mother Nature. Without moderate air temperatures and adequate moisture via rainfall and automatic irrigation systems none of this would be possible. So enjoy this period of reestablishment/regrowth as you play the game of golf. Time moves fast.

Weather Update (Sep 3rd week) by Shehbaz Singh, MS

North Shore CC, Glenview. Temperatures during the week were mostly higher. As forecast, a sudden drop in air temperature occurred at week’s end. Maximum air temperatures ranged from 63 to 88°F over the last seven days. The highest of 88°F was recorded on Sep 21 (Wed) and lowest of 63°F was recorded the very next day (Thu). However, minimum temperatures continue to drop and we saw our first low below 50 degrees Lows ranged from 47.5 to 69.2 °F over the last seven days. Relative humidity was mostly lower than 80% except Sep 19 (Mon) and Sep 20 (Tue). Rainfall of 0.42 inches and 0.27 inches was experienced on Sep 18 and 19 respectively. Cumulative rainfall was 0.82 inches

Bob Berry Sunshine Course, Lemont. Air temperatures in the southern Chicago suburbs was warmer compared to northern Chicago suburbs. During the week, maximum air temperatures ranged from 65 to 94°F. The highest temperature of 94°F was recorded on Sep 20 (Tue) with a cool down by then end of the week. Minimum temperatures continue to cool and ranged from 43.5 to 67.8°F over the last seven days. Relative humidity continues to remain high and was higher than 80% on three of seven days last week. However, winds were present at about 4 to 6 mph on Sep 19–10 and Sept 22.

Figure 1. Air temperature and humidity conditions during September, 2022.

Scalp Injury Update

Introduction. In midsummer, scalp injury by mowers is a commonly seen in creeping bentgrass. It has a spreading, stoloniferous (or some might say thatchy) growth habit. Lower mowing heights are typically worst hit. That means golf greens are most vulnerable.

Scalp. We first noticed in August in a few of our research studies dedicated to dollar spot disease in a L-93 plus Providence creeping bentgrass nursery green at North Shore Country Club in Glenview, Illinois. Our best data this year came from a single fungicide study with 6 treatments and 4 replications.

Objective. The purpose of the study was to evaluate control of dollar spot by using a reduced rate of the fungicide Daconil Action (2 fl oz per 1000 sq ft) in combination with a green pigmented product called Activo (0.5 or 1 fl oz per 1000 sq ft) by Precision laboratories. Applications were every 14 days and occurred a total of seven times (Jun 6, Jun 20, Jul 5, Jul 18, Aug 1, Aug 15 and Aug 29). The final two dates of application occurred when scalp injury was present.

Surprise. Not so surprising was the finding that the addition of a plant growth regulator (PGR) called Primo helped to reduce incidence of scalp injury. And those treatments were associated with approximately 5% or less of scalping. However, we were surprised to find that all treatments with Activo were associated with reduced scalp injury. It suggests additional plant health benefits may be occurring with this product.

Products to reduce incidence of creeping bentgrass scalping (based on past and present CDGA research)

  • Plant Growth Regulators (PGRs) — Primo in this study
  • Activo — Behaved as a plant health promoting product in this study
  • N fertility (spoon-feeding urea) — Previous USGA research in collaboration with Dr. Dernoeden, Univ. Maryland (click here for more)
Image 1. Scalp injury in treatment plots of a Providence plus L93 creeping bentgrass nursery green at North Shore Country Club in Glenview, IL. Settle, Sep 22, 2022
Figure 1. In Aug-Sep, the four treatments which contained a pigmented product called Activo by Precision Laboratories consistently helped to reduce scalp injury versus untreated (red line). The addition of the plant growth regulator Primo tended to see the least amount of scalp injury; around 5% or less (see arrows).
Figure 2. Liquid nitrogen by urea* alone or in a tank mix reduced scalp injury of Providence creeping bentgrass. The effect was most prominent during the month of August. *Urea at 0.15 lb N per 1000 sq ft every 14 days

Leaf Spots of Creeping Bentgrass and Kentucky Bluegrass (Bipolaris and Drechslera)

Things like anthracnose impacting Poa annua in golf greens. Things like frog-eye scars in Kentucky bluegrass roughs caused by a root rot disease we call summer patch are now becoming a distant memory. A good reminder of why plant health combined with well-timed prevention is always an important aspect of the beginning as well as the end of each season.

Our newest issues are all about leaf spot fungi. Most have been brewing for quite some time, since sometime in summer, if you only ask some questions. But fall represents an ideal time for leaf spot diseases “to bloom” given heavy periods of dew are experienced. Leaf wetness abounds in the evening hours and then the dew/guttation doesn’t exactly burn off. Ten hours. A rule of thumb is a minimum of 10 hours of leaf wetness is required for most fungal diseases blight turfgrass.

Image 1. Hand mowing a golf green in the morning. Heavy periods of dew are now occurring. Settle, Sep 14, 2022
Image 2. Bipolaris causing reddish-brown spots in a Penn A4 creeping bentgrass green. Settle, Sep 14, 2022
Image 3. Incubation reveals conidia/spores of a leaf spot fungus called Bipolaris sorokiniana which infects Agrostis (or Penn A4 creeping bentgrass in this case). Settle Sep 18, 2022

Golf Tee Research by Shehbaz Singh, MS

Introduction. This week all tees at the Bob Berry Sunshine Course in Lemont were investigated. This is the second time this year we have conducted measurements of all tees. Previously, the 3-hole golf course was grassed with all creeping bentgrass tees. All previous tees were treated with the herbicide glyphosate to provide complete eradication and to then allow for newer surfaces. New establishment of various turfgrass species occurred in 2020.

Materials & Methods. Tees were evaluated using data of visual quality, Normalized Difference Vegetation Index (NDVI) using Handheld GreenSeeker device from Trimble Inc., visual estimation of percent contamination, and visual estimation of percent bare ground.

Objective. The objective was to evaluate the current quality of all tees following two years of establishment. It would then also allow us to begin repairs as early fall is a favorable time to do so for cool-season turfgass.

Visual Quality & NDVI Results

Best. Creeping bentgrass tees were better among all other turfgrass species. Most creeping bentgrass tees had visual quality ratings higher than 7.0 (Piranha, PC2 and Penncross). Also, NDVI ratings for the Piranha, PC2 and Penncross creeping bentgrass tees were higher, approximately 0.80.

Good. Kentucky bluegrass tees were also good having visual quality ratings of 6.6. Also, the NDVI ratings matched and were approximately 0.79.

Unacceptable. The tall fescue (RTF) tees had visual turf quality of 5.6 and NDVI ratings of 0.75. The perennial ryegrass (RPR) and colonial bentgrass (Musket) tees had visual quality ratings of 5.3 and 4.0 respectively. These tees were less dense which is probably due to their bunch-type growth habit.

Figure 1. Visual quality data for different turfgrass species and cultivars, Lemont, IL.
Figure 2. NDVI data for different turfgrass species and cultivars, Lemont, IL.

Contamination Observations

All tees were evaluated for contamination percent of other turfgrass species. It turned out to be a bigger problem than originally expected.

Kentucky bluegrass. The Kentucky bluegrass tees (HD Sport 2 and HGT) had contamination by creeping bentgrass of 63% and 70% respectively.

Tall fescue. One tall fescue (RTF) tee had 60% contamination by creeping bentgrass while another tall fescue (RTF) tee had 13.3% contamination.

Colonial bentgrass. Creeping bentgrass contamination of about 16.6% was also observed the colonial bentgrass tee.

Figure 3. Contamination data for different turfgrass species and cultivars, Lemont, IL.

Creeping bentgrass has an aggressive, spreading growth habit which enables this species to take over other less aggressive or bunch-type grasses. Nevertheless, contamination was also observed in creeping bentgrass tees. Poa annua contamination of 8.3%, 16.4% and 23.3% was visually estimated in Piranha, Flagstick, and Penncross tees respectively. The perennial ryegrass (RPR) tee was also contaminated with Poa annua.

For next year, we are planning to do research that uses selective herbicides in our tees with contamination. For example, the selective herbicide Tenacity could be used to reduce creeping bentgrass in our Kentucky bluegrass tees. Also, the selective herbicide PoaCure could be used to reduce Poa annua in our creeping bentgrass tees.

Final Photo

A double rainbow associated with a thunderstorm south of Elgin, Illinois. Shehbaz Singh, Sep 20, 2022




Written by Derek Settle, PhD & Shehbaz Singh, MS. Mission: Provide science-based turfgrass research and diagnostics to 400+ member golf courses/superintendents.