Drying! Growing Roots, CDGA Field Day, Moss, and Dollar Spot Research
We just passed mid-August on the calendar — always a good thing for golf course superintendents and staff. A transition from summer’s hot, humid heat to (hopefully) cooler and drier conditions. However, this week I was reminded at a course visit or two that it is a tricky period. Lower humidity and higher evapotranspiration (ET) rates immediately ask a question, “Did healthy roots survive the gauntlet of midsummer?”. The answer, in a majority of cases, was without wilt and a simple yes. In other cases, especially Poa annua, the answer was not good. A record wet July meant turfgrass areas with poor drainage were going to be especially vulnerable to root loss. The low fronts of putting greens, a simple design that allows for surface drainage, is very likely ground zero of weakest roots. But there’s good news for cool season turf. 1) August 2024 has cooled early; 2) Many golf courses are now poking holes (aerification) earlier; 3) Rapid root growth is about to begin (soil temperature of 50–64 degrees optimal).
As we round this final corner of summer, signs of fall in the landscape have begun. Did you noticed that single branch of a maple tree (Acer rubrum) which decided to jump early with some bright red leaves? The squirrels and I have noticed that a familiar oak tree (Quercus alba) has begun to drop its chestnuts earlier than the rest. For sure, August represents is a period of careful water management. To learn more on all the root-related challenges of August, see the USGA article called Sneaky Wilt. You’ll then understand more as we continue to enjoy this drier weather and some of the best playing conditions this growing season.
Weather
A CDGA Turfgrass Research Field Day with Corteva
Jared Hoyle, PhD
We’ve enjoyed conducting some research this summer with Dr. Jared Hoyle and Corteva. First a launch of Corteva’s newest fungicide Floxcor (fluoxastrobin) in July. Then herbicide trials with GameOn and Defender designed to tackle a range of difficult-to-control weeds. In a white clover study, a single Jul 18 application provided near complete control one month later. For more see below.
Scouting for Weeds — Silvery Thread Moss (Bryum argenteum)
Silvery thread moss is major “weed” in creeping bentgrass putting greens. The advent of newer improved creeping bentgrass varieties has not changed this issue for golf course superintendents. The primary issue that promotes moss establishment continues to be low mowing heights.
Thin Areas Vulnerable
Any areas that have a tendency to scalp and thin green height are prone to moss establishment. Green surfaces designed with undulations are vulnerable to scaping (ridges and knolls commonly scalp). Additionally, clean up laps (green edges) are typically associated with moss — repeat equipment wear thins turf over time.
Alternatives to Herbicides for Silvery Thread Moss Control
We continue to study alternatives to control silvery thread moss on putting greens. In summer 2024, moss development did not pause as it usually does. Instead, unusually wet and cool conditions meant moss continued its growth during the summer season.
Fiesta, a chelated iron product, was found to be effective in 2023. We found the level of moss controlled by Fiesta was similar to our standard, the herbicide carfentrazone (QuickSilver). In 2024, we decided to look at a second rate of Fiesta (full label rate and 1/2 label rate). In August we are now seeing differences we did not expect.
More Information
Managing silvery-thread moss in golf course greens by Zane Raddenbush, Steve Keeley and Lloyd Stark. Golf Course Management, 2015
Preventative control of dollar spot (Clarireedia jacksonii) in a creeping bentgrass fairway by Shehbaz Singh, MS
A study funded by BASF and PBI Gordon is being conducted to evaluate the efficacy of fungicides to preventatively control dollar spot disease, Clarireedia jacksonii, on an established ‘L-93’ creeping bentgrass fairway in play at North Shore Country Club in Glenview, Illinois.
Dollar spot is the most chronic disease of both creeping bentgrass and Poa annua. Both species of cool season turfgrass can be highly susceptible, though newer dollar spot resistant creeping bentgrass varieties are beginning to change that. Dollar spot symptoms are small infection centers which appear bleach white in color. Without fungicide treatment, the infection centers will coalesce into larger patch-like areas.
Material and Methods
This fungicide study has 12 treatments in a randomized complete block design with 4 replications. Individual plot size is 4 ft by 6 ft. All applications began on Jun 3 and were made at 21-day or 28-intervals. Applications every 21 days were made on Jun 4, Jun 24, Jul 15, and Aug 5, 2024.
Objectives
- Evaluate dollar spot control
- Evaluate 21 application interval
- Evaluate turf quality
- Evaluate any phytotoxicity
Measurements
- Visual Quality (1–9 scale, with 6 = minimum acceptable)
- Normalized Difference Vegetation Index (NDVI) using GreenSeeker/Trimble HCS-100
- Dollar Spot (% and number per plot)
- Color/Phytotoxicity (1–9 scale, 9 = best color)
Results — Dollar Spot
Dollar spot disease pressure remained low during June and untreated plots saw low levels (less than 5%) due to dry conditions and relatively cool night temperatures. In July, frequent rainfall occurred and dollar spot disease pressure increased rapidly and untreated plots exceeded 10% plot damage on July 15. Dollar spot disease development continued to progress and untreated plots reached 40% damage by August 12.
Acceptable Control
In general, fungicides were able to keep dollar spot damage below 10% on most rating dates. On Aug 5, when untreated plots saw 32.5% damage, a majority of fungicides were able to provide acceptable control (less than 10% damage by dollar spot). Given peak disease pressure on Aug 12, dollar spot exceeded 10% in certain treatments for the first time (Maxtima 0.4oz, Xzemplar 0.26oz, and BASF Experimental low rate). See Figure 1.
Visual Quality
Visual quality was influenced by dollar spot. All fungicide treatments saw acceptable quality (6.0 or greater) until Aug 5. See Figure 2.
Final Image
“Their range consists of southern Canada south to Georgia, Florida, and Texas. Silvery checkerspots enjoy moist areas such as streamsides. They can also be seen in meadows and forest openings. Larval foods are various asters, including Eurybia macrophylla, Verbesina alternifolia, Helianthus, and Rudbeckia. Adult foods include from nectar from red clover, common milkweed and dogbane.” For more see Chlosyne nycteis — Wikipedia
