May Ends! Warm Up Ahead, Broadleaf Weeds, Manuscript Herbicide Research

May began with an unseasonably cool spell, only to swing dramatically into a period of record-setting heat, followed by another drop in air temperatures. This erratic weather pattern has hindered the typical spring growth momentum of creeping bentgrass, which usually begins to thrive under normal May conditions in Chicago. However, the slowdown isn’t solely a May phenomenon; winter desiccation damage has also contributed to thin, off-color putting greens, poor early-season performance, and delayed recovery. As of now, not a single variety in our fairway bentgrass variety trial has reached levels of acceptable visual turf quality, highlighting the cumulative impact of both winter stress and inconsistent spring temperatures.

Image 1. “It’s not snowing, it’s just the cottonwood tree doing its thing.” The fluffy white seed heads are scattered, Eastern cottonwood (Populus deltoides) releasing seeds carried by the wind like midsummer snowflakes across a ‘Flagstick’ creeping bentgrass tee of hole 2, Bob Berry Sunshine Course, Lemont, IL. Singh, May 28, 2025.

From a disease perspective, dollar spot activity has been confirmed in the southern part of Chicago, particularly in Calumet, IL. With warming and moist conditions ahead, further progression of dollar spot disease is anticipated. On the insect front, the first larval instar of annual bluegrass weevils (ABW) have been identified on fairways at two courses we are monitoring in Chicago’s north suburbs. This has coincided well with the half-bloom and half-leaf out stage of eastern redbud trees (Cercis canadensis). Moving forward, scouting for visible yellowing of Poa annua green collars, approaches as well as fairways will indicate ongoing larval feeding and underscores the need for vigilant monitoring and timely control measures. In the meantime, enjoy the summer-like weather. It’s in the forecast!

Weather

As we enter the first week of June, the NOAA weather forecast indicates a high probability of above-normal temperatures. For example, in the Chicago area daily highs are likely to reach the upper 70s to mid-80s. In addition, above normal precipitation is expected, with forecasted totals potentially ranging from 0.5 to 1.0 inches over the period. This combination of warmth and moisture will create ideal conditions for turf disease outbreaks, particularly dollar spot.

Figure 1. A warm-up is likely in Illinois, given a high probability of above-normal temperatures is expected over the next 6–10 days. Chicago, IL. Courtesy NOAA.

Figure 2. Increased rainfall is likely across a majority of the United States including Illinois, given a high probability of above-normal precipitation is forecasted for the next 6–10 days. Courtesy NOAA.

Figure 3. The final week of May exhibited higher maximum temperatures compared to the preceding week, indicating a clear warming trend at Bob Berry Sunshine Course, Lemont, IL.

Figure 4. Daily rainfall for May 2025 totaled 1.89 inches, with most precipitation occurring on May 1, 20, and 28 at Bob Berry Sunshine Course, Lemont, IL.

Scouting for Broadleaf Weeds — Ground Ivy (Glechoma hederacea)

Ground ivy is a creeping perennial broadleaf weed commonly found in golf course roughs and shaded areas of tees and fairways.

Identification

• Square stems, kidney-shaped leaves, and ‘purple’ colored funnel-shaped flowers that appear in spring.
• Spreads aggressively through stolons.
• Thrives well in moist, compacted soils, shady environments, and low-mowed turf with poor drainage.

Chemical Control

Ground ivy is actively growing in spring, making this an ideal time for control. Selective post-emergent herbicides containing triclopyr, or three-way mixtures with 2,4-D, MCPP, and dicamba, are effective when applied during active growth.

Cultural Practices

Can allow for long term suppression of ground ivy.

• Improve sunlight exposure and drainage.
• Reduce compacted soils via cultivation practices.
• Promote dense turf growth via soil fertility management.

For more detailed information on ground Ivy, please refer to the Ground Ivy factsheet by Dr. Aaron Patton, Purdue University.

Image 1. (Left) Ground Ivy close up, and (Right) a dense ground ivy mat formation in a Kentucky Bluegrass rough at Bob Berry Sunshine course, Lemont, IL. Singh, May 28, 2025

Scouting for Broadleaf Weeds — Black Medic (Medicago lupulina)

Black medic is a low-growing annual broadleaf weed commonly found in roughs, fairways, and low-maintenance turf areas.

Identification

• Trifoliate leaves, which are similar to clover.
• Small, bright yellow, button-like flower clusters.
• Spreading growth habit via prostrate stems that root at nodes.
• Thrives in compacted soils, low nitrogen fertility, and in sunny areas.
• Quickly fills drought-prone sites where turf is weak.

Chemical Control

Black medic grows well in late spring through summer, making May to early June a good time for control. Selective post-emergent herbicides containing MCPP, dicamba, 2,4-D, or triclopyr provide effective control.

Cultural Practices

Additionally, cultural practices are also essential for long-term black medic suppression.

• Promote a dense turfgrass stand; black medic does not like shade.
• Maintain adequate nitrogen fertility.
• As needed, provide irrigation during periods of drought.

For more detailed information on black medic, please refer to the Black Medic factsheet by Dr. Aaron Patton, Purdue University.

Image 2. (Left) Black medic close up, and (Right) a dense black medic mat formation in a Kentucky bluegrass rough at Bob Berry Sunshine course, Lemont, IL. Singh, May 28, 2025

Selective Control of Perennial Ryegrass in a Poa annua Tee by Manuscript

A Syngenta-sponsored herbicide study was conducted in 2024 on a tee of hole 3 at the Bob Berry Sunshine Course in Lemont, IL. The effects of different application rates of Manuscript herbicide to selectively remove perennial ryegrass were investigated.

Image 1. A ‘RPR’ perennial ryegrass tee with about 40–50% Poa annua contamination, Bob Berry Sunshine Course, Lemont, IL. Singh, May 28, 2025

Tee Background

During a 2020 renovation project, existing ‘Penncross’ creeping bentgrass turf was killed using the non-selective herbicide glyphosate. The dead turf was then, removed with a sod cutter, and was reseeded with new ‘RPR’ perennial ryegrass. Over the past four years, Poa annua has progressively encroached on the tee surface and now is approximately 40 to 50% of the turf composition. This tee also has a low level of creeping bentgrass contamination as well (10 to 15%).

Objectives

• Evaluate different application rates to selectively remove perennial ryegrass.*
• Evaluate any associated phytotoxicity.
• Evaluate residual effects.
• Evaluate effects on Poa annua and creeping bentgrass

*Ryegrass is often unintentionally introduced through divot repair mixes containing ryegrass seed on tees and fairways. Our objective is to evaluate the effectiveness of Manuscript herbicide in controlling or preventing ryegrass contamination in such situations on a golf course.

Materials and Methods

• A study was conducted using seven treatments with four replications.
• A randomized complete block design (RCBD) was implemented with four blocks in total. Two are located on the north side and two on the south side of the tee surface. The tee areas receive part shade.
• Individual plot size is 4 ft x 6 ft.
• Treatments were applied using a CO2 backpack sprayer at 40 psi with three XR TEEJET 800 VS nozzles. Applied in water equivalent to 2 gallons per 100 sq ft.

Table 1. Treatments used in the selective herbicide study in 2024 at Bob Berry Sunshine Course, Lemont, IL.

Data Collected

• Visual Quality (1–9 scale, with 6 = minimum acceptable and 9 = best)
• Normalized Difference Vegetation Index (NDVI) using GreenSeeker/Trimble HCS-100
• Ryegrass (% per plot)
• Poa Annua (% per plot)
• Creeping Bentgrass (% per plot)
• Brown Discoloration (% per Plot)

Results — Ryegrass Control

• All Manuscript application rates showed some degree of perennial ryegrass suppression.
• Two applications of the Manuscript at 4 fl oz/acre provided the best perennial ryegrass control.
• Residual effects were observed in 2025. Nine months after the initial application, the lowest perennial ryegrass cover was recorded in the treatment with 4 fl oz/acre applied twice. In contrast, other treatments showed a slight increase in perennial ryegrass, possibly due to recovery of previously injured plants or germination of residual seed from the previous year.

Figure 1. Residual effects in 2025 (yellow bar) of Manuscript treatments in a perennial ryegrass tee, Bob Berry Sunshine Course, Lemont, IL.

Brown Discoloration

• A high level of brown discoloration was observed given two applications of Manuscript at 4 fl oz/acre, suggesting a greater herbicidal activity on perennial ryegrass versus other treatments.

Figure 2. Percent Brown Coloration in 2024 of Manuscript herbicide treatments in a perennial ryegrass tee surface, Bob Berry Sunshine Course, Lemont, IL.

Percent Poa Annua and Creeping Bentgrass

• The levels of Poa annua and creeping bentgrass in treatment plots were unaffected by Manuscript applications in 2024.
• The 2025 residual evaluation revealed an increase in both Poa annua and creeping bentgrass following the suppression of perennial ryegrass.
• This study demonstrates the capability of Manuscript herbicide to selectively remove perennial ryegrass without negatively impacting two other turfgrass species (Poa annua and creeping bentgrass).

Figure 3. Percent Poa Annua in Manuscript herbicide treatment plots in a perennial ryegrass tee surface, Bob Berry Sunshine Course, Lemont, IL.

Figure 4. Percent Creeping Bentgrass in Manuscript herbicide treatment plots in perennial ryegrass tee surface, Bob Berry Sunshine Course, Lemont, IL.

Visual Turfgrass Quality

• Two applications of Manuscript at 4 fl oz/acre resulted in the poorest overall turfgrass quality during the study period; An artifact caused by its effective control of perennial ryegrass (desired).

Figure 5. Visual Turf Quality in 2024 of Manuscript herbicide treatments in a perennial ryegrass tee surface, Bob Berry Sunshine Course, Lemont, IL.

Image 2. Residual Effects of Manuscript herbicide treatments versus untreated in a perennial ryegrass tee surface, Bob Berry Sunshine Course, Lemont, IL. Singh, May 28, 2025

Education & Communication by CDGA’s Green Committee

A CDGA Green Committee article exploring how trees impact turf health, playability, and course design. Let’s Talk About Trees. Read more articles here: Magazine Articles

Final Photo

Dame’s Rocket (Hesperis matronalis) in full bloom. A spring wildflower often found in woodland edges and roadsides, bears purple flowers during early summer. Black Forest Reserve, Dupage County, IL. Singh, May 26, 2025

“Hesperis matronalis is an herbaceous flowering plant species in the family Brassicaceae. It has numerous common names, including dame’s rocket, damask-violet, dame’s-violet, dames-wort, dame’s gilliflower, night-scented gilliflower, queen’s gilliflower, rogue’s gilliflower, sweet rocket, and mother-of-the-evening.

These plants are biennials or short-lived perennials, native to Eurasia and cultivated in many other areas of the world for their attractive, spring-blooming flowers. In some of those areas, it has escaped from cultivation and become a weed species. The genus name Hesperis was probably given because the scent of the flowers becomes more conspicuous towards evening (Hespera is the Greek word for evening).

In North America, Hesperis matronalis is often confused with native Phlox species that have similar large showy flower clusters. They can be distinguished from each other by foliage and flower differences: dame’s rocket has alternately arranged leaves and four petals per flower, while phloxes have opposite leaves and five petals.” For more see Wikipedia