Mid-May! Research Begins, White Clover, and Velocity vs Poa Annua
As we move into the second week of May, the CDGA turfgrass research season is officially underway. A new silvery thread moss control study was initiated on the nursery green at North Shore Country Club in Glenview. It will build on previous research which has looked at alternative way to control moss in putting greens. At the Bob Berry Sunshine Course in Lemont, a broadleaf herbicide trial has been initiated in a Kentucky bluegrass rough that is predominately white clover. The aim is to help determine the optimal application timing in situations where white clover is especially difficult to control.
In a week, turfgrass scouting has revealed the growing season is progressing. On the north side of Chicago a new pest called annual bluegrass weevil (ABW) continues to be detected in both Poa annua fairways and putting green collars. Turfgrass weed pressure is also increasing. For example, White clover (Trifolium repens) is now more apparent in fairways and roughs and teasel (Dipsacus sp.), an invasive biennial broadleaf weed, is in its juvenile stage. Now that it’s mid-May, golf courses have begun to adjust their cultural practices on putting greens. It’s called “grooming”. Grooming uses a reel mower equipped with narrow blades on close spacing. Considered an important practice for encouraging upright turfgrass growth and improving surface smoothness. Hey, it sounds like it’s time to enjoy some smooth greens this spring!
Weather
Grooming
Grooming removes laterally growing leaves or stolons with minimal surface disruption and limited organic matter removal, making it a suitable practice to perform frequently throughout the growing season. In contrast, vertical mowing is a more aggressive practice that removes accumulated thatch and organic matter, resulting in noticeable surface disruption. As a result, verticutting is typically limited to just a few times per year. More detailed information on grooming and related practices can be found here. USGA Green Section Record. Vol. — 61, Issue — 08. Grooming, Verticutting and Vertigrooming: Similarities, Differences and Keys to Success.
Scouting for Weeds — White Clover (Trifolium repens)
White clover is a low-growing creeping perennial broadleaf weed. It is commonly found on golf courses, particularly in fairways, tees, and roughs.
- Spreads via stolons.
- Easily identified by its trifoliate leaves with characteristic white V-shaped markings.
- Thrives in moist, compacted soils and areas with low nitrogen fertility conditions.
- Often found in high-traffic or low-maintenance turf zones.
- Disrupts surface uniformity, visual quality, and will interfere with ball roll on closely mowed turf areas.
White clover is actively growing in mid-May, making this an optimal timing for control. Selective post-emergent herbicides containing 2,4-D, dicamba, or MCPP are effective when applied under favorable conditions, such as moderate temperatures and no rainfall for at least 24 hours.
Additionally, cultural practices are also essential for long-term white clover suppression. Two aspects are helpful.
- Maintain adequate nitrogen fertility.
- Promote a dense turf.
For more detailed information on white clover, please refer to the White Clover factsheet by Dr. Aaron Patton, Purdue University.
Selective Control of Annual Bluegrass (Poa Annua) in Creeping Bentgrass Tee Surface by Velocity PM
A Nufarm-sponsored herbicide study was conducted in 2024 on hole 3 ‘Tee I’ at Bob Berry Sunshine Course in Lemont, IL. The residual effects of different application rates of Velcity PM in suppressing Poa annua will be shared below.
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 ‘Penncross’ creeping bentgrass. Since this tee remains shaded for most of the day, it resulted in reduced bentgrass turf density. Over the past four years, Poa annua has progressively encroached on the tee surface; now approximately 40 to 50% of the turf composition.
Objectives
- Evaluate different application rates in suppressing Poa annua.
- Evaluate any associated phytotoxicity.
- Evaluate residual effects.
Materials and Methods
- A study was conducted using four treatments with four replications.
- For demonstration purposes, the 4 replications of a particular treatment were grouped together.
- Individual plot size was 4 ft x 6 ft, with the whole study area measuring 6 ft x 16 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.
Data Collected
- Visual Quality (1–9 scale, with 6 = minimum acceptable and 9 = best)
- Normalized Difference Vegetation Index (NDVI) using GreenSeeker/Trimble HCS-100
- Poa Annua (% per plot)
- Creeping Bentgrass (% per plot)
- Phytotoxicity (% per plot)
Results — Poa Annua Control
- All Velocity PM application rates effectively suppressed Poa annua over the course of the study.
- Residual effects were seen in 2025. One year from initial application, Poa annua contamination was lowest in low rate (0.75 fl oz) plots, while a resurgence of Poa annua was observed in both medium rate (1.5 fl oz) and high rate (4.5 fl oz) plots.
Visual Quality
- Low Rate (0.75 fl oz — 5 Apps) After the first application on 13 May = saw least decrease in visual turf quality (Figure 4A).
- Mid Rate (1.5 fl oz — 3 Apps) and High Rate (4.5 fl oz — 1 App) Both of these treatments saw a gradual decrease in visual turf quality after the first application on 4 June and 15 June, respectively (Figure 4B).
- Mid Rate (1.5 fl oz — 3 Apps) = saw largest decrease in visual turf quality (Figure 4C).
Education
Visit the CDGA Turfgrass Program website for updates on ongoing research trials and peer-reviewed publications. The site also features a collection of turfgrass articles and educational videos, offering practical insights for superintendents, researchers, and turf professionals.
Final Photo
Carl Linnaeus first described the genus Allium in 1753. The generic name Allium is the Latin word for garlic, and the type species for the genus is Allium sativum which means “cultivated garlic”. The decision to include a species in the genus Allium is taxonomically difficult, and species boundaries are unclear. Estimates of the number of species are as low as 260, and as high as 979. For more see Wikipedia.
