Non-chemical Approaches for…

Non-chemical Approaches for Annual Bluegrass Control in Turf

By Clebson G. Gonçalves, Postdoctoral Researcher and Shawn D. Askew, Ph.D., Professor, Turfgrass Weed Science, Department of Plant Pathology, Physiology, and Weed Science

In recent years, the search for weed control options in turfgrass systems managed organically or pesticide-free has been an increasing focus of turfgrass research. For annual bluegrass (Poa annua), the problem has intensified because of resistance to many once-effective synthetic herbicides. Although there are few products and strategies that are labeled as organic options, the viability, practicality, and efficiency of these alternative strategies for weed control in turfgrass system is poorly understood.

RESEARCH

From a meta-analysis of 500 search returns via google and google scholar, we found that hand weeding, boiling water, flaming, solarization, and shading had a high likelihood of occurring in consumer searches for organic weed control options in ornamental turf. Successful demonstrations of these methods at Virginia Tech and their occurrence on the internet-search meta-analysis led to

field research trials that were conducted during the 2020 and 2021 growing seasons. We sought to access the efficacy for annual bluegrass control and turfgrass response from several control options that don’t rely on synthetic chemicals compared to synthetic standards (Fig. 1). Data on annual bluegrass control and turfgrass injury were collected and analyzed.

FIG. 1. (A) – Aerial photo of the alternative weed control research trial.

FIG. 1. (B) – boiling-water being applied to weedy tall fescue turf (B).

FIG. 1. (C) – flame weed control being implemented on perennial ryegrass turf.

RESULTS

Annual bluegrass can be controlled by alternative methods such as hand removal, solarization, shading, sod replacement, flame, and boiling water. Mature annual bluegrass plants sometimes recovered from flame treatments (Fig. 2). Flame and boiling-water treatments killed all vegetation greater than or equal to the nonselective herbicide glufosinate (Fig. 3), however, tall fescue and bermudagrass recovered from flame and boiling water treatments quickly with acceptable turf cover reestablished in under four weeks. Solarization also controlled annual bluegrass, but injured perennial ryegrass and tall fescue turf greater than 95% in Virginia (Fig. 4 A and B). In Mississippi, collaborator Dr. James McCurdy noted excellent annual bluegrass control as was seen in Virginia, but little to no bermudagrass injury from solarization (Fig. 4 C). Thus, turfgrass response to alternative methods may be speciesdependent. Hand removal and sod replacement injured all turf species the least, but solarization was also among the least injurious to bermudagrass.

FIG. 2. Effect of flaming treatment on annual bluegrass mature plants (A)

FIG. 2.Effect of flaming treatment on annual bluegrass smaller plants (B).

FIG. 3. Tall fescue (A) – subjected to boiling water treatments.

FIG. 3. Tall fescue (B) – subjected to boiling water treatments.

FIG. 3. perennial ryegrass (C) – subjected to flaming treatments.

FIG. 3. perennial ryegrass (D) – subjected to flaming treatments.

FIG. 4. A – Perennial Ryegrass subjected to 8000 watts per square meter solar radiation intensified by clear plastic (“solarization treatment”) immediately after plastic has been removed. Note the light green smooth crabgrass seedlings, brown patches of controlled annual bluegrass, and dark green bermudagrass observed after plastic was removed from bermudagrass treatments.

FIG. 4. B – Tall Fescue subjected to 8000 watts per square meter solar radiation intensified by clear plastic (“solarization treatment”) immediately after plastic has been removed. Note the light green smooth crabgrass seedlings, brown patches of controlled annual bluegrass, and dark green bermudagrass observed after plastic was removed from bermudagrass treatments.

FIG. 4. C – Bermudagrass subjected to 8000 watts per square meter solar radiation intensified by clear plastic (“solarization treatment”) immediately after plastic has been removed. Note the light green smooth crabgrass seedlings, brown patches of controlled annual bluegrass, and dark green bermudagrass observed after plastic was removed from bermudagrass treatments.