Research Articles continued
Cover Story
Sweet Vernalgrass Control in Cool-Season Turf
Virginia Tech Researchers: Adam Smith, Graduate Student, and Shawn D. Askew, Ph.D., Associate Professor, Turfgrass Weed Science, Plant Pathology, Physiology & Weed Science Dept. Research Cooperators: Brookmeade Sod Farm, Inc.
S
weet vernalgrass (Anthoxanthum odoratum) is a new weed concern in Virginia for cool-season turfgrass. A perennial grass weed that can easily adapt to new environments, it is highly competitive in the spring due to its rapid growth, early flowering and potential allelopathic suppression (of desirable turf). Its light green color also decreases turf aesthetics. In recent years, sod producers, homeowners and golf course superintendents have seen an influx in sweet vernalgrass. Additionally, the Virginia Tech Weed Clinic, which identifies and provides control recommendations to individuals who send in weed samples, has documented a drastic increase in the number of sweet vernalgrass samples being submitted. Herbicides are typically the most realistic option for controlling perennial weeds in established turf. Unfortunately,
Photo 1: Mature sweet vernalgrass with seedhead.
control options for sweet vernalgrass in turfgrass are unknown due to a lack of research studies. The objectives of this research are to determine sweet vernalgrass control options with herbicides in cool-season turf with minimal turf injury. Experiments explored herbicide efficacy, rate and timing recommendations for sweet vernalgrass control for the purposes of maximizing herbicide sustainability and turf health.
Our research
We established our field studies on a commercial sod farm in Richmond, Virginia, in mature tall fescue turfgrass infested with sweet vernalgrass. Eight herbicide treatments were applied two different sweet vernalgrass growth stages: at plant emergence and at 2to 3-tiller growth stages. Treatments included mesotrione, fenoxaprop, ambicarbazone, quinclorac, MSMA, methiozolin and sulfentrazone. These herbicides reflect multiple herbicide modes of action, including ACCase
inhibitors, PPO inhibitors, HPPD inhibitors, synthetic auxins and photosystem II inhibitors.
Preliminary results
Preliminary results suggest that mesotrione may be the only option for sweet vernalgrass control (Photo 2 and Figures 1 and 2), since the EPA has cancelled all agricultural uses of MSMA (including turfgrass). Results also suggest that there may be a differential rate need for mesotrione based on application timing. Sequential applications of mesotrione may be required if control regimens are initiated at plant emergence, and a single application may be needed if control regimes are initiated at the 2to 3-tiller growth stage (Photos 1 and 2). Research currently underway will confirm this differential rate need. Understanding how mesotrione application timing and plant growth stages may affect herbicide rate need will provide important information that will lead to sustainable and economical use of mesotrione. c
Photo 2: Mesotrione (right) control at 71 DAT, compared to a non-treated check (left).
22 | Virginia Turfgrass Journal May/June 2012 www.vaturf.org