Additional Research Summaries continued
SWEET VERNALGRASS CONTROL with Mesotrione Virginia Tech Researcher: Adam Smith, Graduate Student, and Shawn D. Askew, Ph.D., Associate Professor, Turfgrass Weed Science, Dept. of Plant Pathology, Physiology and Weed Science
weet vernalgrass is a perennial grass common in unmanaged pastures and meadows. Previously, it has not been a weed problem in managed turf systems except in lawns and athletic fields with a high cutting height. However, it easily adapts to new environments and is highly competitive in the spring with a rapid growth rate, early flowering and allelopathic suppressive ability. This year, the Virginia Weed Clinic saw an increase in the number of sweet vernal-
grass samples in lawn-height turf, from both homeowners and sod growers across the state. It was also a problem reported across the Northeast. Sweet vernalgrass is difficult to control in cool-season turf, where we are seeing it as an emerging weed problem. We conducted an experiment to evaluate herbicide options for sweet vernalgrass control in lawn-height tall fescue. We applied seven herbicide treatments at a sod farm near Richmond, Virginia. At 34 days after treatment
(DAT), MSMA at 2.1 kg ai/ha, mesotrione applied once at 0.28 kg ai/ha and mesotrione applied twice at 0.14 kg ai/ha were the best treatments controlling sweet vernalgrass by 73%, 63% and 57%, respectively. (Other treatments included fenoxaprop, quinclorac, amicarbazone, methiozolin and sulfentrazone, but none provided adequate control of sweet vernalgrass.) By 71 DAT, control from MSMA declined to 40%, whereas mesotrione applied twice gave 67% control. A single application at the full labeled rate of mesotrione provided the best control at 100%. No treatment significantly injured or reduced the density of tall fescue. The rapid growth of sweet vernalgrass in spring may explain why a single application of mesotrione performed best. The timing of applications during the most rapid phase of growth will likely pay an important role in the level of control.
DMI Influence on Suppression of ANNUAL BLUEGRASS SEEDHEADS Virginia Tech Researchers: David McCall, Research Associate, Turfgrass Pathology, Dept. of Plant Pathology, Physiology and Weed Science, and Shawn D. Askew, Ph.D., Associate Professor, Turfgrass Weed Science, Dept. of Plant Pathology, Physiology and Weed Science
reduce the impact of annual bluegrass seedheads on golf putting greens, many superintendents apply plant growth regulators (PGRs) to suppress their development. Timing is critical for successful suppression. Common indicators for proper timing are growing degree day models (GDD50) and the blooming of forsythias. These indicators are also useful for timing early season dollar spot applications, which delay the epidemic and slow the rate of development. Demethylation inhibiting fungicides (DMI) are among the most commonly used for this purpose. Several within this group have growthregulating properties, however, which concerns some turf managers about their interaction with PGRs used for seedhead suppression.
We developed a study at the Virginia Tech Golf Course in 2010 to test these interactions. Fungicides included fenerimol (Rubigan), metconazole (Tourney), myclobutanil (Eagle), propiconazole (Banner Maxx), triadimefon (Bayleton) and triticonazole (Trinity). Growth regulators included mefluidide (Embark, Em) and a tank mixture of ethephon (Proxy) + trinexapac-ethyl (Primo Maxx). The timing of application for each was based on GDD50 models, with initial PRGs applied on April 1 and DMIs applied on April 14. In addition to seedhead suppression and dollar spot development, health measurements were collected by visual estimation of turf quality (1â&#x20AC;&#x201C;9 scale) and spectral analysis with normalized difference vegetation index (NDVI), and relative vegetative index (RVI).
28 | VIRGINIA TURFGRASS JOURNAL May/June 2011 www.vaturf.org
As expected, Em was the most efficient at seedhead suppression, but it also resulted in the poorest quality turf for nearly six weeks. Although the Proxy/Primo Maxx tank mixture reduced seedhead development to a lesser extent than Em, it had the highest plant health measurements of all treatments. Though insignificant, there was a consistent trend across five ratings that most DMIs had fewer seedheads than untreated plots. Propiconazole and triadimefon had the greatest reductions. Both NDVI and RVI spectral analysis indicated that of all treatments, those containing Proxy/Primo Maxx had the highest quality, and those containing Em had the lowest quality. Health of all DMIs alone were comparable to untreated plots, with propiconazole and triadimefon trending to the least quality. This study will be repeated in 2011.