Research Articles continued
EFFECTS OF TENACITY AND DRIVE on Tall Fescue and Bluegrass Establishment Virginia Tech Researchers: Jeffrey E. Derr, Ph.D., Professor of Weed Science, and Adam E. Nichols, Research Assistant, Virginia Tech’s Hampton Roads Agricultural Research and Extension Center, Virginia Beach Sponsors: The Virginia Turfgrass Foundation and The Virginia Agricultural Council
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rowing cool-season turfgrasses in the transition-zone climate of southeast Virginia in the summer is a challenge. While tall fescue (Festuca arundinacea) establishes fairly quickly and has both the heat and drought tolerances to survive these summers, its susceptibility to brown patch (Rhizoctonia solani) presents a major problem in home lawns or other turf areas. Kentucky bluegrass (Poa pratensis) has very desirable characteristics and is not susceptible to brown patch, but it has poor heat and drought tolerance. Kentucky bluegrass is also slow to establish, resulting in weed encroachment that leads to density and uniformity problems. With the release of the new hybrid bluegrasses (Poa pratensis x arachnifera), the desirable characteristics of Kentucky bluegrass have been matched with the heat tolerance of Texas bluegrass. However, the hybrid bluegrasses establish slowly, leaving new plantings susceptible to weed encroachment. Until the introduction of Drive (quinclorac), the only preemergence herbicide option at the time of seeding cool-season turf was Tupersan (siduron). Drive (quinclorac), however, cannot be used at seeding time of Kentucky bluegrass. Tenacity (mesotrione) has recently been introduced for use in seeded and established Kentucky bluegrass and certain other cool-season grasses. Tenacity controls a range of annual broadleaf weeds and, thus, will be of benefit when seeding slowestablishing turf species such as Kentucky bluegrass. Tenacity may also have utility in hybrid bluegrass.
This study examined the effects of Drive, Tenacity and the combination of the two herbicides on the establishment of tall fescue, Kentucky bluegrass and four hybrid bluegrasses.
Our research ‘Greenkeeper’ tall fescue, ‘Midnight’ Kentucky bluegrass and ‘Solar Green’, ‘Dura Blue’, ‘Thermal Blue’ and ‘Thermal Blue Blaze’ hybrid bluegrasses were seeded on October 14, 2008. The tall fescue was seeded at 6 lbs./1,000 ft2, while all of the bluegrasses were seeded at 2.25 lbs./1,000 ft2. Fertility was applied at the time of seeding at a rate of 0.75 lbs. N/1,000 ft2 from an 18–24–12 fertilizer. Fertilizer applications were repeated three more times in November, March and May. Trimec Classic was also applied in May to remove uncontrolled broadleaf weeds. Treatments were applied the day after seeding. Tenacity was applied at a rate of 0.25 lb. active ingredient/ acre. Drive was applied at a rate of 0.75 lb. ai/acre. The combination was applied at the individual rates. Percent turf cover and percent weed cover were rated periodically from December through May. We have continued to maintain these plots, allowing us to determine long-term persistence of these cultivars. We repeated the entire trial in the fall of 2009.
Research results By the beginning of December in the first trial, the faster-establishing tall fescue had 86% cover in the control and Tenacity plots (Table 1). All of the
22 | VIRGINIA TURFGRASS JOURNAL May/June 2011 www.vaturf.org
bluegrasses were at half of the cover of the tall fescue in the untreated and Tenacity plots. All plots receiving Drive and the combination of Drive plus Tenacity had far less turf cover, especially in the bluegrass plots. The lower turf cover was due to noticeable stunting of growth by the Drive component. Due to the lack of parsely-piert (Alchemilla microcarpa) control, potentially combined with increased weed encroachment due to lower turf cover, plots treated with Drive alone had as much weed cover as the untreated plots in February (Table 2). At this same time, the Tenacity and Tenacity plus Drive treated plots were nearly weed-free. We observed excellent preemergence control of hairy bittercress, henbit, common chickweed, cudweed and parsley-piert with Tenacity at three months after treatment. By April, turf cover in all species, for both untreated and Drive plots, were lower than the December ratings due to high weed cover. The Tenacity plots had greater turf cover than the Drive and untreated plots, but they did have a large amount of white clover (Trifolium repens), while the Tenacity plus Drive plots remained nearly weed-free. At this time, the hybrid bluegrasses had less turf cover than tall fescue in the Tenacity plots. Following a Trimec Classic application in early May to remove broadleaf weeds, another turf cover rating showed how much turf was underneath the weed cover. The untreated and Tenacity plots in all the species had greater than 90% cover. The Drive