Virginia Turfgrass Journal - May / June 2010

Page 24

Additional Research Summaries


a New Fungicide

Virginia Tech Researcher: David McCall, Research Associate, Dept. of Plant Pathology, Physiology and Weed Science, and Adam Nichols, Research Assistant Sponsor: Petro-Canada


mong the new fungicides released for use in turfgrass in 2009, one of the products that we have been questioned about the most is Civitas. This product is referred to as a plant defense activator, rather than a true fungicide. As an isoparaffin-based mineral oil, it is reported to trigger Induced Systemic Resistance (ISR) within the plant. To date, we have evaluated Civitas on perennial ryegrass and creeping bentgrass, for control of gray leaf spot and dollar spot, respectively. We are consistently seeing a reduction in gray leaf spot compared with

untreated controls, though our data suggest Civitas should not be used as a stand-alone product during peak outbreaks. Instead, we have had very good results when Civitas is tank-mixed with reduced rates of thiophanatemethyl. Control provided by this combination compares favorably with the high rate of thiophanate-methyl alone. Dollar spot was also reduced considerably on creeping bentgrass fairways with applications of Civitas, according to multiple studies in different locations. Results have been inconsistent regarding possible synergism with propiconazole.

Overall, we see this product as having a nice fit into disease-management programs when used correctly. Our research suggests that Civitas does not provide acceptable control alone during peak periods for disease development, but rather used early and late in the season and tank-mixed with low rates of common fungicides. Civitas appears to be safe on both perennial ryegrass and creeping bentgrass when applied during cooler weather, but we caution against making applications in the peak of summer stress. Our research, along with several others’, suggests that tank mixture with chlorothalonil may be antagonistic and cause excessive injury to the turf. On the other hand, it appears to be a nice tank-mix partner with several other fungicides, including propiconazole and thiophanate-methyl. We will continue to update our recommendations on this product as we learn more about its activity against other diseases and safety to various turfgrasses.

INTERACTION OF MOWING HEIGHT, FERTILIZATION AND PREEMERGENCE HERBICIDE APPLICATION on Bermudagrass Encroachment and Brown Patch in Tall Fescue Virginia Tech Researchers: Matthew Cutulle, Graduate Research Assistant; 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), with Brandon Horvath, Ph.D., Assistant Professor of Plant Pathology (University of Tennessee) Sponsors: The Virginia Turfgrass Foundation and The Virginia Agriculture Council


Virginia Tech’s AREC in Virginia Beach, we are conducting research on the impact of mowing height, fertility levels and applications of preemergence herbicide on bermudagrass encroachment and brown patch severity in tall fescue. Ideally, we will be able to determine a fertility/mowing height combination that will reduce bermudagrass encroachment and disease severity while maintaining optimum aesthetics. Research plots containing ‘RTF’ tall fescue were subjected to treatment combinations of two mowing heights (2.5" and 4"), three levels of fertility (1, 3.5 and 4.5 lbs. of nitrogen per 1,000 ft2 annually) and application

(or not) of a preemergence herbicide (oxadiazon). Plugs of common bermudagrass plugs were transplanted to each plot. Plots that received oxadiazon had significantly less crabgrass than the control plots. In the 2008 trial, crabgrass became so severe in the plots mowed at 2.5" with no oxadiazon that we did not get a complete data set for bermudagrass diameter because of crabgrass competition. For the 2009 trial plots that received oxadiazon, mowing at 2.5" resulted in greater bermudagrass diameter (encroachment) compared to plots mowed at 4", when averaged across all levels of fertility. Additionally, we saw an interaction of mowing height and fertility on both


bermudagrass spread and brown patch severity. Mowing at 2.5" with high fertility resulted in the largest bermudagrass spread. There seemed to be a trend for increased bermudagrass growth as fertility level increased at the 2.5" mowing height. For the 4" mowing height, the reverse was true — increased fertility led to decreased bermudagrass encroachment. Mowing at 2.5" with high fertility resulted in significantly more brown patch than any other treatment combination. Overall mowing at 4" resulted in better visual quality, and we recommend this mowing height with the use of a preemergence herbicide when maintaining tall fescue turf.

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