Research Articles continued
MAINTENANCE PRACTICES that Influence BROWN PATCH and WEED ENCROACHMENT IN TALL FESCUE Virginia Tech Researchers: Matthew Cutulle, Graduate Research Assistant; Jeffrey F. Derr, Ph.D., Professor of Weed Science; and Adam E. Nichols, Research Assistant (all at Virginia Tech’s Hampton Roads Agricultural Research and Extension Center, Virginia Beach); David McCall, Turfgrass Pathologist (Virginia Tech, Blacksburg); with Brandon Horvath, Ph.D., Assistant Professor of Plant Pathology (University of Tennessee, Knoxville) Sponsors: The Virginia Turfgrass Foundation and The Virginia Agricultural Council
Tall
fescue is one of the most commonly grown turfgrasses for home lawns and other lowermaintenance turf areas in the United States. Tall fescue’s popularity is attributed to a deep root system (drought tolerance), relatively low nitrogen requirements and a resistance to most diseases. However, one pest in tall fescue is the fungal pathogen Rhizoctonia solani, which infects tall fescue stands during hot, humid conditions when tall fescue is already under summer stress. The subsequent disease, brown patch, is aesthetically unpleasing and can thin out the turfgrass stand, leading to the germination and encroachment of winter annual weeds such as annual bluegrass and summer weeds such as crabgrass. We have been investigating the impact of maintenance practices on brown patch and subsequent weed infestations. Typically, tall fescue is overseeded in the fall, so applying preemergence herbicides to control annual bluegrass is not an option. Currently, there is no postemergence herbicide option for controlling emerged annual bluegrass in tall fescue in the spring. One potential postemergence herbicide for control of annual bluegrass in tall fescue, however, is bispyribac-sodium (Velocity). Unfortunately, preliminary reports indicate that applications of
bispyribac-sodium to cool-season grasses increase susceptibility to brown patch, thus promoting the consequential increase of summer disease and fall weed encroachment. Chitinase activity is positively correlated with resistance to R. solani in rice; thus, if applications of bispyribacsodium reduce chitinase activity in tall fescue, it may be responsible for increased brown patch. Hybrid bluegrass may be an alternative grass to grow in the transition zone. Hybrid bluegrass cultivars have been developed from crosses between Kentucky bluegrass (Poa pratensis) and Texas bluegrass (Poa arachnifera). Hybrid bluegrass has the desirable qualities of Kentucky bluegrass (i.e., color, quality and brown patch resistance), but it was bred to have increased heat and drought tolerance. However, hybrid bluegrass requires more fertility and may not establish as quickly as tall fescue. Our hypothesis is that combining hybrid bluegrass (which is resistant to brown patch) with tall fescue (which establishes quickly) will reduce overall disease severity and weed encroachment, thus leading to reduced fungicide and herbicide inputs while maintaining turf quality.
Impact of mowing and fertilization scheduling In ‘RTF’ tall fescue, we evaluated 2
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mowing heights (2.5" and 4"), 3 levels of fertility (1, 3.5 and 4.5 lbs. of nitrogen per 1,000 ft2 annually) and Ronstar G (oxadiazon) application versus no preemergence crabgrass herbicide. Three common bermudagrass plugs (4" in diameter) were transplanted to each plot. We measured bermudagrass diameter, brown patch disease severity and turf quality over time. The experiment was conducted twice in Virginia Beach, once in Blacksburg and once in Knoxville.
Results Plots that did not receive Ronstar had significantly more southern crabgrass than the plots that were treated. Crabgrass became so severe in the plots mowed at 2.5" with no Ronstar that it outcompeted both tall fescue and common bermudagrass. When plots were treated with Ronstar, mowing at 2.5" resulted in greater bermudagrass spread compared to plots mowed at 4" when averaged across all levels of fertility (see Table 1). There seemed to be a trend for increased bermudagrass growth with increased fertility in the 2.5" mowing height. For the 4" mowing height, the reverse was true — increased fertility lead to decreased bermudagrass encroachment. Mowing at 2.5" with high fertility resulted in significantly more brown