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Pest management of billbugs in orchardgrass grown in Virginia
Kuhn, William Robert
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The bluegrass billbug (Sphenophorus parvulus Gyllenhal) and hunting billbug (Sphenophorus venatus vestitus Chittenden) have become important pests of orchardgrass (Dactylis glomerata L.) grown in Virginia, causing 40 - 100% stand losses according to a 2005 survey of over 324 ha (800 ac) of orchardgrass. Their sheltered feeding habits combined with a lack of labeled insecticides for orchardgrass make billbug control extremely difficult for this crop. Over two seasons, orchardgrass fields were surveyed for paired feeding holes caused by feeding of the billbug spring adult. Simultaneously, barrier pitfall traps, a standard method for determining the presence of billbugs in orchardgrass, were used to trap billbug adults in the fields. A comparison of these methods using a Wilcoxon sign-ranked test found no significant differences in the time when paired feeding holes were first observed in fields and when billbug adults were first trapped, showing that the methods are equally satisfactory for determining the presence of billbugs in orchardgrass. In addition, temperature data from SkyBit E-Weather® service, which are currently used to alert growers and other interested parties of pertinent billbug activity in orchardgrass, was compared to data from a field-based weather data logger over the two seasons. A comparison of these data showed high coefficients of correlation, indicating a close relationship between these two degree-day collection methods. Therefore, the SkyBit system can continue to be used for the alert system. A field-border application of Metarhizium anisopliae (Metschnikoff) Sorokin strain F52 (Met-52), an entomopathogenic fungus, was evaluated against billbug adults as they enter orchardgrass fields in the spring. Randomized pairs of treated and untreated plots were placed along the edge of an orchardgrass field in studies over two seasons. Plots were monitored for billbug adults using barrier pitfall traps, and billbug adults were checked for Met-52 infection. The Met-52 proved unsatisfactory for controlling billbugs in this study. A field efficacy trial was used to evaluate several insecticides and Met-52 against billbug adults in orchardgrass over two seasons. A randomized complete block design, four insecticide treatments and an untreated control were used in each of two trials. Samples from each treatment plot were dissected and checked for billbug life stages and for injury to orchardgrass plants. In one trial, plants in the Sevin XLR Plus® treatment were found to have a significantly higher percentage of injury to the crowns than all other treatments except Mustang Max. No other significant differences were seen in this study.
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