Monday, December 10, 2007 - 10:17 AM

Fall soil sampling for predicting spring infestation of secondary soil pests in corn

Timothy A. Jordan, tajordan@vt.edu1, Roger R. Youngman, youngman@vt.edu1, Curt A. Laub, claub@vt.edu1, and Thomas P. Kuhar, tkuhar@vt.edu2. (1) Virginia Polytechnic Institute and State University, Entomology, 216A Price Hall, Department of Entomology, Blacksburg, VA, (2) Virginia Polytechnic Institute and State University, Eastern Shore Agricultural Research & Extension Center, 33446 Research Drive, Painter, VA

A field study was started in fall 2005, which continued through spring 2007, to predict spring infestation levels of secondary soil pests, specifically white grubs (Coleoptera: Scarabaeidae) and wireworms (Coleoptera: Elateridae) in cornfields. Thirty-four post-harvest soybean fields were sampled in fall and spring in several eastern Virginia counties over two years. Current sampling procedures for secondary soil pests are done in the spring prior to planting by visually inspecting a 30-cm2 by 15-cm deep (standard method) volume of soil for white grubs or by using some form of baiting method for wireworms and white grubs. A 20.3-cm2 by 15-cm deep sample (compact method) was evaluated for its potential to correlate to the standard method after a 2.25 weighting factor (the standard method samples 2.25x more volume of soil than the compact method). No significant differences in white grub counts were detected in both fall and spring between the two methods after correcting for differences in sampling volume. Strong correlations were observed between spring and fall pest densities in both years (r=0.91, P < 0.0001; r=0.88, P < 0.0001). In 2006, fields with ≥ 0.9 white grubs per compact method had significantly greater stand and yield benefits in the Poncho 1250 (1.25 mg clothianidin / kernel) treatment when compared to the Poncho 250 (0.25 mg clothianidin / kernel) and untreated control treatments. Because white grubs were abundant and wireworms scarce in comparison, only white grub data were used for analysis.

Species 1: Coleoptera Scarabaeidae Popillia japonica (Japanese beetle)
Species 2: Coleoptera Scarabaeidae Maladera castanea (Asiatic garden beetle)
Species 3: Coleoptera Elateridae Conoderus spp (wireworm, click beetle)