Monday, December 11, 2006 - 8:47 AM

Evaluation of fall soil sampling for predicting spring infestation of secondary soil pests in corn

Timothy A. Jordan,, Roger R. Youngman,, Curt A. Laub,, Thomas P. Kuhar,, and Siddharth Tiwari, Virginia Polytechnic Institute and State University, Entomology, 216-A Price Hall; MC-0319, Department of Entomology, Blacksburg, VA

A field study was started in fall 2005, and continued in spring 2006, to predict spring infestation levels of secondary soil pests, specifically white grubs (Coleoptera: Scarabaeidae) and wireworms (Coleoptera: Elateridae) in cornfields. Fifteen post-harvest soybean fields were sampled in late October and early November, and again in late March in several eastern Virginia counties using a randomized complete block design with 15 replicates (paired t-test). 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 annual white grubs or by using a baiting method for wireworms and annual white grubs. A 20.3-cm2 by 15-cm deep sample method was evaluated for its potential to correlate to the standard method after a 2.25 weighting factor (the standard method samples 2.25 x more volume of soil than the 20.3-cm2 by 15-cm deep method). No significant differences were detected in both fall and spring between the two methods after correcting for differences in sampling volume. Fall 2005 and spring 2006 sampling, respectively, indicates abundant white grub densities ranging from 0.9-10.1 and 0.4-6.8 grubs per standard method. Wireworms averaged less than 1 wireworm per standard method. In fall, 12 fields exceeded the economic threshold of 2 grubs per standard method, and in spring, 8 fields. In all fields, the fall and spring pest densities will be evaluated against corn grain yield loss in a control and two insecticide seed treatment rates, low and high.

Species 1: Coleoptera Elateridae (wireworm)
Species 2: Coleoptera Scarabaeidae (white grub)

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