Effect of European Corn Borer on Corn Whole-Plant Yield and Forage Quality
Building on the results of our 2004 preliminary study, a similar field study was conducted in 2005. The overall objective of this study was to determine the effect of different levels of European corn borer (ECB) infestation on whole-plant yield and forage quality of corn grown for silage. The experimental design consisted of a split-plot randomized complete block design, with blocks being replicated eight times. Each block consisted of three main plots with each main plot representing one of the following plant growth stages: 10-leaf, 16-leaf, and blister. Each main plot consisted of 7 subplots with each subplot representing one of the following levels of laboratory reared third instar ECB infestations: 0 (34B23 non-Bt corn), 0 (34B24 Bt corn), 1, 2, 3, 4 and 5 larvae/stalk. Sixteen plants from the middle two rows of each subplot per main plot (i.e., plant growth stage [n=3]) were used for each infestation level. Beginning with the half milkline kernel stage, infested cornstalks were cut manually to record the number of tunnels per stalk. Four complete stalks were selected from each infestation level, and were chopped into approximately 2.5 cm pieces and dried to determine percent dry matter and subsequent forage quality.
ECB infestation level had a significant negative effect on whole plant yield (F = 3.26; df = 5, 24; P = 0.0086), while the main effect of plant growth stage and the interaction between ECB infestation level and plant growth stage were not significant. Of the 5 infestation levels, only the infestation level of 5 larvae/stalk (282.3 ± 10.8 g/stalk) resulted in a significantly lower whole plant yield than the control (315.3 ± 7.5 g/stalk). In addition, plant growth stage and infestation level had no effect on acid detergent fiber (%), neutral detergent fiber (%), and crude protein (%) values.
Objective 1. Determine the effects of European corn borer infestation on whole-plant yield and forage quality of corn grown for silage.
Objective 2. Determine economic injury levels of European corn borer infestations at the 10-leaf, 16-leaf, and blister stages of corn grown for silage.
All of the parameters for the first objective have been successfully met. All yield and forage analysis has been completed and subjected to statistical analysis. Analysis for the second objective is underway, and outcomes are expected by mid-summer.
Impacts and Contributions/Outcomes
Our 2005 results indicate that a significant reduction in whole plant yield occurs at more than 4 ECB larvae per stalk. The importance of this finding is that this level of ECB infestation is rarely found under Virginia conditions (Youngman, unpublished data). Another important outcome of this research concerns the non-significant effect of ECB infestation level on acid detergent fiber, neutral detergent fiber, and crude protein (forage quality parameters). This finding will simplify determining EILs for ECB infestation on corn grown for silage.
Graduate Research Assistant
Virginia Polytechnic Institute and State Univ.
Department of Entomology
216-A Price Hall
Blacksburg, VA 24061-0319
Office Phone: 5402316498