Project Number: 3622-21220-005-04
Project Type: Specific Cooperative Agreement

Start Date: Aug 29, 2005
End Date: Aug 14, 2008

Objective:
Increase knowledge on how the western corn rootworm survives transgenic corn. Specifically, seek greater knowledge on how interactions with grassy corn field weeds affect this survival.

Approach:
Hypothesis 1. Giant foxtail density and removal time impact efficacy of Bt corn under field conditions. Experimental Design. We will utilize a factorial treatment arrangement that will include three giant foxtail densities (0, 85, and 220 plants/9.3 m2 (100 ft2)), three giant foxtail removal times (3, 7, and 14 days) after initial detection of egg hatch and the two corn types (Bt corn and its isoline with both containing the glyphosate tolerance gene) replicated five times. Plots will consist of two 3 m rows with 76 cm row spacing and a fill row on either side of the two-row plot. One plot row will be for adult emergence and the other to measure root damage. Plots will be planted using agronomic practices common to corn production in central Missouri, with the exception of herbicides. The study will be repeated for at least two field seasons. We will be evaluating the effects of weed density and removal timing over a natural egg hatch period. Prior to planting of the study we will determine the actual eggs/liter of soil using our egg separating apparatus modified from Shaw et al. (1976). Corn plantings will be timed so that the majority of western corn rootworm egg hatch occurs as near to V2-V3 stage corn as possible. The giant foxtail should be well established at this time. Typically this occurs around June 1 in Central Missouri. Hypothesis 2. When alternate hosts are available, increasing WCR larval density enhances weed utilization and subsequent damage and beetle emergence on Bt corn. Experimental Design. We will utilize a factorial randomized complete block design with three factors. The first factor will be three D. v. virgifera egg infestation levels (1000, 3000, and 6000 viable eggs/meter). The second factor will be presence/absence of S. faberi at a density of 85 plants/9.3 m2. The third factor will be the presence/absence of Bt in a commercially available glyphosate-resistant maize hybrid. The experiment will be replicated 4 times. Individual plots will consist of two 5 m rows (one damage row and one beetle emergence row) with 76 cm row spacing planted using agronomic practices common to conventional-till maize production in Missouri at the University of Missouri, Bradford Farms. The site selected for this study will not have a background population of WCR eggs but will be mechanically infested using an egg infesting tractor described by Moellenbeck et al. (1994) infested at prescribed levels above with WCR eggs obtained from French Agricultural Research, Inc, Lamberton, MN. Egg infestation and S. faberi seeding will occur immediately after maize planting. Plots seeded with S. faberi will be thinned to the prescribed density (85 plants/9.3 m2, our plots are 7.6 m2) by individually placing disposable plastic cups over 69 seedlings in each plot and treating with glyphosate. WCR egg hatch will be monitored by daily examination of a Petri dish of eggs from the same lot buried at the infestation depth on-site. Removal of S. faberi will occur 4d after detection of egg hatch at which time maize and S. faberi phenology will be recorded. Weed free treatments will be treated with glyphosate as needed.