Comparing agronomic performances of Bt and non-Bt corn hybrids

In the United States, seed treatments (STs) and host plant resistance via plant-incorporated-protectants (PIPs) are the most common strategies for managing insect pests of maize. Both PIPs and STs are reliable management tools when insect pressure is high, but there are concerns regarding the sustainability of current use patterns. Field resistance in target pests to many PIPs has been documented. To slow resistance, planting non-PIP “refuge” maize at pre-established percentages (e.g., 5-20% of total plants) is required by regulatory agencies. Surveys indicate that most growers do not plant refuges in part because they lack confidence in refuge yield potential. In regard to STs, regional soil pest pressures do not seem to justify ubiquitous use – currently all maize hybrids are sold with STs applied. Our aim was to determine whether refuge compliance (i.e., planting non-PIP hybrids) could result in yield loss in Virginia. We conducted two years of field studies across multiple regions to compare performances of PIP and non-PIP maize hybrids, with both low and high rates of STs. Our objectives were to: 1) assess soil insect populations to determine areas where STs are needed; and 2) compare insect injury, plant stand, and yield of PIP and non-PIP maize hybrids, with different rates of STs. We found relatively low insect pressure at all locations with one exception. Hybrids with PIPs performed similarly to their non-PIP counterparts, and we found largely no significant benefit provided by STs in any location.