Host synchrony effects on efficacy and performance of Bt-rootworm traits

Planting date has long been known to affect corn rootworm (Diabrotica spp.) root injury to corn (Zea mays L) and its subsequent impacts on yield.  While not a viable management strategy, planting date can influence corn rootworm population dynamics through larval colonization and survival, adult colonization and subsequent egg laying.  Bt-RW traits alter larval development and delay adult emergence and with it the effects of planting date.  This research was initiated to explore how altered synchrony on Bt-RW trait affects corn rootworm populations.  This study, conducted at Rosemount MN, featured a split-plot design with four planting dates as main effects and three hybrids expressing Bt-RW proteins (none, Cry3Bb1, Cry3Bb1 + Cry34/35 Ab1) as subplots replicated four times.  Data were collected on root injury, corn rootworm adult emergence, lodging and yield.  In this preliminary study, planting date  and hybrid significantly affected all parameters.  As expected, root injury declined with planting date, as did corn rootworm emergence and yield benefits.  Influence of hybrid effects,   its interaction with planting date and its potential effects on corn rootworm population dynamimcs will be discussed.