Two Bt sweet corn trials were conducted in South Charleston and Wooster in 2021 to determine the efficacy of various Bt gene traits against common lepidoptera (moth) pests such as corn earworm, European corn borer and fall armyworm. Both trials were planted in late June and harvested for evaluation in early September to maximize caterpillar damage. No insecticide treatments were applied to any of the treatments.
Corn earworm filled trap near sweet corn trial.
The South Charleston trial contained two non-Bt hybrids (Providence & Obsession I) and two Bt hybrids (BC0805 & Remedy). There was a fifth hybrid in the trial (Bt traited Obsession II) but it was destroyed by a misapplication of herbicide. In Wooster only Providence (Non-Bt) and Remedy (Bt) were planted.
The primary pest of concern for late planted sweet corn is the corn earworm. There were heavy flights around silking in South Charleston but lighter flights around silking in Wooster. In South Charleston, 98% of Obsession I ears (non-Bt) were damaged, 100% of Providence ears (non-Bt) were damaged, 91% of BC0805 ears (Bt) were damaged but only 0.7% of Remedy ears (Bt) were damaged. In Wooster, 86% of Providence ears (non-Bt) were damaged and 1% of Remedy ears (Bt) were damaged.
Corn earworm caterpillar in ear tip.
It is reasonable to assume that corn earworm would readily damage non-Bt sweet corn ears that were not protected by any insecticide, but why weren’t both Bt sweet corn hybrids (BC0805 and Remedy) protected from damage? The answer lies in the actual Bt traits each hybrid contains; BC0805 is an Attribute I series containing only Cry1Ab genes while Remedy is an Attribute II series hybrid containing Vip3A + Cry1Ab Bt genes. There is general consensus that Cry1Ab Bt genes alone are not protective in sweet corn against lepidoptera pests.
Sweet corn hybrid evaluation underway.
This was the first time any damage had been recorded on Remedy sweet corn in OSU trials. This is important to note because it is a signal that resistance against Vip may be evolving in the CEW population. ECB was not detected in the South Charleston trial and only found in one ear in the Wooster trial. No FAW was found in either trial. Regardless of location within the state, for late planted sweet corn, all hybrids not containing the Vip Bt protein (Remedy/Attribute II) will need to be protected with insecticide sprays to yield relatively worm free ears. Even Vip Bt hybrids may gain some protection from other pests such as stink bugs by adding insecticide sprays.