Evaluation of Oils and Microbial Pathogens for Control of Lepidopteran Pests of Sweet Corn in New England

Abstract

Vegetable and mineral oil, Beauveria bassiana (Balsamo) and Bacillus thuringiensis subsp. kurstaki Berliner were evaluated for control of Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae), Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in sweet corn (Zea mays L.). Field experiments in Maine and Massachusetts during 1993 and 1994 evaluated oils and pathogens singly or in combinations, using a single application directly to the top of the silk channel, immediately after pollination. Mineral oil alone provided equal (1993) or better (1994) control compared with corn oil. In both years, mineral or corn oil plus B. thuringiensis resulted in 93-98% marketable ears, compared with 48-52% marketable ears in untreated plots. In three factorial experiments with B. bassiana, B. thuringiensis and corn oil, B. bassiana at 5 x 10(7) conidia per ear provided little or no control while B. thuringiensis and corn oil provided significant though not always consistent control of all three species. The combination of B. thuringiensis and corn oil provided the largest and most consistent reduction in numbers of larvae and feeding damage to ears.

Phytotoxicity and Pollination Disorders in Sweet Corn Due to Direct-silk Applications of Materials Used for Alternative Corn Earworm Control

“…At Stillwater in 2003, 96% of the ears harvested from the control plots were infested while the lowest rate, 53% was achieved by application of soy oil + Bt. Our results agree with previous research (Cook et al, 2003(Cook et al, , 2004Hazzard, 2003), indicating that adding Bt to oil treatments applied to the silk channel is more effective for controlling CEW than applying oils alone. The mode of action of the oil is believed to be asphyxiation, while the Bt acts as a stomach poison.…”

“…In these experiments, ears treated with an oilbased material exhibited significantly higher rates of cone-tips than untreated ears or those treated with a carrageenan-based material (Table 3). Previous research noted similar effects (Carruth, 1942;Cook et al, 2003Cook et al, , 2004Hazzard, 2003) but not to the extent found in these experiments. Even when cone-tips were evaluated, the importance of the disorder in assessing marketability was discounted (Cook et al, 2003).…”

“…In the 1940s, mineral oil was used, but, because it is a petroleum product, this material does not meet current organic certification standards (Hazzard, 2003). Recent research has focused on corn and canola oil because as food-grade products, they may be used in organic production.…”

“…Oils applied to corn can damage the plant tissues if applied in a high enough dose (Hazzard, 1998). The efficacy of oil treatments has been demonstrated in some experiments, but phytotoxicity or damage to the developing ear from reduced pollination quality as a result of these applications is not well documented (Cook et al, 2003(Cook et al, , 2004Hazzard, 2003). Early experiments by the authors found up to 88% cone-tip injury due to corn oil + Bt treatments (T.L.…”

Impact of physical characteristics of some mineral and plant oils on efficacy against selected pests

“…While plant spray oils are effective against a range of arthropod pests, when directly compared with mineral oils, their efficacy is generally lower. When applied directly to the new silk at a rate of 0.5 ml per ear of sweet corn, mineral oil was found to reduce Helicoverpa zea numbers more than corn oil (Hazzard et al. 2003).…”