Optimum Timing of an Application of Corn Oil and Bacillus thuringiensis to Control Lepidopteran Pests in Sweet Corn

Abstract

<jats:p>Corn oil and <jats:italic>Bacillus thuringiensis</jats:italic> ssp. <jats:italic>kurstaki</jats:italic> (<jats:italic>Bt</jats:italic>) applied directly into the silk channel of a corn ear has been shown to be an effective pesticide against corn earworm, <jats:italic>Helicoverpa zea</jats:italic> (CEW), and european corn borer, <jats:italic>Ostrinia nubilalis</jats:italic> (ECB). Field studies were conducted in 2000 and 2001 to determine the influence of application timing on ear quality at harvest. Two blocks of corn were planted during each year to observe treatment effects under varying populations of the two insect species. The treatment consisted of 0.5 mL (0.017 floz) of food grade corn oil containing a suspension of <jats:italic>Bt</jats:italic> at 0.08 g (0.003 oz) a.i. per ear applied directly into the silk channel at the husk opening. One treatment application was made on each silk day 3 through 11 from first silk; silk day 1 was the first day that 50% or more of ears had 2.5 cm (1 inch) of silk protruding from the husk. One treatment did not receive the oil + <jats:italic>Bt</jats:italic> suspension. All ears were harvested at milk stage, on silk day 25. The number of CEW larvae in treated ears increased with later application days in 2000, but not in 2001. Damage from larval feeding was mainly found near the tip of the ear, and damage ratings were lower compared to untreated ears for all treatment days for both plantings in 2000, and through application day 8 in the late planting of 2001. ECB larvae were reduced for all treatment days in both plantings in 2000 and the late planting of 2001. The percentage of ears rated as marketable (i.e., free of feeding damage) ranged from 71% to 100% in treated plots compared to 30% to 77% in the untreated plots. There was a linear decrease in marketability with later application days in two of the four plantings. The greatest decrease in marketability was after application day 7. Because the oil application affects kernel development at the tip, the length of ear with under-developed kernels, or cone tip, was measured. The number of ears with cone tip decreased linearly with the later application days in all plantings. There was 10% conetip or less after day 7 in 2000 and day 6 in 2001. The best combination of effective insect control resulting in the highest rates of marketable ears with the least degree of cone tip was achieved in this experiment by application of oil + <jats:italic>Bt</jats:italic> suspension on day 7. Year to year variation in the environment would suggest a range from day 6 to 8.</jats:p>

Recurrent Full-sib Family Selection for Husk Extension in Sweet Corn

“…This ubiquity limits the ability to use cultural controls such as crop rotation and increases the pest's adaptability and probability of successful development (Kennedy and Storer, 2000;Olmstead et al, 2016). The oviposition and feeding habits also limit the efficacy of chemical controls (Barber, 1941;Cook et al, 2003Cook et al, , 2004. Plant breeding remains one of the few promising tools for reducing the economic damage caused by corn earworm.…”

“…Corn earworm is an especially challenging pest for organic sweet corn growers, because few effective management strategies are permissible under the National Organic Program (Cook et al, 2003(Cook et al, , 2004Ni et al, 2011). Organic producers are in particular need of breeding for resistance to corn earworm since the advent of transgenic Bacillus thuringiensis cultivars has supplanted classical breeding for earworm resistance.…”

Impact of Applying Edible Oils to Silk Channels on Ear Pests of Sweet Corn

“…Seven decades later, the chemical insecticide sprayings engendered a series of negative consequences for sustainable sweet corn production, including the costs associated with the increasing number of the insecticide applications during a crop cycle, and the increased concerns about human health, and long-term ecological impact of intensive insecticide applications on nontarget organisms in agro-ecosystems. Research in the last few decades has examined alternative pest management tactics, including planting dates , corn husk features (Wiseman et al 1977), and silk maysin level (Waiss et al 1979, Snook et al 1993, as well as the application of edible oils on corn ears with fresh silks (Cook et al 2003(Cook et al , 2004, or by using a mixture of oils with microbial insecticides . The recent studies have used edible oils instead of mineral oils that were used in 1930 Ð1940s in the New England states, because certain mineral oils no longer meet the present food safety standard (Jackson et al 2007).…”

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

“…The Kerr Center for Sustainable Agriculture (KCSA) in Oklahoma and R. Hazzard of the University of Massachusetts Cooperative Extension began conducting experiments in the 1990s using oil silk treatments, combined with Bacillus thuringiensis spp. kurstaki (Bt) products in an effort to develop an organic management technique for CEW on small commercial farms (Cook et al, 2003(Cook et al, , 2004.…”

“…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.…”