Aerial application factors affecting corn earworm control on sweet corn

by

Juan D. Lopez, Jr.

Contact: Dr. Juan D. Lopez, Jr.   e-mail: Juan.Lopez@ars.usda.gov

Summary:

Corn earworms, Helicoverpa zea (Boddie), are a major insect pest of sweet corn.   Although larvae feed on whorls of corn plants, feeding on developing ears is the major concern from a grading and marketability standpoint.  Female moths oviposit primarily on individual corn silks or plant parts such as husks or stems close to where silks will emerge.  Larvae hatch from eggs in about 3 days and burrow into the corn ear through silks at the tip.  Once larvae enter corn ears, they cannot be controlled by insecticides because they are not accessible for insecticidal contact.  Additionally, silks are elongating (fresh) during most of the control window and then dry up after grain pollination occurs; however, females can still lay eggs on dry silks which can result in larval ear infestation.  Thus, the control window extends from oviposition and until larvae eat into ears, a period from shortly before or at silking until about 3 days before harvest  Applications of effective ovicidal and/or larvicidal insecticides are necessary to prevent larvae from hatching or to kill larvae after hatching and before ear entry.  Thus, application challenges for controlling corn earworm on sweet corn are many.  Among these challenges are selection of effective ovicides or larvicides, appropriate application timing to maintain control over the control window period, pattern of insecticide deposition on corn ears/silks to deliver a toxic dosage, and a long or known residual control period.  Selection of an effective ovicidal or larvicidal insecticide is complicated by development of resistance through repeated exposure to the same insecticide or insecticides with similar modes of action of eggs or larvae through several generations in sweet corn or other crops.  Collaborating with the Olathe Flying Service at Olathe, CO who initially brought control problems to our attention, we have been conducting research on various aspects of corn earworm control on sweet corn for the past 4 years with emphasis on aerial application.  Among aspects researched are: pattern of captures in sex pheromone traps during the sweet corn production period, initial glass vial bioassays of adults emerging from larvae collected from sweet and field corn, season-long bioassays during 2 years of male corn earworms captured in sex pheromone traps to monitor insecticidal toxicity, evaluation of ovicides in dip or spray table bioassays, number of larvae entering ears as affected by spray rates, pattern of deposition on silks and timing of applications of different ovicides and larvicides on a spray table, and preliminary assessment of aerial field applications of spinosad (Spintor^TM ) for deposition and efficacy on field corn.  All these aspects will be discussed in the presentation with emphasis on the development of an efficient and sustainable aerial application control program for corn earworm on sweet corn.

Manuscript not available online; please contact author for manuscript information.

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