Nicholas Maravell, of Potomac, Maryland found that Bacillus thuringiensis was the most effective of four biological controls he tested for controlling key insect pests in sweet. corn but may not be cost-effective in his situation because of application costs.
Maravell tested four different means of controlling corn borers and earworms: spraying with Bacillus thuringiensis; releasing eggs of Trichogramma pretiosum, a wasp that parasitizes corn ear worm larvae; providing a hospitable environment for predators of these pests, by intercropping his corn with red clover; and planting his corn in the midst of a field of vetch surrounded by natural vegetation to encourage for beneficial.
Mr. Maravell reports that the B. thuringiensis was clearly effective. Twenty percent of the ears in his control plots showed some degree of damage, and another 20 percent were so damaged as to be unmarketable. Treatment with B. thuringiensis cut the incidence of damage in half, but with the cost of the bacteria, the special high-clearance spraying rig, and the labor of application factored in, Mr. Maravell says he thinks it was probably not worthwhile.
Maravell reported that the T. pretiosum did not appear to be notably effective, although there was not an adequate control for this part of the experiement. Mr. Maravell suspects that most of the individuals he released flew off to parasitize other species than the intended targets.
There were many damaged ears in the field surrounded by vetch, but there were also beneficials and he did observe parasitized corn borers. Again, inadequate control makes it difficult to assess. Maravell advises against procedure because the vetch turns brown and dies in July, and thus is no longer a suitable home for the beneficals by the time the corn reaches the silk stage.
The red clover did not compete successfully with the weeds, so its effectiveness at attracting beneficials remains unresolved. However, Mr. Maravell believes there may still be some promise in this technique.