Progress in the development and implementation of sweet corn IPM has been made in Ohio during the past 5 years, with emphasis on optimal timing of insecticide applications for control of three key pests: European corn borer, corn earworm, and fall armyworm. This project was undertaken in 1993 so that extension work could be done to promote optimal timing of insecticides, and research could be initiated on broadening the sweet corn IPM program to include tactics other than chemical control, specifically the incorporation of biological control.
The extension component of this project encouraged sweet corn growers to begin or to continue using traps to monitor adult populations of corn earworm and European corn borer in order to better choose an appropriate insecticide spray schedule for silking corn. A letter was sent to 54 sweet corn growers asking if they were interested in participating in a trap network. Responses were received from 22 growers, including 20 who wanted to access the weekly trap counts by telephone, and 12 who intended to monitor traps and share their results. Trap network participants were sent a set of 12 pre-stamped pre-addressed postcards; cards were sent in once per week to report the number of moths trapped. Instructions were included on how to use traps and where traps and fresh lures could be purchased. Trap catches were summarized in articles for the weekly 'Ohio ICM Newsletter' and for a recorded telephone message. A notice announcing the message phone number was placed in the 'Ohio ICM Newsletter' along with an invitation for additional growers to participate in trap monitoring. The phone message was updated 12 times between early July and late September. In addition to announcing pheromone trap catches from participating growers, we included catches of European corn borer in blacklight traps monitored on research sites in central and northern Ohio; during part of the season a site in southern Ohio was also included.
The research component of this project addressed the question of whether acceptable pest suppression could be obtained by conservation and enhancement of indigenous generalist predators, either alone or in combination with a microbical insecticide. The predators of interest were the lady beetle Coleomegilla maculata and the insidious flower bug Orius insidiosus. Predator enhancement was attempted by spraying a commercial sugar-protein product designed as an attractant and food supplement for lady beetles, lacewings, and syrphid flies. Relative abundance of pests and natural enemies were assessed weekly and ear quality was assessed at harvest in two experiments, each conducted in an early and a late planting, at both Columbus and Fremont. One experiment evaluated pest infestation with and without conservation and enhancement of natural enemies, using a split-split-plot design; one set of main-plots was predator-attractant spray vs no predator-attractant spray, the second set of main-plots was carbofuran at-planting vs no carbofuran at planting, and four sub-plot treatments were B.t. granules in whorls, permethrin granules in whorls, standard sprays of thiodicarb during silking, and untreated checks. A separate experiment evaluated releases of commercially-reared lacewings for pest suppression; treatments included four variable factors: crop stage when lacewings released (whorl vs silk), release frequency (single vs double), lacewing life stage released (egg vs pre-fed larva), and release rates (2 eggs, 5 eggs, 1 larva, vs 2 larvae/plant). Although weekly scouting data had documented increased natural enemy activity in plots not treated with conventional insecticides, analysis of harvest quality in the first experiment showed significantly lower damage only in plots where conventional insecticide was used during silking; damage was not significantly reduced in plots where the predator attractant was used or where the microbial insecticide B.t was used (Table 1). Data analysis will be completed during winter 1994.
Table 1. Quality of sweet corn harvested after treatments to manage key caterpillar pests by conventional insecticides and by conservation and enhancement of natural enemies.
| Mean % of ears with damaged kernels* | ||||
|---|---|---|---|---|
| Treatment | Early planting | Late planting | ||
| Fremont | Columbus | Fremont | Columbus | |
| Sub-plots: | ||||
| B.t. in whorl | 15 a | 17 a | 71 a | 99 a |
| permethrin in whorl | 16 a | 16 a | 72 a | 97 ab |
| thiodicarb on silk | 9 b | 10 b | 30 b | 37 c |
| untreated | 17 a | 14 ab | 81 a | 90 b |
| Main plots: | ||||
| predator attractant | 13 a | 15 a | 62 a | 78 a |
| no predator attractant | 14 a | 13 a | 65 a | 84 a |
| Main plots: | ||||
| carbofuran | 17 a | 11 b | - | - |
| no carbofuran | 10 b | 17 a | - | - |
| * Within each column and within each treatment group, means followed by the same letter are not significantly different (P < 0.05), least significant difference test. | ||||
Extension Program Implementation:
Pest monitoring results and suggested spray schedules were announced weekly from early July to late September in newsletter articles and on a recorded telephone message. A talk on insecticide spray schedules, including the use of traps, will be given at the Ohio Fruit & Vegetable Growers Congress in February 1994. After a second year of research in the 1994 field season, suggestions for how growers may use natural enemy enhancement will be added to the sweet corn chapter of the Ohio Vegetable Production Guide.
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