Author
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MITCHELL, EVERETT |
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HU, GUANGYE - ENT. DEPT., UNIV. OF FL |
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JOHANOWICZ, DENISE - ENT. DEPT., UNIV. OF FL |
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Submitted to: HortScience
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/1/2000 Publication Date: 8/1/2001 Citation: N/A Interpretive Summary: Cruciferous vegetables are important crops throughout the world. The diamondback moth (DBM) has become the most destructive pest of crucifers with management costs reaching approximately $1 billion annually. The DBM is difficult to control, in part because it has developed resistance to many insecticides, including biologicals such as Bt in some populations. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, have developed a simple, yet practical method to combat DBM in cabbage that greatly reduces reliance on conventional pesticides. The system is based upon the insects' propensity to deposit their eggs on cabbage plants along field margins as they enter. Observation indicated that DBM females prefer collard greens over cabbage plants to deposit their eggs. Collard greens were planted around the edges of the fields to intercept incoming moths. The DBM continued to cycle in the collard greens throughout the cabbage season. Large numbers of a native parasite, Diadegma insulare, built up in the collards and helped keep the DBM population in check. This was tested over a 2-year period on several farms in northeast Florida. Growers using the trap crop system sprayed on average 56% less than growers who used conventional spray programs. Several of the sprays in the trap crop acreage were for cabbage looper which has re-surfaced in the area as a recurrent pest of cabbage. Based upon cost of insecticides, growers' using the trap crop system saved $46-62 per acre in material costs alone without sacrificing yield or quality. This shows that biological tactics can be used to control DBM in cabbage, greatly reducing pesticides in the environment, improving worker safety and decreasing pesticide residue on the harvestable product. Technical Abstract: Collard greens (Brassica oleracea var. acephala L.) were planted in the peripheries of cabbage (Brassica oleracea var. capitata L.) fields in the spring growing seasons of 1997 and 1998 to evaluate their effectiveness as a trap crop to manage the diamondback moth (DBM), Plutella xylostella (L.). In both years, the numbers of DBM larvae in collards alone exceeded the action threshold of 0.3 total larvae/plant in eight of nine fields. The numbers of DBM alone never exceeded the action threshold in any of the fields that were completely surrounded by collards, but did exceed the action threshold in three of the fields without collards on four sampling dates in 1998. Larval counts in cabbage surrounded with collards were not significantly higher than in the conventionally-planted cabbage, but the number of pesticide applications was reduced in the collard-surrounded fields. The few pesticide applications in fields surrounded by collards likely were used to control cabbage looper, Trichoplusia ni (Hubner), which was not impeded from infesting the interior cabbage by the collards. There was no significant reduction in marketability or increase in damage to cabbage in fields where collards were planted compared to fields where the pest control strategy was the use of conventional pesticides only. The reduced number of pesticide sprays, as well as the high concentration of host larvae in the collards may help maintain populations of diamondback moth natural enemies in the agroecosystem. Planting collards in field peripheries is a potentially effective tactic to manage diamondback moth in cabbage. |
