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 Post subject: BT for corn worms
PostPosted: Fri Jul 18, 2003 8:14 pm 
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Joined: Wed Jul 16, 2003 5:26 pm
Posts: 4
Location: Midland, Texas
Which type of BT is the most effective for corn worms? BTi, BTk, BTsd??
I've sprayed with BTk, but still have damage from the worms - may not have used it soon enough - because the worms found so far are dead.??
Thanks!


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PostPosted: Sat Jul 19, 2003 6:04 pm 
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Joined: Mon Mar 31, 2003 9:18 pm
Posts: 1093
Location: McKinney,TEXAS
Richard-
Bacillus thuringiensis (Bt) is a naturally occurring, soil borne organism that has gained recent popularity for its ability to control certain insect pests in a natural, environmentally friendly manner. Bacterial agents, like Bt, are effective in controlling insects in the larva stage only. The larva stage in an insect’s life cycle is the stage during which most of the feeding occurs. Since Bt must be ingested to work, the insect must be controlled during the larval stage. The larval stage is the stage in which the insect appears worm or caterpillar-like. The Bt is applied to the foliage of plants infested with larva. If possible, apply the Bt to the underside of the leaf surface for two reasons: 1) Most larvas feed from the underside of the leaf surface. 2) Bt is broken down faster in sunlight. Application to the undersides of the leaf surfaces will prolong Bt's activity. High temperatures do not encourage Bt's breakdown.
After Bt spores are ingested by larvae, they grow and reproduce, meanwhile producing crystalline toxins. The crystalline toxins paralyze the digestive tract of the larvae causing it to cease eating. Death will follow, but time of death can range anywhere from 12 hours to 5 days after ingestion. This depends on the amount of Bt ingested, the size and variety of the larvae and variety of Bt used for control. There are different strains or varieties of Bt available that have been selected for the control of specific insects. Bt variety kurstaki (BTK) controls the European corn borer, tomato hornworms, fruit worms, cabbageworm, cabbage looper, spring and fall cankerworm, spruce budworm, and other caterpillar-like larvae. Bt variety san diego (BTSD) controls early larvae of the Colorado potato beetle. Bt variety israelensis (BTI) controls mosquitoes, black flies and fungus gnats.
Pests such as ear worms and corn borers pose a big problem for organic farmers. Ear worms are found in the tips of corn, while borers chew their way into the side of the husk. Remember, organic insecticides don't work on insect eggs, so worms will continue to hatch even after applying Bt.
Tony M


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PostPosted: Sat Jul 19, 2003 8:18 pm 
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Joined: Tue May 20, 2003 4:33 pm
Posts: 526
Location: parker county, texas
I used the one called Thuricide for corn earworms this year with really good results. I didn't spray the plants, but mixed a small amount of Bt in a bottle of water with a dropper tip and dropped a little in each ear as the silks were starting to form. I would guess it wiped out at least 90 percent of the earworm problems I was having.


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