Friday, June 3, 2011

Pest Alert: Tomato Hornworms!

Now is the time to check your tomato plants for tomato hornworms! These large caterpillars (up to 3" long) can quickly strip a tomato plant of most of if its leaves. This will not kill plants but will definitely set them back. The more leaves that are eaten, the longer it will take plants to recover. Tomato hornworms blend in well with tomato leaves and can be challenging to spot - look for missing foliage and then search the stems for the caterpillars.

If you find them, either squish them (this is rather messy as they are large caterpillars!), drown them in a bucket of soapy water, or spray plants. Do not be afraid to handle the caterpillars - they do not bite or sting (despite the rather dangerous looking horn!). Organic pesticides: B.t. (sold as Dipel and other brands) and Spinosad (sold as Captain Jack's Dead Bug Brew and other brands) - both are effective for caterpillar control. Spray late in the evening as these products break down quickly in sunlight. Conventional pesticides: Sevin (carbaryl), permethrin, bifenthrin - be sure to check the label for the pre harvest interval (# of days you have to wait after spraying before harvesting).

These pests have come out early this year, in part due to the early hot weather. They hatch from eggs laid by a type of sphinx moth and will continue to be a problem all summer and into the fall so you will have to keep scouting for these pests all season.

If you find caterpillars that appear to be covered in white, cigar shaped cocoons leave them in your garden! They have been parasitized by the braconid wasp, a very small beneficial wasp that does not sting people or harm plants. More beneficial wasps will hatch from the cocoons and infect other caterpillars, providing natural control for this pest. 

Hornworm parasitized by beneficial wasps

Learn more!


1 comment:

  1. Thought I would share this article about organic control of hornworms and grubs: