North Texas Vegetable Gardeners Blog

caterpillar poop (frass)

Seeing signs that caterpillars (I lazily call them worms) are eating up your vegetable plant?

Before going to the ‘spray to kill’ route, let’s think through a few other options first.

Did you know hornworms glow (iridescent) when a black light is shined on them?  It may feel a little strange to work in your garden at night, but a few trips with a special flashlight might be enough to resolve the problem.

Beneficial wasps – tiny little wasps that kill caterpillars?  That is really a thing!  Keep in mind these little guys are the first to be killed if insecticides are sprayed nearby.

Attract birds – have a small birdhouse and perches near your garden gives birds a place to hang out and watch for food.  Birds love fat caterpillars.

Sacrificial crops – if you have the space plant some plants just for the caterpillars to enjoy.

If you decide to use a pesticide, one of the most environmentally friendly ones is BT, Bacillius thuringiensis.  This is a spray that causes a caterpillar’s digestive system to shut down when eaten.  It only affects caterpillars, so it is considered safe to use since it doesn’t harm other critters.  A few things to keep in mind with this product:

• Timing is important – the caterpillars must be actively eating the part of the plant you can get spray on to.
• BT washes off easily – if it rains after you spray it, it is gone
• BT breaks down in the sunlight.  So it is only effective for a few days.
• It takes a few days for the caterpillars to die after they eat BT.
• Read and follow the instructions on the label