Vermicompost and Insect Control

Q. I have read that worm castings can be effective in eliminating aphid and white fly infestations. Is it effective on all insects that suck plant juices? What effect do worm castings have on beneficial insects? Are there any special instructions or precautions to be considered when using worm castings around fruit and vegetable plants? 

Our own red wrigglers at work in a custom vermicompost bin

A. You are one up on me on this topic. I have not seen any scientific publications that document this to be true in a general sense. If there are some, I would love to see them. 

There is some work at Ohio State University that showed fewer insect problems on vegetables growing on vermicompost than without it. They focused on something the earthworms left behind called chitinase.

research on vermiculture at Ohio State University

There is some grant money right now for researchers working in this area. There are a lot of unanswered questions like how long can you use it, what does the quality need to be, how much do you need to apply and others. 

Grant money

There is no argument that vermicompost is a great soil amendment and may reduce the need for synthetic pesticide applications. There is some debate about “chitinase” and its effect on some insects. I think you have to be careful about jumping to conclusions on this one.

            If chitinase is effective on insects it will be nondiscriminatory. In other words, it does not know the difference between a good insect and a bad insect.

            Once leaf hoppers have matured and they are hopping around a lot when you pass by them they are difficult to control without conventional "hard" pesticides. I have never heard of worm castings used for anything but a fertilizer. That information about is new to me.

            About the only organic method I know of that does a pretty good job controlling leaf hoppers is Spinosad. However, Spinosad has to be applied when leaf hoppers are immature in the nymph stages. It never totally eliminates them but reduces their numbers considerably if they are applied early enough and the sprays are directed where they are living.

            As an example I have used Spinosad sprays in about May on grapes to reduce leaf hopper numbers. I apply the spray about one week apart for 2 to 3 applications as soon as I see the nymphs on the undersides of leaves.

            I direct the spray upward so that the bottoms of the leaves are covered and then I repeat the spray on the tops of the leaves as well. To my knowledge worm castings have no effect on any kind of insect pests or beneficials. Treat it just as you would compost.