Earthworm Castings (Vermicompost) Suppresses Insects and Disease

Q. I was reading your blog about worm castings, the chitinase enzyme produced by worms and its ability to control insects. Chitinase has been proven to degrade the chitin that holds insect skeletons together. Chitin is necessary for strong insect exoskeletons. So, using worm castings in garden soils will control insects.

Homemade worm castings from red wigglers in an earthworm bin.

A. Scientists think this may be true about worm castings are vermicompost, but the research hasn’t linked everything together yet. Chitinase occurs in the soil because of earthworms but does this chitinase control insects? Is the soil transferring this chitinase to the plants? Some preliminary research claims it can. The research is going on right now to find out how much value chitinase has controlling problem insects in the garden.

Insect pests controlled

           Studies report that Vermicompost application suppressed 20 – 40% pest problems arising from aphids, mealybugs, cabbage white caterpillars on pepper, cabbage and tomato.

            Gardens are filled with insects. There are good insects and there are bad insects. Can the effects from earthworms only kill the “bad bugs” or will it also kill the “good bugs”? This is why more research is needed.

            This is a similar problem with some of the “organic” insect control chemicals. Soap sprays and oils don’t differentiate between “good bugs” and “bad bugs”. They kill them both. We have to rely on our knowledge about “good bugs” and “bad bugs” and how it might be applied to control only the “bad guys”. 

Plant disease controlled

            There is some evidence worm castings or Vermicompost inhibited some fungal diseases as well as some nematodes in field trials with pepper, tomatoes, strawberries and grapes. It is believed the reason is microbial antagonism. The same effects have been found in manure and compost applications. Sterilizing both of Verma compost, manure and compost removed these effects.

             When only one plant disease was studied, the disease suppression was not as good when the Vermicompost was made from sewage sludge.