Most discussions about compost and pests are concerned with keeping pests out of compost bins. Lots of insects and other pests like to live in a compost bin and I’ll discuss this issue in a future post. But does compost, when added to the garden, reduce the number of pests affecting plants? It is a claimed benefit of compost.
Compost and Insects
When we talk about garden pests we are usually referring to insects. Many insects live in the soil or spend part of their life cycle in the soil so it seems logical that the addition of compost to the soil would affect these pests. However, I could not find any research showing that compost reduces insect attacks on plants.
Since compost improves soil biota ie living things in soil, it seems reasonable that compost would also benefit insects. Healthier soil means more soil life, which means more to eat. Some insects would certainly benefit from this. Compost can be expected to benefit both beneficial insects as well as pest insects. The good thing is that there are more beneficial insects than pest insects, so on the whole, compost should benefit plants by providing homes for beneficial insects—but I have not found much research supporting this idea.
Compost and Nematodes
Nematodes are a type of microscopic worm that lives in soil. There are many different kinds of nematodes. Some are beneficial and infect insect pests, like the June bug, and others infect plant roots and can be a real problem for plants.
There are many studies that show compost decreases nematode populations. There are also some that show nematode populations increase after adding compost. A lot depends on the plants being studied, the type of compost used, and the type of nematode being measured.
As a gardener you can expect that compost will reduce nematode populations. Is it enough to deal with a serious nematode problem? Probably not. If you are applying nematodes to your grass to control grubs you might want keep the compost off the lawn.
Compost Controls Pests
Healthy plants are better able to fight off pest attacks and compost promotes healthy plants. So indirectly, compost is helping reduce problems with pests.
Compost Tea and Pest Control
A lot has been written about compost tea and it’s ability to control pests, but the claims are not supported by the research. See Compost Tea for more details.
1) Innovative uses of Compost – Disease Control for Plants and Animals; http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CCsQFjAC&url=http%3A%2F%2Fwww.epa.gov%2Fcomposting%2Fpubs%2Fdisease.pdf&ei=vfT1VJjnKY_6yASOtYGACg&usg=AFQjCNGroWTek_y7B6zXpTWeWeoyLEpmYw&sig2=B2WeXRxm-WGIY0cIRRts4w
2) Photo Source: BlueRidgeKitties