Start in the Soil

Often when we walk into a greenhouse our gaze sweeps across the sea of green and we admire the colors, the light and the variety of plant life. We should however follow the admonitions from Les Mis and ‘Look Down’ to investigate where it all starts. In the soil. There are several pests that inhabit this dark underworld, and using biocontrols for these pests is the cornerstone for many programs.

Hidden away where roots meet earth are several greenhouse pests. Fungus gnats can be a nuisance up above, but down below the larvae tear and chew on roots, causing significant damage. Western Flower thrips pupate in the soil. They are not feeding at this time, but if you can control them during this stage, all the better to stop their exponential growth.

Meet the trifecta of soil-based biocontrol: Nematodes, Strat mites and Rove Beetles. Beneficial nematodes are microscopic roundworms that infect and kill many soil pests (including grubs in lawns). Steinernema feltiae is one of the most widely used and studied beneficial nematodes for biological control. Where do these strange nematode names come from? In this case, Sf is named after two American scientists, Steiner and Felt, who studied nematodes in the 1950’s. For nematodes on a sponge, rates are 1 million/ 1,000 sq. ft. 

Stratiolaelaps scimitus is a soil dwelling mite that is a favorite because, once applied, it can persist for the crop cycle, feeding on thrips, fungus gnats, pathogenic nematodes, weevils and overwintering pest mites. Some growers also release them around posts, plumbing or any cracks that allow them to find the overwintering spider mite populations. They will continue to reproduce as long as food is present. Keep this generalist predator in your greenhouse. Rates are 10-25/sq. ft. at time of planting. 

Dalotia coriaria is a native species of soil dwelling rove beetle. The species name coriaria refers to the beetle’s tough, leathery appearance.  Both adults and larvae are active predators and attracted to damp areas. They also control shore flies and will establish in pipes and drains where shore flies reproduce. The adults are highly mobile and can also fly up to the foliage and feed on thrips and spider mites. Rates are .1 - .5/ sq. ft. or 100/1,000 sq. ft. Nematodes, Strat mites and Dalotia work together well and can be used simultaneously.

Learning how to control greenhouse pests during separate stages of their life cycle and throughout the growing life of the plant will help with overall biocontrol success. It takes patience and planning when using BCA’s. Just remember, ‘At the end of the day you’re another day older’ and wiser.