Nematodes in Spring
Prevent plant damage with beneficial nematodes.
Beneficial nematodes provide one of the most effective and easy-to-use biological controls for certain difficult insect pests. Beneficial nematodes only attack insects with a soil-dwelling development stage, so they pose no risks to other animals nor to most other beneficial insects and pollinators. Because they are sensitive to sunlight, drought, and also restricted by cold soil temperatures, in western Oregon nematodes are mostly applied in the fall or the spring, on moist soil and during the cool hours of morning or evening.
Wait for soil to warm a bit for best results, as early as April or as late as mid June. Where pest problems are extensive, try a second application about 2 weeks after the first.
To use beneficial nematodes, first get a rough measurement of how large of an area you need to treat. The common small size package of 10 million nematodes (no, I didn’t count them!) can treat an urban garden, a dozen or more mature shrubs, or a small front yard – maybe 2000 square feet. If you are trying to stretch them as far as possible, apply through a sprayer – but if you are treating a few raised beds or rhododendrons it will be easier to use a watering can.
With that in mind, create a solution of nematodes by soaking the media they come on in a bucket with a gallon or so of water. Skim the media off the top and scatter it into the treatment area; for a small area add enough solution to half fill your watering can and top it off with more water, then pour as evenly as possible over the treatment area. For larger areas, pour the solution through a filter into your sprayer. A gallon run through a sprayer should cover about 750 square feet, so if you are doing an entire 2000 square foot yard, mix one part of your solution with two parts water to make enough volume for coverage.
See package or ask your local nursery for additional application suggestions or advice. A light watering after application is recommended (if the rain doesn’t do the job for you).