To start with … what are nematodes?
Nematodes are very tiny, microscopic ‘worms’ that mostly live in the soil. Beneficial nematodes can range from 1/25 inch to several inches long and have slender, translucent, unsegmented bodies. Many are soil dwellers that break down organic matter, especially in compost piles. You can easily spot these 1/4-inch-long decomposers.
Beneficial nematodes are much more popular these days for soil pest control because they feed on over 200 pests from up to 100 insect families. Specifically they combat a variety of pest species, including weevils, clearwing borers, cutworms, sod webworms, chinch bugs, and white grubs.
When applied, the tiny juvenile stage of the nematodes seeks out their specific prey. One type (Steinernema) uses an ambush strategy, waiting for the prey to come close before attacking. Another nematode (Heterorhabdtis) uses a “cruising” strategy, seeking out and destroying pests. They either follow the trail of excrement of the pest, or search for it through changes in temperature and carbon dioxide levels.
Once found, the beneficial nematodes enter the grub or other pest through body openings, like the mouth or openings to the breathing tubes (“spiracles”). These juveniles carry a bacterium (safe for plants and the environment) that they release into the pest blood. These bacteria multiply, killing the pest in a couple of days or sometimes sooner, and convert the host tissue into food.
The grubs change from a beige-white to reddish brown when infected, die and turn slimy, and are soon hard to even find. The nematodes feed on the dead pest from within (hence they are called “entomopathogenic”), and can go through several generations of adults in a couple weeks. Once their food source is gone they exit and move on to new prey.
Pretty picture … right!
Being natural, the application of beneficial nematodes are safe to use around children and pets. They’re also safe for soils and won’t harm non-targeted organisms like bees or pollinators. Application is easy (no protective gear is needed), quick to work (often within a couple days), and cost effective. While you may need 20,000 or so to treat a square foot, they are so small that with a minimal investment, you can get about 5 million—enough to treat 1,500 square feet.
There are two periods when grubs can be targeted by nematodes, in the spring when soil temperatures are above 10°C (often early May to early June) and again in the fall before soil gets too cold (mid-late September to mid October). During those times the insects are in a life cycle where grubs are in the soil and can be targeted. The best time is in the fall when the grubs are smaller but the most common time is in the spring. Best practice is applying during both to get the ultimate coverage and protection!
Remember that the nematodes are living organisms, so should be applied very soon after you get them. They like moisture, so if it hasn’t rained, water thoroughly both before and after application. You can apply during the rain too. Since they come on a wet sponge, rinse them from this into cool water. Then use this as a concentrate to water or spray as per directions (see video). Then keep the soil moist for a week to 10 days after, if it doesn’t rain.
Rainy, overcast weather is good for another reason … nematodes are quite sensitive to the UV in sunlight, and can be killed within a minute or two if exposed to it. So we recommend application in early morning or late afternoon. They’re sensitive to temperature too, with ideal temperatures for our Canadian grown nematodes above 10C.
For prevention, you can apply 2 to 3 times a year, in spring, summer, and fall. For control of existing pests, apply every 2 weeks until the infestation lessens or goes away.
If you have any other questions or concerns about your pest and if beneficial nematodes are the answer … Ask Stacy.