Our community vegetable garden has been overrun with wireworms this year. Is there anything we can do to control them?
Here are the links I’ve located which mention some organic controls for wireworms:
Vancouver Sun article by Randy Shore on organic managmenet of wireworm and root maggot. Wireworm Biology and Nonchemical Management in Potatoes in the Pacific Northwest (specific to potato crops in the Pacific Northwest, but includes useful information that shows the science to back up suggestions in the previous link)
As you might expect, organic methods are not the toxic silver-bullet approach to pest management–they are longer range. You might have community gardeners plant their crops in containers for the time being (or maybe someone would be willing to donate raised beds?).
I consulted Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest by Linda Gilkeson (New Society Publishers, 2011). Here’s a summary of what she says:
- Check the soil for the eggs of adult beetles in April and May.
- “Wireworms can be especially damaging for the first few years after new sod is turned for a garden.”
- Larvae take 3-6 years to develop into adults. The worst damage is in spring and fall when they feed close to the soil surface. In summer and winter, they burrow deeper–but they also do this when there is nothing to eat. As you have already noticed, they are attracted to plant roots.
- Planting late avoids some wireworms. The author recommends not planting fall rye as a cover crop, as it attracts adults to lay eggs there. “Instead of cover crops, I prefer to keep empty garden beds weed-free all winter and use compost and leaf mold to add organic matter. Sow extra seeds of peas, beans and corn to allow for losses. Lightly fork over the soil in annual beds several times before planting and pick out wireworms; their light color makes them easy to see against the soil.”
- She suggests removing all weeds and roots from the bed. Then, use chunks of potato and carrot as bait, skewering each chunk on a short stick (to serve as a marker) and bury the pieces a few inches deep in the soil. Pull up the wireworm traps every day or two and destroy the worms. “For heavily infested soil. it might be worth trying ‘trap crops.’ Starting with bare soil, about 10 days before you want to plant the bed, sow rows of wheat or barley (about four seeds per inch) about a yard apart. The germinating seeds attract the wireworms if there are no other roots in the soil. After 10 days, pull the grain seedlings and destroy any wireworms found in the soil along the row and among the roots.”
- About parasitic (beneficial) nematodes, she says that the only species that has shown some effectiveness against wireworms is Heterorhabditis bacteriaphora.