To prevent potato damage, rotate crops and till up wireworms in fall
Question: My wife and I dug up our potato crop a few weeks ago and found that most of the potatoes were filled with small holes. When we peeled them for Thanksgiving dinner, we discovered the holes weren't very deep, and as long as we made the peels a little thicker, the inside of the potatoes were fine. What caused this, and is there anything we should do to keep it from happening again next year?
Answer: The small, shallow holes you discovered in your spuds are classic signs of wireworms. These slender, thick-skinned insects are the soil-dwelling larvae of several different species of click beetles. Though the adults don't damage plants, the larval wireworms do. They attack root crops like potatoes and carrots, as well as the roots of other crops, such as corn and melons.
Wireworms are tan to reddish brown, thin, and they have a shiny, hard shell. Their bodies are segmented, but they only have three pairs of legs just behind their head. Most species are between a half inch and an inch and a half in length. They can live from three to five years.
Wireworms feed on potatoes by tunneling through the surface. Sometimes they leave shallow holes behind, and other times they carve out some of the potato's flesh. Many times their feeding damage also leads to rot.
Because wireworms spend the winter in the soil as larvae, tilling your garden in the fall exposes them to predators and freezing temperatures. Crop rotation also is very important. Try to avoid planting potatoes in the same area for three or more years.
Some varieties of potatoes are more susceptible than others. In my garden, I've planted ‘All Blue' potatoes right next to ‘Cranberry' potatoes, and at harvest time, every ‘All Blue' tuber was riddled with wireworm holes, while not a single ‘Cranberry' potato showed signs of damage. Potato varieties said to be more resistant to wireworms include ‘Yukon Gold,' ‘Mountain Rose' and ‘Ozette.'
Wireworm damage is more extensive in the late summer and fall, so harvesting your potatoes in the “new” stage means damage-free spuds. New potatoes are those harvested from still-green plants earlier in the season. Their skins won't be cured, though, so new potatoes are meant only for fresh eating and not for long-term storage.
Beneficial nematodes ( Steinernema feltiae) applied to the soil also have been shown to effectively combat wireworm infestations. These can be purchased from Arbico Organics (arbico-organics.com) and Planet Natural (planetnatural.com). They're mixed with water and then poured onto the garden in the spring wherever potatoes will be planted.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com.
Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., Third Floor, Pittsburgh, PA 15212.
