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Jessica Walliser

Managing corn earworm is easy with these tips

Jessica Walliser
| Saturday, Sept. 1, 2018, 11:03 p.m.
Plant flowers like sunflowers and zinnias in and around your sweet corn patch to help limit damage from corn earworms.
Plant flowers like sunflowers and zinnias in and around your sweet corn patch to help limit damage from corn earworms.

Sweet corn is one of summer’s most cherished crops for gardeners. There’s nothing like walking into your own backyard, pulling a few ears off the stalk and enjoying them just minutes after harvest. But, if you grow your own sweet corn, or even if you buy it from a local farmer’s market, you’ve likely come across Public Enemy No. 1 in the corn patch: the corn earworm.

Corn earworms are extremely challenging pests to manage, especially for organic farmers and gardeners. The trick to ridding your corn patch of these kernel-munching caterpillars is multifaceted.

First, it’s important to understand how this pest lives and feeds in the garden. Corn earworms (Heliothis zea) are the caterpillars of a small nocturnal moth that’s drab brown and olive green. The caterpillars are most often found just below the silks at the tip of the cobs, feeding on the kernels inside. They can grow up to an inch long and have a black or creamy yellow stripe down the side of their body.

You might be surprised to learn that corn earworms also feed on tomatoes where they create perfectly round holes in ripe or near-ripe fruits. When feeding on tomatoes, they’re known as tomato fruit worms.

In the corn patch, however, is where they cause the biggest problems. Female moths lay eggs on the silks of the developing ears early in the season. The young caterpillars migrate down the silks and into the ear, feeding on the milky kernels. It’s tough to miss these caterpillars when you peel open the husk of a newly harvested ear and discover they’ve eaten the tip of the cob and left a brown mushy mess.

The good news is that corn earworm damage can easily be cut from the cob. Simply use a sharp knife to cut away the damaged tip of the corn and enjoy the rest of the cob as usual.

But, if you want to control this pest in your home corn patch without having to turn to harsh synthetic pesticides, there are a few tricks you can employ. Pinning the tops of the ears closed soon after the silk begins to develop will keep the young caterpillars from crawling into the cob. Clothes pins are great for this job. You can also wrap the top of the husk closed with a piece of clear packaging tape. Though this method isn’t 100 percent effective, it does work quite well.

Another option is to apply five drops of corn oil mixed with a biological insecticide called Bacillus thuringiensis (Bt) that targets only caterpillars. Mix 3 tablespoons of Bt with a quart of corn oil then use a dropper, turkey baster or even a squirt gun to apply the product to the tip of each ear. Yes, it’s time-consuming, but you only have to do it once to see great results. It’s a technique that would be very challenging to do on a large commercial farm, but in a home corn patch, it’s much more manageable.

Lastly, be sure to encourage plenty of the beneficial insects that prey upon corn earworms to take up residence in your garden. A study showed that 70 percent of pest predation in a corn field takes place by spiders at night. Hunting spiders relish corn earworms as do many species of predatory beetles and other beneficial. Encourage these good bugs by planting a margin of flowering herbs and annuals around your corn patch. Sunflowers, cosmos, sweet alyssum, dill, fennel and daisies are great choices.

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,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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