Eliminate Cutworms Using Natural Pest Control

Excerpt from a field guide to natural pest control eliminating cutworms from crops, including using the cutworms predator, the tachinid fly, caterpillar-killing bacterium, insect-killing nematodes, and more.
By Susan Glaese
March/April 1987
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The cutworm (inset) is probably the most common and troublesome early spring pest facing North American gardeners. The tachinid fly (right preys upon these pests, which can also be controlled by paper-collaring seedlings.)

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The second issue of American Country, MOTHER's new sister magazine, contains an indispensable field guide to natural pest control. This brief excerpt will help you keep cutworms from your crops.

Eliminate Cutworms Using Natural Pest Control

Cutworm (Noctuidae family)

Range: Throughout North America
Description: 1 inch grayish brown caterpillars, some with spots or stripes. Nocturnal-rarely seen in daytime. Curl up when disturbed. Adult "Miller's moth" is gray or brown with paler hind wings and 1 inch to 1-1/2 inch wingspan.

The name cutworm is justifiably ominous. You won't know you've got cutworms in your garden until they've performed their guillotine act and decapitated several of your plants. There are approximately 20,000 kinds of cutworms, including tunneling, subterranean, and climbing species (such as the armyworm), but the surface feeders are the most common. These spend two summers as destructive larvae (overwintering in the soil) before they mature into harmless moths.

Modus operandi: Fells young plants by cutting off stems at or just below soil surface. Favorite victims: Your carefully nurtured garden seedlings.

Natural Pest Control Methods for Cutworms: 

• The traditional-and very effective natural pest control method is to set a small 2 inch to 3 inch collar, pressed 1 inch into the soil, around each vulnerable plant. Collars can be made of paper, cardboard, PVC, metal cans, paper cups, or toilet tissue tubes.
Bacillus thuringiensis, a widely available caterpillar-killing bacterium,is a very effective control for climbing cutworms as well as for the surface feeders.
• Handpick larvae at night by flashlight.
• Mulch plants with oak leaves, crushed eggshells, damp wood ashes, or other skin irritating physical barriers.
• Deep plowing, digging, or tilling in fall and again in spring will expose and kill soillaid eggs and overwintering larvae. Chickens let into the plot after these cultivations will help improve the effectiveness of this technique.
• Tachinid flies, trichogramma wasps, braconid wasps, and insect-killing nematodes parasitize cutworms.
• Toads, moles, shrews, blackbirds, meadowlarks, and firefly larvae are all natural predators.
• The adult moths can be attracted to, and killed by, electronic bug zappers.
• Sprinkle cornmeal around your garden. Cutworms love it but can't digest it. Some will die from overeating the treat.
• Make a mixture of molasses (another vice), water, wheat bran, and hardwood sawdust. Circle plants with this glop. It dries on the cutworms' bodies and immobilizes them.
• It's said that if you push a small twig, nail, or toothpick into the earth right next to a seedling, the cutworm cannot wrap around the stem and fell the plant.
• According to University of British Columbia student Greg Salloum, cutworms would rather starve than eat plants treated with extracts of pineapple weed or sagebrush.

Tachinid Fly (Tachinidae family)

Range: Throughout North America
Description: Looks like a common housefly, about the same size (1/8 inch to 1/2 inch) and color (gray-brown). There is one significant distinction: Houseflies don't have the prominent abdominal bristles that tachinids do. But these are hard to spot on a fly in flight, and tachinids are very active and quick fliers.

Modus operandi: Adult tachinids are fond of nectar and insect honeydew and are therefore often found on flowers or foliage. It's the tiny yellow larvae that prey on garden pests. These maggots eat the flesh of cutworms, sawflies, Japanese beetles, Mexican bean beetles, gypsy moths, grasshoppers, corn borers, and many caterpillars.

Tachinid larvae feed mostly on muscle tissue and fat, allowing their host to remain alive, though sickly, for a good while. Sometimes a host caterpillar will even live long enough to spin a cocoon or chrysalis before it dies. No moth or butterfly emerges from that tomb, though-just more tachinid flies!

A tachinid larva also has a remarkable way of assuring its respiration. It either attaches its rear end, which contains its respiratory organs, to the victim's tracheal system, of makes sure its bottom pokes out from the prey's body.

A tachinid mother means business. She has three ways of assuring meal tickets for her offspring. First, she may glue her eggs to the victim's skin, being careful to place them out of reach-right behind the victim's head. Second, she may lay them on foliage near host insects. The larvae will then hatch near their prey or even be ingested by the unwitting victim. Third, some tachinids (there are over 1,300 species) can hatch the young within their own bodies and then attach the larvae to a host. This tactic can backfire, though. If the mother doesn't find a good host, her offspring may devour her.

Sources: Tachinid flies are native to most areas of the U.S., so try not to spray your garden with any all-purpose pesticides. And never swat a fly in your vegetable plot unless you know for sure what it is.

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