What Mowed Down Your Seedlings?

What a shock! You get up in the morning to tour your vegetable garden, in perfect condition the day before, only to find some of the young plants mowed down, cut off at the base. What could have done it?

Cutworm

The answer is the “cutworm,” the larva of certain moths called noctuids, belonging to the large family Noctuidae (e.g., Agrotis ipsilon, Feltia subterranea, Euxoa spp., etc.). The moth lays its eggs in the soil in the fall or early spring, often in weeds or grasses near the garden. Some larvae spend the winter in the soil, ready to attack as soon as the soil warms up.

The grub is often grayish in color and curls into a C shape when disturbed, a typical behavior of these larvae.

Cutworms can cause considerable damage to young plants, especially vegetables, but also annuals, perennials, and other seedlings. Upon hatching, usually in late spring, the larvae emerge from the soil at night and gnaw at the base of the plant, causing it to collapse to the ground. Some species may even gnaw slightly below the soil surface.

Hand-picked

To stop the disaster, you’ll have to do a bit of prospecting. With a flashlight, go out into the garden the next night and look for the culprit (it starts to move to the surface of the soil at dusk): cutworms never go very far and should be in the same area where the plants were cut down the day before. Or, if you prefer working in daylight, dig around in the soil near the fallen plant with a trowel, about 2 inches (5 cm) deep: a cutworm is not hard to find.

Fortunately, cutworms aren’t alone in your garden: an army of natural allies can help you control them. Several insectivorous birds love the larvae they find by scratching the ground. At night, ground beetles patrol the base of plants to catch cutworms in action. Other beneficial insects such as earwigs, rove beetles, and lacewing larvae also contribute. Even toads, small snakes, and bats play their part: the latter feed on adult moths before they have time to lay their eggs. To support these valuable predators, it is a good idea to diversify the plants in your garden, provide hiding places (stones, mulch, hedges), and avoid broad-spectrum pesticides that decimate them.

Prevention

Or be proactive and protect the base of your plants and your transplanted seedlings before cutworms attack. Cut the bottom off a few cans, plastic pots or plastic, styrofoam or cardboard cups, thus forming a tube. You can even use the tube from a roll of toilet paper! Place a tube barrier around each seedling, pressing the lower part of the barrier into the soil to a depth of 1 inch (2 cm). With a barrier around the base of the plants’  stem, cutworms, which always act right at soil level, will find nothing to eat and will either die or move elsewhere.

This text was first published on this blog on May 22, 2015. It has been revised and its layout has been adapted.