Control Armyworm Pests in the Organic Garden

Armyworms damage many plants in the organic garden, including lawn grass and vegetable plants. Kill these caterpillar pests without chemicals.

The name armyworm conjures images of hordes of invaders marching through the lawn and garden, munching indiscriminately on the cultivated members of the landscape. Indeed, armyworms aren’t picky eaters, and they can inflict a great deal of damage in a short time. However, organic gardeners can control these garden caterpillar pests without resorting to toxic chemicals.

Identify Armyworm Caterpillars
It can be difficult to attribute garden damage to armyworms, because the worms are nocturnal and nondescript. Although the worms are about an inch long and as plump as a pencil, their greenish brown coloring helps them blend in with their surroundings. During the day, armyworms seek shelter under garden debris, so the gardener isn’t likely to observe the pests crawling around.

source

If large areas of the garden are damaged and caterpillar droppings are present, the gardener should use a flashlight to inspect the garden at night. Gardeners can distinguish the armyworm from the nocturnal cutworm by observing the damage: cutworms usually feed at the soil level, severing stems of young plants. Adult armyworm moths are brownish-gray.

Mechanical Control of Armyworm Pests
Organic gardeners can control armyworms without applying any sprays or powders to sensitive plants by using row covers on the vegetable garden, and by handpicking armyworms on small lawn areas at night. Gardeners must apply row covers early in the growing season to prevent the moths from laying eggs on vegetable plants. Remove the row covers from plants that require insect pollination, like cucumbers, melons, and squash, after flowers appear.

Organic Garden Spray for Armyworms
Neem is an effective organic spray for armyworm pests. Neem oil is a broad-spectrum pesticide derived from the oil of the neem tree, and it interferes with all aspects of the life cycle of the armyworm, including feeding and laying eggs. Gardeners shouldn’t apply neem to flowering plants to prevent damage to honeybees.

Biological Controls for Armyworms
BTK, or bacillus thuringiensis var. kurstaki, is a bacteria that produces a toxin specific to caterpillar pests like armyworms. The toxin paralyzes the digestive tract of the armyworm, but the caterpillar must first consume the BTK for it to be effective. In general, the bacillus products are heat and light sensitive, so the gardener should reapply the product frequently and buy fresh BT each year.

Beneficial Insects Kill Armyworms
Parasitic wasps feed on armyworms, so gardeners should attract these predators with nectar-rich plantings such as yarrow or sweet alyssum. Ladybugs and lacewing insects also feed on armyworm eggs and young larvae. Organic gardeners can buy green lacewing larvae and ladybugs from garden suppliers like The Beneficial Insect Co., Arbico Organics, or Planet Natural.