Armyworms Can Be A Real Problem In Garden

This armyworm had plenty to choose from in a well-stocked vegetable garden.

 

By Les Harrison
Wakulla County Extension Director

Guests which are picky eaters are no fun, especially for a host. No matter what dish is served, there is always something wrong with it.

It can be the wrong flavor, incorrect seasoning, improperly prepared or some other culinary offense which repels the persnickety visitor, and frustrates the gracious and long suffering person who is making all attempts to satisfy the invitee.

Among Wakulla County’s many butterflies and moths, there are plenty of finicky caterpillars which will consume only one or a very limited list of plants. Depending on the situation, these larval-state can be a minor annoyance or a manageable problem.

It is the easy-to-please which can be a real problem, particularly when they invite the entire extended family and friends to join them. Chief among these is the southern armyworm.

This insect is native to the warmer regions of both American continents. It occurs widely in Central and South America and the Caribbean. In the United States, the southern armyworm is found principally in the southeastern states with its range extending as far west as parts of New Mexico.

The number of generations has been estimated at four annually in Florida. About 30 to 40 days on average is required for a complete generation, with environmental factors restraining even more reproduction.

In northern Florida moths which produce this caterpillar can be found throughout the year and have the capacity to withstand several days of freezing weather. Eggs are laid in clusters, and covered with scales from the body of the moth.

Duration of the egg stage is four to six days and they are placed on or very near potential food.  When they hatch, the problems for gardeners and homeowners begin.

The larvae undergo six instars or development phases as they grow to attain a terminal length of about an inch and a half. In this stage of life they are defoliators and feed aggressively for the first few weeks, often skeletonizing leaves with only the main stems remaining.

Initially they remain in groups, but as they mature they become more solitary. As they grow they will bore readily into fruit, often damaging it and rendering it unusable. When stressed by a lack of food they will eat the portions of branches, bore into stem tissue, and attack tubers near the surface of the soil.

Larvae usually are found on the lower surface of leaves, and well hidden from birds and other potential predators. With no defensive ability except hiding in the foliage, they are most active at night.

The length of the larval stage is normally 14 to 20 days, but weather conditions and temperature can influence the timing. All this time they are eating, and the menu offerings in Wakulla County is substantial.

This species will consume vegetable, fruit, field and ornamental crops, including beets, cabbage, carrots, collards, cowpeas, eggplants, okra, peppers, potatoes, sweet potatoes, tomatoes, and watermelons.

Other crops include citrus, peanut, sunflower, and various other ornamental flowers. Turfgrass and forage crops are rarely eaten by this species of armyworm, but other species will readily consume them.

Many weeds are munched by this pest, but pigweed (Amaranthus spp) and pokeweed (Phytolacca americana) are especially favored. Sometimes these weeds are the deposit point for the female moth’s eggs and the larvae move to the home garden or landscape as they grow.

This caterpillar is best controlled with foliar insecticides when larvae are small, but there are natural enemies too. Several wasps parasitoids utilize this species to feed its young.

Still, a frustrated gardener waiting for peppers to ripen can be revengeful when they contain a fat and, at least for the moment, happy armyworm.

For more information on armyworms in Wakulla County, contact the UF/IFAS Wakulla County Extension Office at 850-926-3931 or http://blogs.ifas.ufl.edu/wakullaco/.