The armyworm is native to North America and got their name by their army-like fashion of moving across fields. As the larvae consume the food available to them, they move as a whole group to a new food source, eating as they go. The weather can greatly affect armyworms; a wet and cool spring will favor their development but will hinder predator and parasite population.
Reproduction and Life Cycle
There are some varieties of armyworms that overwinter and others that migrate. Female armyworms deposit eggs in cluster or rows on the lower leaves of grass and the base of plants. Eggs take about 1 to 2 weeks to hatch after being laid. After the larvae goes through 6 instar or molting stages, the larvae will pupate below the soil line and emerge as adult moths 1 to 2 weeks later. There is typically a second generation and third generation occurring from June until September, that being said, some varieties of armyworm can lie up to 6 times.
Armyworm Identification, Varieties and Habitat
Armyworm larvae can come in a variation of colours from dark brownish-green to black. On either side of their abdomen they have long pale orange, white and dark brown stripes. The head capsule of the armyworm larvae is yellow-brown with brown veins. On the outer side of each proleg, armyworms larvae have dark bands. A fully mature larvae is about 1 ½ inches long. During the pupa stage of the armyworms life they stay in a brown shell sitting just below the soil surface. Once the larvae are done pupating, they emerge as moths that have a wingspan of about 1 ½ inches with light brown to tan wings that have a tiny white dot in the center of each forewing. The eggs that the female armyworm moths produce are small, round and white. Once the female is done laying one mass of eggs, she will roll the leaf blades they are on around the mass.
- - Fall armyworm (Spodoptera frugiperda)
- - Beet armyworm (Spodoptera exigua)
- - Western yellowstriped armyworm (Spodoptera praefica)
- - Yellowstriped armyworm (Spodoptera ornithogalli)
- - Bertha Armyworm (Mamestra configurata)
Throughout the day, armyworm moths typically remain hidden in grassy area and are active during the evenings eating nectar, mating and finding an appropriate area to lay their eggs. Newly hatched larvae are also active during the night and feed on host plants. For the duration of the day armyworm larvae live under plant debris or in the top of the soil. Although the primary plant to be eaten by armyworms is grass such as barley, corn, fall rye, forage grasses, oats, and wheat, they sometimes will feed on vegetables including, carrots, onions, radishes, sweet potatoes, cabbage, peas, peppers, and beans.
Armyworm Management and Control Methods
Economic infestation does not typically happen on an annual basis. To develop economically damaging numbers of armyworms is dependent on spring moth flights, weather conditions, cropping practices and natural enemies. For most years, the population for armyworms is kept below damaging levels by the factors listed above. Start looking for signs of damage and larvae in early spring.
There are naturally occurring predators such as birds, lacewing, ladybugs, wasps, certain flies, rove beetles and ground beetles that are important for keeping the population of armyworms low each year. If you till your soil in the fall it will expose the pupae armyworms giving the birds a chance to pick them off. The risk of armyworm infestation can also be minimized by eliminating or controlling grassy weeds that are in and around fields. Handpicking the worms is also an option; once picked, the best disposal is putting them in a bucket of soapy water.
It is important that you do your best to avoid using harmful pesticides or practices that could injure beneficial insects, which should be your first line of control on armyworms. That being said, natural horticultural oil spray can be used on plants that are showing signs of infestation. Multi-purpose neem oil spray can be an effective control method of larvae. It is critical that there is complete coverage, including the junction with stems and the bottom side of the leaves. If you are looking to take chemical control, it is best applied to apply insecticides as soon as the economical threshold has been reached. One well-timed application of a registered insecticide with high clearance spraying equipment is typically best. Products that work well depending on your crop is Decis applied at 40-60 ml/per acre, Lorsban at 305-405 ml/acre, Lannate at 360-500 ml/acre, Monitor at 230-500 ml/acre and more, can provide adequate control. For the best control of armyworms, apply insecticides early in the morning or late evening when the larvae are active. Be sure to carefully read the label for cautions and proper application. It is extremely important to never spray on days that are windy or when temperatures are higher than 25˚C.