Fall Armyworms active in Kansas

Fall armyworms are currently active in many areas of Kansas and many homeowners are wondering how to protect their lawns from the feeding damage that can occur during an outbreak of these hungry caterpillars .

Here are the basics to understand:

Fall Armyworm

Hosts: Fall armyworm feed primarily on grasses, although they will sometimes feed on various other non-grass species including some vegetables.

Identification: Young worms are ½- to ¾-inch long. Mature ones are 1 1/2 inches long. Body color may vary from green to almost black but light stripes will be visible along the length of the body. Look for a whitish inverted “Y” on the top of the dark- colored head.

Description: Fall armyworms are a tropical insect species. Only southern Florida and southern Texas have mild enough wintertime temperatures to allow their survival year round. Fall armyworm activities in non-overwintering areas such as Kansas begin when moths move northward after the winter and begin egg laying activities. Once established, additional generations can occur every 23-25 days. In Kansas, 2-4 generations of the moth/caterpillar can occur in one season depending on when they first arrive.

Fall Armyworm

Female fall armyworm moths have the ability to produce approximately 1000 eggs which they deposit in clusters containing up to 400 eggs each. Larvae produce a silken thread which allows them to drop or be blown to their food source.

Scout your lawn: In some years fall armyworms build up in large numbers. It is important to scout the lawn regularly for fall armyworm when an outbreak is known to be occurring. Look carefully for the larva in early morning or evening hours since they are more likely to be actively feeding when temperatures are cooler. Armyworms should be controlled when plant damage is becoming excessive or excessive numbers of caterpillars are found.

Damage: Smaller larvae will do superficial feeding, while larger larvae cause more extensive damage. Damaged turf grasses may become withered and brown. Under large populations, the appearance of “browned areas” occurs in very short order (24-hours or less). However, fall armyworms seldom kill grass. In most cases rather than eating a plant down to the crown/growing point, larvae will select a more tender adjacent grass blade to feed upon.

Under heavy feeding pressure, larvae may be forced to feed deeper down on a plant, but usually, when the food supply becomes scarce or “tough”, the larvae will move “in mass” to adjacent areas where there is a “fresh stand” of food to feed on. Thus, having moved on and given that they usually do not “eat plants into the ground”, a flush of new growth restores the appearance of the turf. Rain and/or irrigation will help to speed up the regrowth process.

Recommendations: If insecticide applications are considered, carbaryl (Sevin), cyhalothrin (Spectracide Triazicide), permethrin (38 Plus Turf, Termite & Ornamental Insect Spray; Lawn, Garden, Pet, & Livestock Insect Spray; Eight Yard & Garden RTS) and spinosad (Conserve, Monterey Garden Insect Spray, Captain Jack’s Dead Bug Brew, Natural Guard Spinosad) and Dylox (BioAdvanced 24-Hour Grub Control) are commonly available materials registered for control of fall armyworm in turf. Spray treatments will work more quickly than granular applications.

Granular treatments require irrigation or rain to activate the insecticide from the dry granular carrier. Professional lawn care service personnel have access to additional materials which may have more persistence than homeowner products.