I was keeping my fingers crossed that I would never see fall armyworms feeding on our lawns again. No such luck! They are back so be on the lookout for these critters! Fall Armyworm primarily feeds on grasses, although they will sometimes feed on nongrass species.
Damage
Although armyworms may be better known as agricultural crops pests, they can be a sporadic but serious pest of turfgrasses. Fall armyworm damage in turfgrass is very distinctive. Since armyworms cross the turf surface as a group, they create a noticeable line between damaged and undamaged turfgrass. Usually damaged areas will originate around a site where egg masses can be easily laid (signposts, buildings) and radiate outward. Although fall armyworms do not have many specific preferences, newly-installed sod is more attractive and more susceptible to damage.
Biological Control
Often, natural enemies can keep fall armyworm populations in check (ie: lady beetle). However, cold, wet springs can reduce the effectiveness of parasitic organisms and cannot effectively control large armyworm populations.
Chemical Control
Fall armyworms can be more difficult to control than other caterpillar pests (true armyworms, black cutworms). When possible, mow and lightly irrigate the turf prior to treating. Insecticides are generally ineffective against large larvae so be sure to note the size of the armyworms before making an application. Large larvae are likely to finish feeding and burrow into the soil to pupate so only treat if larvae are relatively small. Pyrethroids (particularly lambda-cyhalothrin) and carbamates (carbaryl), will provide somewhat effective control against smaller larvae.
Cyhalothrin (Spectracide Triazicide), permethrin (38 Plus Turf, Termite & Ornamental Insect Spray; Hi-Yield Garden & Farm Insect Control; 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 have greater and quicker contact efficacy 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 (such as Scimitar and Deltamethrin) which may have more persistence than homeowner products.
