Bryan Smith, Area Extension Agent-Agricultural Engineer
This fall a huge number of Fall Armyworms invaded Laurens County. Fall Armyworms are usually in our county in some small number each year, but this year’s numbers created quite a bit of damage in landscapes, pastures, and hayfields.
Fall Armyworms migrate northward each year from the Gulf coast and may arrive in Laurens County as early as August. There may be as many as three “waves” of armyworms each year depending on many factors. The Fall Armyworm life cycle is typically 30 days in the summer, with the larval or caterpillar stage being the destructive one. Fall Armyworms remain in the caterpillar stage for 14 days and are most destructive during the last 4 days of that stage. They then pupate and emerge as moths, which feed on nectar from various flowers and are not destructive.
Fall Armyworms seem to prefer bermudagrass, crabgrass, johnsongrass, millet, and sorghums. They will ignore other grasses such as fescue and bahia while sufficient quantities of their preferred foods are present. However, if those food sources are exhausted before they pupate they will move to less desirable species and decimate them as well. This happened in 1977 in Laurens County when Fall Armyworms killed entire pastures of fescue after they had eaten their preferred crops.
Rainfall does encourage the growth of fungi that are detrimental to Fall Armyworms, but it does not kill them. Clemson Extension recommends that insecticides be used to control them when growers see 3 armyworms in a one square foot area. If Fall Armyworms are found in a hay crop we recommend that the hay be harvested if it has enough growth to do so – Fall Armyworms eat green growth and will not eat cured hay. Local Extension Offices can provide a list of insecticides labelled for use in lawns, pastures, or hay fields.
