Reply To: How do you treat armyworms in pasture grass?

[E. Vinje]

Hi Doris –

All of the natural pesticides that we recommend on our Armyworm Control page are short-lived in the environment and have less toxicity than commercial chemical sprays. With that said, I recommend using Bacillus thuringiensis (Bt-k) to treat armyworms in pastures. I feel it is the safest, most effective product that you can use for this application.

Harmless to humans, animals and beneficial insects, Bt-k is derived from a naturally occurring soil bacteria. It must be consumed by the caterpillar, as it is a stomach toxin. After ingesting the insecticide, ​caterpillars immediately stop feeding, though they may otherwise appear to be unaffected for several days.​ ​Bt-k degrades quickly in sunlight and ​should be applied ​at 5​-7​ day intervals while they are active. Apply more frequently to control heavy infestations.

Hope it helps!