The Shutter Diagnostic Lab received a picture of a moth in the Crambidae family, also commonly called snout moths, grass moths and sod webworms, from Blaine County. While driving to Rock Springs (north of Miles City) on September 3, these moths were very abundant throughout much of the Eastern Region of Montana. Many of these moths likely originated from surrounding pasture and rangeland, and become more obvious when they congregate on the sides of buildings.
The adult moths do not damage crops or lawns and do not require treatment.
The juvenile caterpillar stage (webworm) spins webbing near the surface of the ground where it
lives. At night the webworm larvae feed on grasses, chewing off leaves and stems just above the
crown. Some species are pests of lawn and turf because their feeding produces brown patches.
The moths that are flying now will mate and begin laying eggs in grassy areas. The small
juvenile caterpillars will hatch this fall and overwinter in silk tunnels they construct. Next spring
the webworms will resume feeding.
In rangeland and pasture densities of this pest are not usually high enough to warrant treatment. However, this pest may cause damage to lawn and turf grass in urban areas. Brown patches in lawn and turf that appear during the spring of 2016 can be surveyed for the damaging webworm larval stage, and if present, treatments can be applied if the damage is severe.
The juvenile caterpillar stage of grass (snout) moths feed on grasses
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Source: MSU Ag Alerts
