Cranberry Fruitworm on Blueberries

This pest overwinters as a fully grown larva in litter near the soil surface under the bushes. The small, brown, adult moths emerge in spring around the time of bloom, mate, and the female begins laying eggs within the calyx cup as berries are just beginning to form. The larva enters the berry soon after hatching. It eventually webs several berries together with silk, feeding inside as many as six. There is one generation per year. The cranberry fruitworm infestation is characterized by masses of brown frass (excrement) and silk.

Cranberry fruitworm infestations can be difficult to detect early. Look for a pin-sized entry hole near the stem of any small, shrunken berries that have turned blue, and then open adjacent berries to find the larva. Eggs may be detectable as well, changing in color from white-green to yellow.  The distinctive frass and webbing do not appear until later in the larva's lifetime when it begins to move between berries. One method of control for this pest (and for cherry fruitworm) is to pick and destroy infested berry clusters showing evidence of webbing. Repeated disking to eliminate weeds and trash also helps in its control.