Cranberry Blossomworm is one of the most important pests of cranberries in New Jersey; however, it is considered a minor problem in Massachusetts, Quebec, and British Columbia, and not known to infest cranberries in other growing states.
The cranberry blossom worm has one generation a year. Eggs are laid singly mostly in October on fallen leaves and pieces of dead vines littering the bog floor. These eggs overwinter and begin to hatch from late April to early May. Young larvae are green but older larvae become reddish brown with a whitish stripe along each side of the body. Mature larvae become pale brown and nearly 38 mm long (see picture 1). Larvae become nocturnal by mid to late May.
Pupation takes place in the ground or deep trash in late July and early August. The moths (Picture 2) start to emerge in September and are active until late November.
Young larvae nibble the leaves or bore into the buds. Fruit production is further decreased as older larvae nip off buds and blossoms, dropping them to the ground often cutting off more blossoms than they can consume. Each mature worm can fully destroy 100 blossoms over a three-week period.
Monitoring for this pest requires nighttime (9 pm to 12 am) sweep net sampling. If numbers exceed the threshold of an average of 4.5 larvae in sets of 25 sweeps, we recommend insecticide sprays. We recommend the use of the insect growth regulator (IGR) Intrepid if populations exceed action thresholds. Intrepid is reduced-risk, softer insecticide that is very effective against lepidopteran pests.