Sparganothis Fruitworm
Sparganothis sulfureana
A leaf-rolling caterpillar that is a major pest of cranberry and also attacks blueberry. The larvae web leaves together and then bore into developing fruit, hollowing out the berries, and a summer generation does the worst fruit damage.
🔎 How to spot it
The adult is a small moth with yellow forewings crossed by magenta or orange scales that form a V on each wing, so the resting moth shows an X-shaped mark on its back. Young larvae are tiny with a black head and look like blackheaded fireworms, while older larvae have a dark to yellowish-brown head and a body that is darker green above and paler below, reaching about two thirds of an inch. The webbed-together leaves and uprights are a key sign.
🥀 Damage it causes
Larvae first web leaves and shoot tips together with silk and feed inside the shelter, then move to the fruit. They bore into developing berries and hollow them out, sometimes leaving clean feeding holes. Unlike cranberry fruitworm, which packs the berry with frass and turns the inside brown and mushy, Sparganothis larvae leave the fruit cleanly hollowed. The summer generation, which feeds on both foliage and fruit, causes the heaviest loss.
🛡️ Prevent it
Keep down weeds such as yellow loosestrife that serve as hosts, and monitor adult flights with pheromone traps so any treatment is well timed. Conserve natural enemies by avoiding broad-spectrum insecticides, since egg parasitoids and parasitic flies help hold the pest down. Remove and destroy heavily webbed growth where practical.
🧯 If it is already here
Time any control to the young larvae, which are the vulnerable stage; a single well-timed application after bloom, roughly two weeks after peak pheromone trap catch, is the usual recommendation, using reduced-risk products rather than broad-spectrum sprays that disrupt natural enemies. During bloom, only insect growth regulators and Bt-based products should be used to protect pollinators.
💡 Good to know
The pest has two generations a year and overwinters as an early-stage larva. The first-generation larvae feed mainly on foliage in spring, adults fly in late June and July, and the second-generation larvae are the ones that damage the fruit before going into overwintering by fall. It is a generalist that can use many wild and cultivated plants as hosts.
🌱 Plants it attacks
4 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.