Cherry Fruitworm (Grapholitha packardi)
Cranberry Fruitworm (Acrobasis vaccinii)
Insects & Invertebrates
Symptoms
Larvae of both species feed on the inside of fruit by creating a pinhole entrance. One larva is able to destroy several berries by moving between and feeding on berries in a cluster. Symptoms are seen as prematurely blue, shrunken berries since the penetration holes are often not seen. Small entrance holes may appear as brown trails caused by tunneling. Cranberry fruitworm feeding can be identified as frass inside the fruit and the berry cluster clinging together with silk webbing. Larvae may eat only part of the berry or completely consume the inner flesh of a berry.
Identification
Adults of both species are small, dark gray moths with a wingspan of about 1/3 inch (9 to 10 mm). Cranberry fruitworm moths have white patches on their wings. Larvae are smooth caterpillars that will grow to 3/8-inch (9 mm) in length. Cherry fruitworm larvae have pink-red bodies with brown or black heads. Cranberry fruitworm have green bodies with dark heads.
Life History
Fruitworms overwinter as large larvae in cavities usually made in the dead wood on the bush. The adult moths emerge in the late spring. Green-white flattened eggs are laid on the underside of leaves as well as on developing small green fruit. After hatching, larvae enter the berries. They usually feed on one berry and then penetrate and feed on another. Cherry fruitworms seal entrance holes with silk so that frass is not visible outside the berries. Both species have one generation per year.
This Lepidopterous pest is found on a number of host trees including cherry, apple, rose and hawthorne, all of which are commonly found near blueberry fields.
Monitoring
Fruitworm infestations may be difficult to detect early in the season because there is little external evidence of the insect's presence. 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. Evidence of Cranberry fruitworm can be seen as frass in the fruit and clusters clinging together with webbing. Pheromone traps are available for Cranberry fruitworm, but this will not attract the Cherry fruitworm.
Management
Remove overwintering environments for larvae, such as weeds and trash around plants; also manage alternate hosts on borders. In small plantings or with low infestation levels, fruitworm can be controlled by hand removing infected fruit. When damage is severe, treat with insecticide. These should be used when larvae are small, usually starting at petal fall.
Web Resources
Michigan State University; Fruitworm Identification in Blueberries
http://web1.msue.msu.edu/fruit/bbfrtwm.pdf
Michigan State University; Blueberry Facts; Cherry Fruitworm
http://www.blueberries.msu.edu/chryfrtwrm.htm
Michigan State University Extension; Fruit IPM Factsheet; Cherry Fruitworm
http://web1.msue.msu.edu/vanburen/cherry_fruitworm.htm
Michigan State University; Blueberry Facts; Cranberry Fruitworm
http://www.blueberries.msu.edu/crnbryfrtwrm.htm
Michigan State University Extension; Fruit IPM Factsheet; Cranberry Fruitworm
http://web1.msue.msu.edu/vanburen/fcranfrw.htm
Ontario Ministry of Food, Agriculture, and Rural Affairs; Control of Cranberry and Cherry Fruitworm in Highbush Blueberries
http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2005/08hrt05a5.htm
North Carolina State University; Cherry Fruitworm
http://ipm.ncsu.edu/small_fruit/cherworm.html
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