Identification, Biology and Management of Fruitworms in Utah Cherries, 2001

Diane G. Alston

Department of Biology, Utah State University

Objectives: To identify and learn more about the major species of fruitworms (Family Noctuidae) attacking tart cherries in northern Utah.

Methods: Two tart cherry orchards in Utah Co. were monitored for the presence of green fruitworm larvae in spring and early summer of 2001. The orchards were located in Payson and Genola. Two visits were made to the orchards in each April, May and June. Larvae and injury were photographed and collected. The specimens were identified. In 2000, several fruitworm specimens were collected by Michael Reding and identified.

Results: Two species of green fruitworms were collected in Utah Co. orchards: the speckled green fruitworm (Orthosia hibisci) and the pyramidal fruitworm (Amphipyra pyramidoides). Both species are in the Family Noctuidae. This family contains fruitworms, cutworms, armyworms, and earworms. The speckled green fruitworm has both a green and a brown or dark form. Both green and brown forms were found.

In 2001 surveys, the first detection of larvae in both orchards occurred on 17 May. Before this survey date, fruitworms and injury were not detected. Larvae were to 1 in. in length. The size corresponds to later instar larvae. The speckled green fruitworm has six larval instars. It appears that small larvae are not easy to detect as they must have been present on earlier survey dates, but were not detected. On 17 May, leaf-feeding and fruit-feeding injury were found. Injury was spotty throughout each orchard, but fairly heavy within a tree with injury. Many cherries in a localized area within a tree showed signs of feeding. Many leaves and fruit showed injury on an infested tree. We estimated that 5-10% of the trees in each orchard had fruitworm injury.

The larvae were highly camouflaged and, thus, very difficult to detect. We did not collect any larvae by beating limbs and catching falling debris on beating trays. Evidently, the larvae do not easily release their grasp from limbs, leaves and fruit. Larvae were detected by locating feeding injury and then visually searching until a larva was observed. Larvae were collected and identified in the laboratory using references. Identifications were confirmed by the USU Plant Pest Insect Diagnostician, Alan Roe.

On 5 June surveys, no larvae were detected. Leaf-feeding injury was still present, but not as obvious and feeding had apparently declined. Very few injured fruit were detected. It is likely that injured fruit had already abscised and dropped from the trees. Because larvae were not found, they had likely already moved to the ground to pupate.

The life cycles of the two species vary in that the speckled green fruitworm spends the majority of the summer and over winters as a pupa (June March), emerging as an adult the following spring to lay eggs. The pyramidal fruitworm spends the summer as an adult and then lays eggs in October that overwinter on tree limbs until the following spring.

Based on this limited survey, crop loss from fruitworm feeding did not appear substantial. Controls are only recommended if injury is substantial and populations seem to be building over years. Suggested management practices to reduce populations of both species in infested orchards are:

Pyramidal fruitworm
Speckled green fruitworm
Fruit-feeding injury
Camouflaged larva on a leaf