Obliquebanded Leafroller

Obliquebanded leafroller larvae are yellowish green caterpillars. They are difficult to distinguish from fruittree leafrollers, which may also be present during bloom. When disturbed, they wiggle backwards and drop to the ground on a silken thread. Rolled leaves webbed together to form protective nests indicate the presence of leafroller larvae. Adult moths have dark brown bands running at oblique angles across their wings. Obliquebanded leafroller overwinters as larvae under bud scales of twigs; in the Central Valley there are two to three generations each year.

Damage to prunes is primarily a concern for fresh market fruit growers. Larvae feed on prunes but generally do not cause serious economic damage unless brown rot invades the feeding wound.

Dormant treatments and bloom time applications for other pests help keep leafroller populations under control. Leafroller damage is not a problem for prunes grown for the dried market but needs to be monitored on fresh market prunes from bloom to petal fall each season so that prompt action can be taken if damaging populations develop. Throughout the season, watch for the presence of leafrollers while monitoring for other pests. This is especially important in orchards where bloom time sprays and pheromone confusion are used to control peach twig borer and oriental fruit moth.

A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack leafroller larvae. General predators such as lacewings, assassin bugs, and minute pirate bugs may feed on eggs and larvae. Preservation of natural enemy populations is an important part of keeping leafroller numbers low. Use selective materials that are least disruptive of biological control when treating other pests.

Organically acceptable management tools include biological control and sprays of oil, the Entrust formulation of spinosad, and Bacillus thuringiensis.

Delayed dormant oil sprays generally help reduce populations as does a Bt program aimed at peach twig borer. When applying dormant oil or dormant oil plus an insecticide, wait until bud break in order to control larvae as they emerge from their overwintering site. You can also treat effectively during the green bud stage. To identify caterpillars present at bloom, view photos.

Postbloom treatments

Monitor obliquebanded leafroller postbloom by putting out pheromone traps and sampling developing fruit. Put out pheromone traps by April 15. (The lower load rate pheromone lures are the best indicators of population levels.) For more information see PHEROMONE TRAPS and record results on a monitoring form (PDF). Begin accumulating degree-days (DD) once moths have been caught in pheromone traps on two or more consecutive observation dates (the biofix). Use a lower threshold of 43°F and an upper threshold of 85°F (vertical cutoff). Begin sampling fruit at 930 DD from the biofix. Visually inspect 15 fruit from each of 80 trees per monitored orchard (a 1200 fruit sample) by walking around trees and looking for larvae or larval damage. Be sure to look for leaf rolls and on fruit where fruit-to-fruit contact occurs and where fruit are touching leaves. For each tree, record both the number of fruit with live larvae and fruit that have been damaged. Use a monitoring form (PDF) for this procedure.

Calculate degree-days for obliquebanded leafroller in prune for your location using the obliquebanded leafroller pest model or degree-day table. To learn more about using degree-days to time insecticide applications, watch the degree-days video.

Treat dried plums if over 2% (or more than 24 fruit) of the total fruit sampled have obliquebanded larvae and/or larval damage present. For fresh market prunes, treat if any larvae or damage is present.

Fruit damage sample

In mid-July, take a fruit damage sample to assess the overall effectiveness of the current year's IPM program and to determine next year's needs. For more information, see FRUIT EVALUATION AT HARVEST. Record on a monitoring form (PDF) the number of fruit infested by larvae, type of larvae present, whether the damage is surface feeding only or if the larvae penetrated the fruit.

• Degree-day calculator
• Degree-day table
• Final fruit damage form evaluation for caterpillars, scale, and aphids (PDF)
• Fruit monitoring form to determine the need for in-season control of obliquebanded leafroller (PDF)
• Photos of leafrollers and other caterpillars
• Sampling for insects monitored using pheromone traps and degree-days (PDF)
• Using degree-days to time insecticide applications