WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Leafroller

Obliquebanded Leafroller (Choristoneura rosaceana) and others

Insects & Invertebrates

 

Leafroller

 

Symptoms

Leafroller larvae feed on leaf and flower buds, opened leaves and blossoms, and ripening fruit. Two generations occur; the overwintering larvae feed on the earlier plant stages and the second generation feeds on leaves and fruit. During feeding, the larvae will roll and tie together leaves, blossoms, and fruit with silk as a protective covering.

On large, established bushes, leafrollers will cause little damage, but may be a contaminant pest in mechanically harvested fields. In fields with younger, smaller plants leafrollers can quickly defoliate entire bushes, causing stunting and undesirable branching of growing points if not located promptly and destroyed.

 

Identification

Several species of leafrollers of the family Tortricidae will attack blueberries, but the Obliquebanded Leafroller (OBLR) is most common in Whatcom County. Adult OBLR moths are small (1/2” long), bell-shaped, and light brown with a darker band across its wings. Mature larvae are about 1” long and are yellowish-green with dark brown or black heads. Young larvae are tan in color. Eggs are laid on leaves in a greenish patch of up to 200 eggs.

 

Leafroller

 

Life History

The obliquebanded leafroller has two generations per year while other related species have one to three generations. Leafrollers overwinter as larvae under loose bark, in twig crotches or in cracks or rough areas. Some moths can start to fly as early as February.

Obliquebanded leafroller larvae resume activity from overwintering in the spring. They spin themselves into tubes in the leaves. When disturbed, they will leave the leaf tube and lower themselves on strands of silk; they may be transported quite a long distance by wind on this silk. Pupation occurs within the leaf tube. Moths emerge from pupation in mid-June to mid-July. Eggs are laid after mating and they will hatch after 10-12 days. New larvae will move to new leaves by crawling or lowering themselves by silk. These larvae will pupate by August, and the next generation of adults is present in August and September. Second generation larvae will overwinter on the host plant or on other nearby plants.

 

Leafroller

 

Monitoring

Pheromone traps are available for OBLR and Orange Tortix. These can help to determine the timing of adult emergence and timing of larvae presence. Place pheromone traps in fields beginning in late April or May and check weekly.  Starting one week after peak flight, leaves should be examined for worm infestation.

Inspect plants thoroughly especially on the field’s outer edges, where the first sign of influx will appear. Look out for rolled leaves and chewed leaves on new growth and blossoms in the early spring.

Degree-days have been determined for OBLR life stages in Michigan. These can be used to predict when to monitor for specific life stages and when effective treatments should be made. Using a base of 43°F, life stage activity is:

Number of Degree Days (base 43)
Life stage
600
First adult emergence
800
First eggs laid
1,150
Peak adult emergence
1,250
Peak egg laying
2,050
First emergence of second generation adults
2,300
First eggs laid by second generation adults

 


Thresholds and Management

Threshold varies according to end product usage and processor. Processors of IQF fruit have zero tolerance for leafroller larvae. Talk to your buyer for their threshold. Consider control if more than 5% of the terminal growth and floral parts have larvae or larval damage.

Unless leafroller numbers are very high, spraying is not necessary. Repeated or unnecessary sprays will harm natural enemies that are present, such as native parasitic and predatory insects and spiders that will reduce their populations.

Applications of target specific bacterium, Bacillus thuringiensis, kurstaki may be used and will not harm bees or other beneficial insects.

Cultural controls such as pruning effectively will help reduce leafroller numbers by removing over wintering sites; effectively weeding fields will remove alternate hosts for this pest.

 

Resources

Michigan State University, Blueberry Facts, Obliquebanded Leafroller
http://www.blueberries.msu.edu/oblique.htm

Michigan State University, Blueberry Facts, Other Leafrollers
http://www.blueberries.msu.edu/leafrollers.htm

Michigan State University Extension, Fruit IPM Factsheet, Obliquebanded Leafroller
http://web1.msue.msu.edu/vanburen/oblr.htm

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu