Excerpt from Publication 310, Integrated Pest Management
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The obliquebanded leafroller, Choristoneura roseceana (Harris), a moth in the Tortridae family, occurs in apple-growing areas across North America. Considered a minor pest in the past, this insect is a major direct pest of apple in Ontario due to its developing resistance to organophosphate insecticides in most commercial orchards. Cross resistance to pyrethroids and certain insect growth regulators is also documented in some obliquebanded leafroller populations.
The obliquebanded leafroller has an extremely wide host range and feeds on all species of fruit trees, hardwoods (e.g. maple, hawthorn and crab apple), grey dogwood and brambles (e.g. raspberry and blackberry).
Eggs are laid on the upper surface of the leaves in patches (7-14 mm) that contain several hundred eggs and resemble small overlapping scales (Figure 4-96).
Figure 4-96. Egg mass laid on the upper surface of leaf
Egg masses are light green to yellowish green in colour. Prior to hatching, contents of individual eggs turn black and the dark head of larva is seen. After hatching, empty egg masses often remain on leaves and appear white against the dark green leaf. Larvae progress through six instars, growing to a final length of 20-30 mm. The body is coloured light green to yellowish green to dark green. The head capsule is usually dark brown or black with a similar coloured segment just behind the head (prothoracic shield). The edge between the head capsule and prothoracic shield is often white or cream (Figure 4-97).
Figure 4-97. Obliquebanded leafroller larva
Pupae are a dark reddish brown, and develop in protected places, often found inside leaves rolled by the larvae (Figure 4-98). Length varies from 11-14 mm.
Figure 4-98. Pupa of obliquebanded leafroller
The adult moth is variably coloured, light tan to dark brown with darker bands on the fore ings (Figure 4-99). Females are larger and generally darker than the males. The wingspan of the males ranges from 16-22 mm, and the female from 24-30 mm. Females are poor flyers, and both sexes are most active at dusk (crepuscular).
Figure 4-99. Adult obliquebanded leafroller
The overwintering generation exists as second or third instar larvae in hibernacula (temporary cocoons) under the bark or in the limb crotches. Larvae become active in early spring (tight cluster to bloom), once temperatures rise above 10ºC, and move to developing fruit spurs and flower buds. As leaves expand, larvae move to new terminal growth where they web and roll up the terminal leaves, hence the name leafroller. This strategy evolved as a defence from predators such as birds, and also serves to protect larvae from insecticide treatments. Pupation usually takes place in early June inside rolled leaves. Moths emerge over a four to five week period from late June through July. Much of the mating and egg laying occurs in the upper portions of the trees, and egg masses are also found in the lower canopy. Newly emerged larvae (or summer generation larvae) disperse from egg masses by crawling to other leaves or dangling from silken threads. Wind currents disperse these ballooning larvae to surrounding trees. These larvae initially feed on leaves in and around terminal growth. By early July, when terminal growth begins to harden off, larvae move to fruit clusters and feed on fruit and adjacent leaves. Larvae then pupate and adults emerge from early August through early September. Adults mate and lay eggs and larvae from this generation are active well into September when enter overwintering hibernacula. The obliquebanded leafroller has two generations a year.
Early season (spring-feeding) activity on buds, leaves and flowers (Figure 4-100) rarely results in economic injury.
Figure 4-100. Feeding damage at the terminals
Overwintering larvae also feed on developing fruitlets, resulting in deep gouges in small apples (Figure 4-101). These fruit often abort around June drop. Fruit that remains until harvest has large russetted indentations and corky scars, indistinguishable from feeding damage by other spring-feeding caterpillars, i.e. green fruitworm.
Figure 4-101. Spring-feeding damage on fruit
Feeding on terminal shoots in spring or summer is only a concern on nursery stock and young non-bearing plantings. The summer generation larvae feed on the surface of fruit often under a leaf or where two apples contact. This damage can be extensive and scab over by harvest, and is often surrounded light coloured areas where leaves were attached (Figure 4-102).
Figure 4-102. Feeding damage from summer generation larva
Late season damage to fruit is characterized by several tiny, or a single circular excavation on the fruit surface where young overwintering larvae chew small holes in the skin of the apple. Late season damage, or pinpoint damage, is often not noticeable at harvest but becomes apparent as flesh around the hole decays or dries out in storage (Figure 4-103). Fruit injury in all cases is most common where two or more fruit are clustered or where a leaf is in contact with a fruit. These areas offer a great degree of shelter to the larvae.
Figure 4-103. Late season damage or pinpoint damage
Although obliquebanded leafroller attack all apple cultivars, some such as Gingergold, Paulared, Jerseymac and other early varieties, sustain greater amounts of damage - perhaps since these varieties are more difficult to thin and have larger leaves. Injury levels of up to 50% are observed on Red Delicious, McIntosh, Ida Red, Golden Delicious, Mutsu, Spartan and Cortland.
Monitoring and threshold
Monitoring techniques for obliquebanded leafroller vary depending on the generation targeted. For overwintering larvae present during the period between tight cluster and petal fall, check 5 terminal shoots and 5 fruit buds in each of 10 trees (50 terminals and 50 fruit buds in total) for signs of caterpillar feeding activity. An insecticide is generally recommended when the action threshold of 1-2 larvae per 100 terminals and fruit buds is observed. Apply an insecticide aimed at the overwintering larvae at petal fall as most larvae are active then. Apply an insecticide in orchards with a history of damage of more than 2% damage in the orchard at harvest the previous year.
Predict the timing and application of products to manage the summer generation with pheromone traps and a degree day model, then follow up with field monitoring for larvae and fruit damage.
After petal fall, four pheromone traps are hung in each 10 ha block at a distance of 30 m between traps along an orchard row. Place in easily accessible areas in block ideally with historically high injury problems. Fasten traps to limbs at eye level where air flow is good. Check traps twice a week and record all moth catches.
The degree day accumulations for the obliquebanded leafroller degree model starts when first sustained moth catch occurs. Using recorded daily maximum and minimum temperatures, daily degree days Celcius (DDC) are calculated using the following equation:
DDC= [(Maximum °C + Minimum °C)/2] - 6.1°C
DDCs are summed each day. At 244 DDC, egg hatch of the summer generation begins and at 433 DDC, 95% egg hatch has occurred. Immature larvae are very small and difficult to see. Larvae initially feed on tender growing terminals, water sprouts and developing fruit. After they reach the third instar, larvae cause more damage to fruit. Monitor for emerging larvae by examining 10 shoots and 10 fruit on 10 trees in a 4 ha block for the presence of larvae or feeding damage. Often damage is more apparent in orchards than are larvae.
Management for the summer generation is recommended if 1% to 2% of terminals or fruit are infested. Resample the orchard in three to five days to ensure the population was not underestimated. Once 240-280 DDC is reached and 1% to 2% of terminals or fruit are infested, an insecticide is recommended. Follow up sprays may be required because of the extended larval emergence of the summer generation (four to five weeks).
A number of parasitic wasps (Ichneumonidae, Braconidae,
Trichogrammidae) and flies (Tachinidae) (Figure 4-104) will attack
obliquebanded leafroller larvae. Where IPM-compatible pesticides
are used, these parasitoids suppress population numbers, but cannot
provide complete biological control.
Figure 4-104. Parasitized larvae with Tachinid pupa
Several cultural practices reduce the severity of injury from obliquebanded leafroller. Diligent chemical and hand thinning of fruitlets to singles make less favourable feeding sites.
Annual pruning to maintain an open canopy improves spray coverage. Avoid excess nitrogen to prevent excessively lush and prolonged vegetative growth that is attractive to obliquebanded leafroller.
Growers have many effective products for sustainable management of obliquebanded leafrollers. Implement resistance management programs to ensure long-term effectiveness of available insecticides. When using chemical control, always use the same insecticide within a generation. When applying an insecticide for both generations, be sure to use a product from a different chemical family for each generation. For more information on the products available to manage obliquebanded leafroller and resistance strategies, see OMAFRA Publication 360, Fruit Production Recommendations.
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