Obliquebanded Leafroller

Table of Contents

1. Introduction
2. Description
3. Biology
4. Damage
5. Management: Chemical Controls

Introduction

The obliquebanded leafroller, Choristoneura roseceana (Harris), a moth in the Tortidae family, occurs in apple-growing areas across North America. Considered a minor pest in the past, this insect has become the most important direct pest of apple in most of the major apple-growing regions of Ontario due to its developing resistance to organophosphate insecticides (and in some areas, pyrethroids as well). These areas include the regional municipalities of Durham, and Niagara, and the counties of Essex, Kent, Grey, Northumberland and Prince Edward.

The obliquebanded leafroller has an extremely wide host range feeding on all species of fruit trees, hardwoods (e.g., maple, hawthorn, crab apple), grey dogwood, and brambles (e.g., raspberry and blackberry).

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Description

The adult moth is variable-coloured, light tan to dark brown with darker bands on the fore wings (Figure 1). Females are larger and generally darker coloured than the males. The wingspan of males ranges from 10 to 22 mm. Females are poor flyers, and both sexes are most active at dusk (crepuscular).

Figure 1. Adult obliquebanded leafroller.

Eggs are laid on the upper surface of leaves in masses of several hundred and resemble small overlapping scales (Figure 2). Egg masses are from light green to a yellowish green in colour. Prior to hatching, the contents of individual eggs turn black.

Figure 2. Egg mass laid on upper surface of leaf.

The larvae progress through six instars, growing to a final length of 20 - 30 mm. The body can be 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 hear (protroracic shield) (Figure 3).

Figure 3. Obliquebanded leafroller larva.

Pupae are a dark reddish brown and often found inside leaves rolled by the larva (Figure 4). Length varies from 11-14 mm.

Figure 4. Obliquebanded leafroller pupa. 

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Biology

The obliquebanded leafroller overwinters as a second or third instar larva in a hibernaculum (temporary cocoon) under bark or in limb crotches. Larvae become active in early spring (tight cluster to block), once temperatures rise about 10°C. They move to developing fruit spurs and terminal buds where they feed on leaves and developing flower buds. As leaves expand, larvae may move to the new terminal growth where they web and roll up the terminal leaves - hence the name leafroller. This strategy may have evolved as a defense from predators such as birds, but also serves to protect larvae from insecticide treatments. Pupation usually takes place in early June inside rolled leaves.

The first summer generation adults emerge over a four to five week period from late June through July. Research indicates that much of the mating and egg laying occurs in the upper portions of trees, but egg masses can be found in the lower canopy as well. newly emerged larvae disperse from egg masses by crawling to other leaves or by dangling from silken threads. Wind currents disperse these ballooning larvae to surrounding trees. Summer generation larvae initially feed on leaves in and around terminal growth begins to harden off, larvae may move to fruit clusters and feed on fruit and adjacent leaves in these areas. Second summer generation adults are active in August and larvae from this generation are active well into September before eventually forming hibernacula to overwinter in.

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Damage

Early season (spring-feeding) activity on buds, leaves and flowers (Figure 5) rarely results in economic injury. However, overwintered larvae may also feed on developing fruitlets resulting in deep gouges in the small apples (Figure 6). These fruit often abort around the June drop. Those that remain until harvest have large russeted indentations and corky scars, indistinguishable from feeding damage by other spring-caterpillars, i.e., green fruitworm. Summer feeding on terminal shoots is only a concern on nursery stock and young, non-bearing plantings. Fruit feeding comes in three distinct types of damage. The first is termed "pin prick" feeding and consists of a single small sting to the fruit (Figure 7).

Figure 5. Feeding injury to terminal.

Figure 6. Early season feeding injury on fruit.

Figure 7. Pinprick injury made by first summer generation leafroller.

This type of injury generally does not result in grade out at the packing line. The second, called pinpoint feeding, is characterized by several tiny, circular excavations on the fruit surface (Figure 8). The third type of feeding injury is more extensive, shallow feeding resembling external railroading on the fruit surface (Figures 9 and Figure 10). The latter two types of injury are usually graded out at the packing line, depending on the extent or severity of the injury.

Figure 8. Pinpoint injury made by first summer generation leafroller.

Figure 9. Extensive feeding injury by first summer generation.

Figure 10. Late season (2nd summer generation) fruit injury.

Fruit injury is most common where two of more fruit are clustered or where a leaf is in contact with a fruit. These areas offer a greater degree of shelter to the larvae.

Although obliquebanded leafrollers attack all apple cultivars some, such as Paulared, Jerseymac, and other early varieties, sustain greater amounts of damage - perhaps since these cultivars are more difficult to thin and have larger leaves. Injury levels of up to 25% have been observed on Red Delicious, McIntosh, Ida Red, Golden Delicious, Spartan and Cortland.

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Management: Chemical Controls

In apple-growing areas where the obliquebanded leafroller is not resistant to organophosphates, the general monitoring guidelines for spring-feeding caterpillars should be followed:

During the period between tight cluster to several weeks after petal fall, check 10 terminal shoots in each of 10 trees (100 terminals in total) for signs of caterpillar feeding activity. An insecticide is generally recommended when an action threshold of 12-15 larvae per 100 terminals is observed.

Where organophosphate resistance is present the first summer generation is monitored with sex pheromone traps. In Ontario, a Pherocon II diamond trap (or equivalent) is used in combination with a pheromone lure, see Appendix X of Publication 310: Integrated Pest Management for Ontario Orchards for a list of suppliers. Two traps are hung in each 25 acre orchard block at a distance of 30 or metres between traps. Since it is assumed that pesticide resistant populations of obliquebanded leafroller are resident in the orchard, traps do not have to be hung along orchard perimeters. Place in easily accessible areas (along driverows or in blocks with historically high injury problems would be ideal.

Traps should be placed out after petal fall. Fasten traps to limbs at eye level where air flow is good. Check traps twice a week and record all adult moth catches.

Insecticide aimed at the overwintering generation should be applied where leafroller activity begins - generally sometime between pink and petal fall. Timing of treatments for the first summer generation (late June to early July) is just prior to first egg hatch. This even occurs at 170-210 Degree Days Celsius(DDC) (Base 6.1°C) after Biofix (first sustained moth catch in pheromone traps). To calculate, use the following equation:

Recommended pesticides are listed in the Pest Management Decision Guidelines in Chapter Five of Publication 310: Integrated Pest Management for Ontario Apple Orchards.

Several cultural practices may reduce the severity of injury from obliquebanded leafroller. Diligent chemical and hand thinning to single fruitlets may make for less favourable feeding sites of obliquebanded leafrollers.

Annual winter pruning to maintain an open canopy will result in improved spray coverage. Avoid excess nitrogen to prevent excessively lush and prolonged vegetative growth that may be attractive to obliquebanded leafrollers.

A number of parasitic wasps (Ichneumonidae, Braconidae, Trichogrammidae), and flies (Tachinidae) will attack obliquebanded leafroller larvae. Where IPM-compatible pesticides are being used, these parasitoids can help suppress population numbers. However, they cannot be solely relied upon for providing complete biological control.

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