OBL.jpgObliquebanded Leafroller, Choristoneura rosaceana (Harris)

I. Introduction: The obliquebanded leafroller (OBLR) is native to and widely distributed throughout temperate North America. Larvae feed on a wide range of plants including unrelated deciduous trees (e.g., larch). Their importance is increasing in the northeastern U. S. due to the development of resistance to certain organophosphate insecticides. There are two generations a year.

II. Hosts: Although the OBLR can feed on a wide range of plants, their preferred hosts are members of the rose family. Outbreaks can occur on apple, peach, nectarine, cherry and pear trees.

III. Description: Adults are approximately 3/4-1 inch (19-25 mm) long and have a wingspan of 1 inch (25 mm). Their forewings are reddish brown crossed by three alternating light and brown bands (Plate 26). The hind wings, invisible when the moth is at rest, are pale yellow. The female moth is large and more distinctly marked than the male. A female can lay up to 900 eggs during her 7- to 8-day oviposition period. Eggs are laid on the upper surfaces of leaves. They appear as greenish, yellow masses measuring about 3/16 x 3/8 inch (5 x 9.5 mm) and may contain 200 or more eggs. The black head capsules of embryonic larvae become visible prior to hatching, which usually occurs in 10 to 12 days. Larvae are indiscriminate feeders that pass through six instars. Newly hatched larvae have a yellowish, green body and a black head and thoracic shield. Mature larvae are approximately 1 inch (25 mm) long, and the head and thoracic shield may either be black or various shades of brown (Plate 27). These larvae can be confused with larvae of the fruittree leafroller. Pupae are dark brown, about 1/2 inch (12.5 mm) long, and are usually found in rolled leaves on the tree. Occasionally a species resembling obliquebanded leafroller occurs in pheromone traps of variegated leafroller. There is little overlap in the pheromone blends of these species. The moths in the VLR traps are actually a species related to obliquebanded leafroller, the spotted fireworm, Choristoneura parallela (Robinson). Spotted fireworm wings possess a dark spot on the leading edge, about a third of the length from the base, absent on obliquebanded leafroller wings.

IV. Biology: The OBLR overwinters as either second or third stage larvae within a silken case, or hibernaculum. These hibernacula can be found in the protected areas of the scaffold limbs (e.g., pruning scars). The larvae become active in the spring as the buds begin to open. They begin to feed by tying together a number of leaves with silk. Overwintered larvae feed first on watersprouts and then move throughout the tree. Those feeding on developing flower buds do so before bloom and continue to consume floral parts throughout the blossom period. After petal fall, these larvae continue to feed on developing fruit. Pupation occurs within these sheltered areas with the first adults observed during late May and early June. The first summer brood of larvae emerge and complete development in mid to late July. Newly hatched larvae of the first summer brood move to and feed on tender growing terminals, watersprouts, or developing fruit. As these larvae reach the third instar they display an increasing propensity to damage fruit. Second-brood eggs begin to hatch in early to mid-August and feed until they reach the third instar in fall, when they construct hibernation sites on twigs or bark and enter winter diapause. These second-brood larvae feed primarily on leaves until they enter diapause, although they may occasionally damage fruit.

V. Injury: Larvae primarily feed on foliage, a habit which has no economic impact on mature trees, but can seriously reduce leaf area and growth on nonbearing trees. Feeding on the developing fruit can occur at three times during the season. The first period occurs at pink through the petal fall and shortly thereafter. This feeding injury can cause fruit to abort or result in deeply scarred fruit (Plate 28). The second feeding period occurs during July when the larvae can attach a leaf to the surface of the fruit and feed. This injury is characterized by shallow feeding usually of less than 1/16 inch (1.6 mm) deep. More extensive injury may occur if larger larvae continue to feed on the fruit. Feeding injury at this time of the season may become scabbed over by harvest. The third feeding period occurs, just before, or during harvest. The type of injury caused is similar to that caused by the tufted apple bud moth, that of "pin-holing".

VI. Monitoring: The flight of the male adults can be monitored with sex pheromone traps. This information can be used to predict when the various stages of OBLR may be present for timing sprays (see below). However, since the males are capable of traveling long distances, sex pheromone traps cannot be used to predict population size. Scientists at Cornell University have developed a sequential sampling plan for monitoring larval populations and determining population size. Sequential sampling utilizes the results of the samples that are being evaluated to determine the total number of samples to be taken. The following is taken from the Cornell 1993 Pest Management Recommendations for Commercial Tree-Fruit Production.

Figure 6 presents a sequential sampling chart for OBLR monitoring at bloom. Examine 10 bud clusters or expanding terminals per tree for live larvae. Sample from random trees that are representative of the entire block. Do not count actual numbers of larvae in an infested cluster, damaged clusters that have no larvae in them, or clusters containing only dead larvae. Choose half of your clusters or terminals from the inside the tree canopy, and the other half from near the outside of the canopy. As you proceed from tree to tree, compare the number of clusters containing live larvae with the limits given in the figure. Continue sampling as long as you are between the two values given for the respective number of samples taken; stop sampling when you reach one of these values. This could occur by the time 10 clusters have been sampled if 2 are infested, or after 60 clusters have been sampled and you remain between the values. A result of "Stop Sampling and Treat" means that an appropriate insecticide should be incorporated into the petal fall spray. "Stop Sampling, Don't Treat" means that the larval population is not high enough and should not be considered when choosing insecticides for the petal fall spray. If you are at "3" by the 100th cluster, consider your infestation level below the threshold.

Figure 8 presents a sequential sampling chart for obliquebanded leafroller monitoring for the first summer generation. Sample at approximately 600 DD (43�F) after the first adult flight in your area. Traps should be hung by the end of May or early June depending on the locality. Examine 10 expanding leaf terminals per tree, selecting trees from as wide an area of the block as possible. If trees are >3 m (>10 ft) tall, an effort should be made to include some clusters from the mid- to upper canopy area, or from watersprouts, which are favored infestation sites. Try not to bias your sample by picking clusters that you suspect are infested. Record the number of clusters that are infested with live larvae, not the number of live larvae. Continue sampling until you reach one of the staircase lines in Figure 3. If you reach the intersection of the two lines by the 100th cluster, this is equivalent to a Don't Treat decision. If you reach a Treat decision, an insecticide spray is recommended at this time. If you reach a Don't Treat decision, return in 3-5 days (100 more DD) and repeat the sample; a Don't Treat decision the second time indicates that no treatment is recommended. Cornell University utilizes a 3% threshold at bloom (Figure 6) and 3 (Figure 6) and 10% (Figure 8) thresholds for fresh and processing fruit, respectively, for the first summer generation.

This is taken primarily from a chapter by L. A. Hull, D. G. Pfeiffer & D. J. Biddinger on apple direct pests, reprinted with permission from Mid-Atlantic Orchard Monitoring Guide, published by NRAES, 152 Riley-Robb Hall, Ithaca, New York 14853-5701.

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