Several important tree fruit pests belong to the group of insects called leafrollers. The common name comes from the larval habit of rolling or tying leaves together when constructing feeding sites or shelters. Pandemis leafroller (Pandemis pyrusana) and obliquebanded leafroller (Choristonuera rosaceana) are the species most commonly found in commercial orchards. Both species have two generations per year. The fruit tree leafroller (Archips argyrospilus) and European leafroller (Archips rosanus) have only one generation per year and are not commonly found in commercial orchards.

The leafroller that occurs most often in mature apple orchards in Washington is pandemis leafroller. In the late 1940s and early 1950s growers reported pandemis leafroller feeding on cherry, apricot, and apple in Yakima and on cherry in the Wenatchee area. During the past 15 years, growers have observed pandemis leafroller with increasing regularity in cherry and apple orchards of the Yakima valley and in north central Washington. More recently, growers have reported it as a pest of peach in the Yakima area. Because pandemis leafroller has occurred only sporadically in the past, most fruit growers are unfamiliar with this pest and do not know how to manage it.

The obliquebanded leafroller is a problem in newly planted apple orchards or in young orchards just beginning to bear fruit. It has not been a serious problem in apple orchards that receive regular insecticide treatments for codling moth, except in mature orchards in the Columbia Basin. In the eastern United States this leafroller is a pest in apple orchards and has developed resistance to organophosphate insecticides. It is the most common leafroller pest of apple and cherry in Oregon.

The obliquebanded leafroller moth is generally larger, 3/4 to 1 inch in length, and darker than the pandemis leafroller. The banding pattern on the wing is similar, but the leading and trailing edges of the wing bands are darker than the remainder of the wing (Fig. 2), not lighter as in the pandemis leafroller.

Pandemis leafroller and obliquebanded leafroller females lay eggs in masses of 50 to 200 on the upper surface of leaves. At first, the egg mass is a light green color (Fig. 3), but as the eggs mature the mass turns light brown. Just prior to hatching, the dark head of the small larva can be seen in each egg. After hatching, egg masses often remain on leaves and are much more visible, appearing white on the dark green background of the leaf.

The young larva of both the pandemis leafroller and obliquebanded leafroller has a green body, but the head capsule and thoracic shield (the segment just behind the head capsule) may range in color from light brown to black (Fig. 4). The more mature pandemis leafroller larva has a light green body and a light green (most common) to light brown head capsule and thoracic shield (Fig. 5). Distinguish the mature pandemis leafroller larva from fruit tree leafroller or obliquebanded leafroller larvae by comparing colors of the head capsule and thoracic shield. All have a green body. The head capsule of the mature obliquebanded leafroller larva is brown to black, while the thoracic shield varies from brown to a dull green color. The sides of the thoracic shield are dark brown to black (Fig. 6). The mature fruit tree leafroller larva is often confused with the obliquebanded leafroller larva. It may be necessary to rear larvae to the adult stage to be certain of the species. The head and thoracic shield of the fruit tree leafroller are black, except for the front margin of the thoracic shield, which is sometimes white. The fruit tree leafroller is usually smaller than the obliquebanded leafroller.

It is extremely difficult to determine which leafroller species is present in an orchard when only young larvae are present. Characteristics of mature larvae are more stable and distinctive and are more useful for determining species. Leafroller larvae most often occur either inside a leaf that has had one side folded and attached to the other, between two leaves attached together, or beneath a leaf attached to an apple with silk webbing. When disturbed, the leafroller larvae wiggle rapidly backwards, often dropping from their shelter on a slender thread. The behavior of the fruit tree leafroller in this regard tends to be more violent than the behavior of the other two leafroller species and can be another clue in identifying the species present in an orchard.

The pupa of both the pandemis and obliquebanded leafrollers is a typical moth chrysalis. The pupa is light green or greenish brown in color (Fig. 7) at first, turning completely tan after a short period of time and later turning a darker brown. The pupa develops in a protected place, usually in a folded and webbed leaf. Since the pupae of all leafrollers encountered in an orchard appear similar, they are not helpful in determining species. Holding the pupa in a container for a few days until the moth appears makes species identification easier.

The pandemis leafroller feeds on many tree fruits, including apple, cherry, pear, prune, plum, and apricot. In 1989, Washington growers observed pandemis leafroller feeding on peach in the Yakima area and created a new host record in Washington. Where pandemis leafroller is a problem in apple, large populations often have occurred previously in nearby cherry orchards. This association is an important factor when growers try to determine what orchards are at risk from leafroller infestation. Young apple and prune orchards have also been implicated as potential sources.

Pandemis leafroller larvae have been collected from several wild host plants, including cottonwood, rose, willow, dogwood, hawthorn, antelope brush, big leaf maple, chokecherry, lupine, and alder. In general, low numbers of pandemis leafroller larvae occur on these hosts. While wild hosts may provide a reservoir for infestation of commercial orchards, their impact is not as great as nearby fruit orchards.

The obliquebanded leafroller appears most often in young apple orchards. While it also occurs in unsprayed pear and cherry orchards, it does not occur commonly in commercially sprayed orchards. The obliquebanded leafroller survives on a wider range of plants than do the pandemis or fruit tree leafrollers. In the eastern United States and Canada this leafroller occurs on 50 to 80 different plants, including conifers. The obliquebanded leafroller uses the same host plants as the pandemis leafroller but could use other plants not mentioned above.

APPLE: Larvae of both species feed primarily on foliage, a habit which has no economic impact on mature trees. The primary economic impact occurs when larvae feed on fruit. This usually occurs when larvae inhabit foliage close to or touching fruit or when fruit occurs in clusters. Such situations increase the chance of a larva attaching a leaf to an apple or using fruit clusters as a sheltered feeding site. Larvae do not appear to seek out fruit for feeding. It is impossible to distinguish fruit damage by young pandemis leafroller larvae from that by young obliquebanded leafroller larvae. Older obliquebanded leafroller larvae sometimes cause deeper and more extensive feeding damage to fruit than do pandemis leafroller larvae.

Pandemis leafroller and obliquebanded leafroller larvae feed on fruit at three times during the growing season. First, larvae of the overwintering generation may feed on fruit in clusters in early to mid-May, consuming portions of young fruit. If these fruit do not abort, the feeding damage leaves them deeply scarred and often severely deformed. The second period for fruit damage occurs during late June and early July. Young summer generation larvae attach a leaf to the apple surface and feed on the apple. Either pandemis or obliquebanded leafroller larvae can cause damage at this time, characterized by shallow feeding usually less than 1/l6 of an inch deep (Fig. 10).

Feeding areas usually are not contiguous but occur as several separate feeding sites within a small area. As larvae grow they tend to move from the interior fruiting canopy and feed on foliage of growing shoots. However, more extensive feeding damage can occur during summer if larger larvae continue feeding on fruit. This type of fruit damage may be more common on varieties such as Granny Smith, and usually has been observed where obliquebanded leafroller is present (Fig. 11). Feeding sites made at this time of year are scabbed over by harvest and are often associated with a lighter colored area on the fruit where a leaf had been attached.

The third period when feeding damage occurs is just prior to, and during, harvest. Larvae of the overwintering generation emerging from egg masses in late summer may attach a leaf to a fruit and feed on it. This feeding damage is often difficult to detect. The young larva chews a small hole through the skin of the apple and then feeds on a small quantity of apple flesh directly beneath the entry site. Two or more of the "pin hole" feeding sites may occur within a small area. Decay or drying of apple flesh around feeding sites during storage makes them much more visible. This type of damage is often mistaken as codling moth damage.

The distribution of leafroller larvae and their associated damage depend on tree size and type. In large trees, two to four times more larvae may occur in the upper half than in the lower half. Spur varieties tend to have more fruit damage than nonspur varieties at the same larval densities. The closer association of fruit and foliage in spur varieties increases the likelihood of leaves contacting fruit, thus providing larval feeding shelters for the pandemis leafroller.

CHERRY: The pandemis leafroller frequently infests sweet cherry orchards. Young leafroller larvae found in fruit have been mistaken as cherry fruit fly larvae until examined more closely. Reduced spray programs after cherry harvest allow development of both pandemis and obliquebanded leafroller, making it possible for large populations to build up and affect nearby apple orchards. Orchards in The Dalles, Oregon, have reported some severe damage to cherry from obliquebanded leafroller.

Pheromone traps can be used to monitor the activity of male pandemis and obliquebanded leafrollers. The pheromone used to monitor the pandemis leafroller is that of the three-lined leafroller, Pandemis limitata. This moth is a close relative of the pandemis leafroller. Its pheromone, essentially the same, works well for monitoring pandemis leafroller. When moderate to high populations of leafrollers are present in an area, traps may quickly become saturated (filled with moths). This makes it difficult to determine peak activity periods by using traps, unless they are checked every day. After a capture of 50 or more moths in a trap, install a new trap bottom. Moth capture in pheromone traps has not been a good indicator of potential leafroller damage. Pheromone trap captures of 15 or less moths per week usually, although not always, indicate little potential for leafroller damage, but higher capture levels do not always mean that damage will occur. Male leafroller moths may travel considerable distances and thus influence moth capture at locations where chances of larval infestations are low.

Sampling for the presence of leafroller larvae is labor intensive. In the spring examine flower buds as they open (delayed dormant period of apple) to determine when larvae have left the hibernacula and have begun feeding. Examination of 100 fruit buds from an orchard should give a reasonable indication of the presence and relative density of leafroller larvae (Fig. 4). Examine buds with magnification, as the larvae and their feeding damage are difficult to detect. As the flower buds expand and larvae grow, their presence is more obvious because of webbing on the flower parts (Fig. 12). Young larvae present in late June or early July are difficult to detect. They remain in the fruiting canopy, spinning a small webbed shelter near the mid-vein on the under surface of a leaf or attaching a leaf to a fruit, feeding on both. As larvae grow, they migrate to growing points in the tree — water sprouts and shoots — and feed on leaves toward the tip (Fig. 13). Examining shoots in late July provides the easiest means of determining leafroller presence in the orchard; unfortunately, it is too late to take action to prevent most fruit injury. It may indicate the need for action to protect fruit prior to harvest.

Researchers in Washington have conducted little research on the chemical control of obliquebanded leafroller. In general, the recommendations for pandemis leafroller control are considered applicable to control of obliquebanded leafroller.

The appropriate choice of insecticide, proper dose, and timing are keys to successful use of any insecticide. Some insecticides give poor leafroller control, while others give control relative to the dose used. Consult the current Washington State University publication EB0419, Crop Protection Guide for Tree Fruits in Washington, for recommendations on insecticides to use for leafroller control. To achieve the best control of pandemis leafroller larvae emerging from overwintering hibernacula, apply insecticides at the delayed dormant stage of apple flower bud development (bud development chart stage 3). Sprays applied earlier or later than this period have given inconsistent control results.

During summer, direct insecticides against adults timed at peak flight (June 10-25 or mid- to late August). For controls to be effective against young larvae, apply treatments during late June or early July, after egg hatching is complete. Control of older larvae during late July and August has been difficult. This late-season treatment will give only a limited suppression of leafroller populations. Consider it, at best, only a salvage operation to help reduce fruit damage at harvest.

Control of summer generation adults during August is complicated by the relatively long period of adult activity. It is extremely difficult to time sprays properly and still remain within label restrictions for the preharvest intervals. The best timing is at peak adult flight, which can occur from mid-August to early September. Because of pre-harvest interval (PHI) restrictions, growers cannot use many insecticide products at this time. Late season sprays are discouraged in Washington because of detrimental effects on natural enemies of aphids.

Jay F. Brunner, Ph.D., Washington State University entomologist, and Elizabeth H. Beers, Ph.D., Extension Entomologist, WSU Wenatchee Tree Fruit Research & Extension Center.

Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Issued by Washington State Cooperative Extension, F. L. Poston, Director, and the U. S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, national origin, religion, gender, age, disability, and gender preference. Trade names have been used to simplify information; no endorsement is intended. Published December 1990. C

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