Leafrollers

Four leafrollers in the family Tortricidae, apple pandemis, light brown apple moth, omnivorous leafroller, and orange tortrix, are pests of caneberries. Apple pandemis, light brown apple moth, and orange tortrix occur primarily in coastal areas where they are pests on both blackberries and raspberries while omnivorous leafroller is a pest of these crops primarily in the Central Valley.

Leafroller moths lay elliptical, green eggs on smooth surfaces, such as upper leaf surfaces, berries, or smooth shoots. Eggs are laid in clusters with individual eggs overlapping each other like fish scales. As embryos within eggs develop, eggs turn from green to greenish brown. Newly hatched larvae are less than 0.06 inch (1.5 mm) long, and mature larvae are about 0.75 inch (18 mm) long.

Apple pandemis larvae are green with yellowish green or straw-colored head capsules. Orange tortrix larvae have straw-colored to greenish bodies with a yellowish head capsule and prothoracic shield. Omnivorous leafrollers resemble orange tortrix but have small, white tubercles from which bristles arise along the back and sides of their body. When disturbed, leafroller larvae wriggle vigorously and drop on a fine silk thread. Pupae are creamy-white at first and later turn dark brown. Light brown apple moth larvae are nearly indistinguishable from other leafroller larvae.

Adult moths are about 0.5 inch (12 mm) long. When at rest, leafroller moths position their wings in a bell shape. Orange tortrix moths have light orange-brown to buff colored forewings with a darker V-shaped marking on the midwing. The forewings of omnivorous leafroller moths are dark, rusty brown on the upper half, tan on the lower half; a darker colored band extends outward on the resting moth from the middle of the wings in a V-shaped pattern that separates dark and light areas. The wings of apple pandemis are also banded in color but the center band on the forewings is edged with white. While the adult coloration of light brown apple moth is variable, males may be distinguished from other leafrollers by an extension of the outer wing. Leafroller moths have protruding mouthparts that resemble a snout.

Apple pandemis and orange tortrix both have two to three generations a year, whereas the omnivorous leafroller has four to five. It is not yet clear how many generations a year the light brown apple moth has in California, although there are two population peaks, one in April and another in the autumn, around the beginning of October in coastal areas.

Leafroller larvae feed on fruit and foliage. Foliar injury is generally minor; the primary problem caused by leafrollers is that they get into and contaminate fruit.

Biological control and good sanitation are important factors in reducing leafroller populations. Spray treatments are recommended if the field has a history of leafroller problems or if serious infestation occurred the previous season. Otherwise, use chemical treatments only when determined necessary by careful monitoring.

Mating Disruption

Mating disruption with pheromone-based twist ties is part of a multi-pronged approach to managing light brown apple moth. Other leafroller species can also be managed with a multiple strategy approach because twist tie applications for light brown apple moth are target specific and will not be useful for managing them but the use of insecticide sprays and cultural controls are.

Mating disruption works best when applied over large, continuous areas. Place twist ties across the production field, including nonproduction fields as well if they are mixed in production fields so a larger contiguous area is formed. If possible, place twist ties as far out as the edges of the field or slightly farther, to reduce the probability of a mated female moth flying in from external sources.

The minimum recommended label rate of 200 twist ties per acre appears to reduce light brown apple moth pheromone trap captures to very low numbers. Therefore, where economically possible it is recommended that the twist ties be applied at a rate higher than this, up to the higher end label-recommended rate of 300 twist ties per acre. (For severe infestations, more than 300 twist ties per acre may be warranted, so long as it remains below the maximum threshold allowed on the label.)

Attach twist ties to the upper trellis wire and wrap them doubly around the wire if operations such as pruning and cane adjustment will be taking place. Typically the twist ties last for about 6 months. If in-field monitoring indicates a rise in adult moth finds 3 to 6 months after initial twist tie application, however, this could be an indication of reduced pheromone release by the dispensers. But fluctuations in the moth population over time may also account for such a change, with flight peaks anticipated in the spring around April and a fall population peak between October and November. Following the early spring application, if desired, twist ties may be applied again after harvest to target the fall flight peak.

Insecticides

Supplement the use of twist ties with insecticide sprays to reduce the probability of an in-field light brown apple moth find and to control other leafroller species.

Because caneberry hedgerows are smaller and larval leafroller populations lower in the early part of year, it is recommended that a program of spraying begin in late February to mid-March. Use insecticides such as spinetoram (Delegate), spinosad (Entrust, Success), or B.t. that have a lower impact on beneficials and the surrounding environment, and rotate products to mitigate the potential for resistance to a single pesticide.

Following the initial early season spray, continue to monitor the field for leafrollers. Look for leaf surfaces that are webbed or rolled together, especially those of newly extending laterals. Additionally, look for signs in newly extending laterals for webbing, frass, leaf damage, and the presence of larvae. Another good way to look for leafrollers is to either beat or shake the plants over a bucket or wide, flat container. Carefully sift through the material in the container to detect larvae (early larval instars can be quite small). Concentrate monitoring activities in suspected or previously infested areas.

Any sign of leafroller activity should be a signal to act to protect the crop. It should be emphasized here that the economic threshold for leafrollers in quarantined areas is zero, and subsequently the threshold for spraying is much lower than one would deploy in an integrated pest management program.

Cultural Controls

It is recommended that growers impress upon harvest crews the importance of removing suspect rolled leaves, larvae, and webbed fruit. Considering that crews are passing over every foot of hedgerow at least three times a week during harvest, they can be very effective in reducing leafroller numbers. An incentive program can be implemented to encourage participation with such a campaign of larval removal.

Proper sanitation practices during the dormant season is an essential part of light brown apple moth management. Larvae will overwinter in leaf trash and surrounding weeds. Keep weeds to a minimum and move fallen leaves to the middle of rows where they can be disked into the soil.

Biological Control

Several wasps have been recorded as parasites of omnivorous leafroller including Goniozus platynotae, Trichogramma sp., Cotesia (Apanteles) sp., Microgaster phthorimaeae, Macrocentrus ancylivorus, Cremastus platynotae, Diadegma compressus, Elachertus proteoteratis, and Spilochalcis sp. Two flies, Erynnia tortricis and Nemorilla pyste, are also known as omnivorous leafroller parasites. All are larval parasites, except the Trichogramma sp., which is an egg parasite.

Several parasites also attack orange tortrix. The most common two are Apanteles aristolilae and Exochus sp. An external parasite, Hormius basalis, also occurs. Major parasites of apple pandemis include the parasite wasp, Horogenes sp., and a tachinid fly, Nemorilla floralis.

Also, general insect predators and several species of spiders may influence the leafroller populations by feeding on eggs or larvae. Some insect predators are green lacewing (Chrysoperla carnea), minute pirate bug (Orius tristicolor), and damsel bug (Nabis sp.). Spiders in the family Theridiidae are common predators.

Cultural Control

Proper sanitation practices during the dormant season help prevent a buildup of leafrollers. Most overwintering larvae survive in surrounding weeds or in trash beneath the canes. Destroy weeds and move trash to the middle of rows where it will be disked into the soil.

Organically Acceptable Methods

Cultural and biological controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on organically certified crops.

Monitoring and Treatment Decisions

Begin monitoring for the leafrollers in early spring by examining plants for larvae. Larvae may web leaf surfaces together, especially those of newly extending laterals, and live between them. Or they may roll leaves and live in the folds. One way to evaluate infestation level in early spring is to carefully inspect newly extending laterals for webbing, frass, leaf damage, and the presence of larvae. Another good way to look for leafrollers is to agitate the hedgerow, either by beating or shaking the plants, and collect the fallen material into a bucket or wide, flat container. Carefully sift through this material to detect larvae (early larval instars can be quite small). Concentrate monitoring activities in suspected or previously infested areas.

Pheromone traps placed in caneberry plantations can be good indicators of moth flight activity and may help to pinpoint when the most intensive monitoring for larvae should be done. Concentrate examinations of the plants in those periods after flight peaks when larvae are increasing in number.

It is especially important to thoroughly inspect plants 7 to 10 days before the beginning of harvest to determine the need for treatment. Large numbers of larvae detected at this time increase the chance of having larvae in harvested fruit, and these odds should be reduced.