Description of the Pest
Several leafrollers in the family Tortricidae are present in strawberry and vegetable-growing areas of the Central Coast. Of these species, the garden tortrix is the most likely to be found feeding on strawberry fruit. The orange tortrix and apple pandemis are primarily foliar feeders. The light brown apple moth, an introduced species, was first detected in the San Francisco and Monterey Bay areas in spring 2007.
Some leafrollers have only one generation in a year, but most leafrollers that feed on strawberry foliage have 2 to 4 generations a year, depending on species and location. When disturbed, these leafroller caterpillars wriggle vigorously.
The adult garden tortrix is a buff-brown moth that is about 1/4 inch (6 mm) long. Each of the forewings is marked with a dark brown diagonal stripe and a marginal spot producing a chevron pattern when at rest. A faint whitish line borders the anterior edge of the brown stripe. This character and the overall lighter color distinguish adult garden tortrix from orange tortrix. The slender caterpillars of the garden tortrix are nearly 1/2 inch (13 mm) long when mature. Caterpillars have light brown to green bodies and light brown heads. The head has a small, distinct dark brown spot on each side. Larvae and pupae overwinter in debris around the base of the plant.
Orange Tortrix and Apple Pandemis
Adult orange tortrix and apple pandemis moths are about 1/2 inch (13 mm) long. Orange tortrix moths have light brown forewings. Apple pandemis moths have a series of lighter and darker rust colored V-shaped bands with the center band on the forewings edged with white. Apple pandemis caterpillars are green with yellowish green or straw-colored head capsules. Orange tortrix caterpillars have straw-colored to greenish bodies with a yellowish head capsule and prothoracic shield.
Light Brown Apple Moth
In both appearance and behavior, the light brown apple moth is similar to the other leafroller species. Adults are light brown, about 1/4 to 1/2 inch (6–13 mm) long and display variable patterns of dark brown on the wings. Like other tortricid moths, they have the typical bell-shaped wings while at rest. The caterpillar is pale to medium green and has a light brown head capsule. Fully-grown caterpillars are 1/2 to 3/4 inch (10–19 mm) long.
Updated information on light brown apple moth and regulatory quarantine procedures in California can be found at your county Agricultural Commissioner's office.
Most leafroller larvae, including the light brown apple moth, tie one or more strawberry leaves together with white webbing to create shelters. Larvae can also create shelters by folding leaves or the sepals of the calyx to fruit and may feed from these sheltered areas on the surface or internal tissues of fruit.
Early in the season, the garden tortrix serves a valuable function in breaking down and recycling old leaf and fruit litter. It generally does not cause significant damage when strawberry plants are small. However, as the leafroller numbers increase and the plant canopies close in, more ripening berries come in contact with trash where they may become exposed to the tortrix larvae. When this happens, larvae will often spin a nest in creases along the berry's surface and may chew small, shallow holes in the berry, incidental to their scavenging. Thus, as numbers increase in late spring or early summer, significant fruit losses can result from both larval contamination and secondary rots invading the feeding holes. During late June and July, contamination of south coast fields just before the berries are sent to the processors can be a serious problem. Fruit damage can appear similar to that caused by other Lepidoptera larvae including corn earworm, armyworms, and cutworms.
The light brown apple moth is unique; although damage caused is similar to other leafrollers, its detection in strawberry fields will result in restrictions shipping fruit out of the quarantine area.
In areas with a chronic tortrix problem, it may be feasible to remove accumulated trash in spring around the plants to limit the potential for a large increase in leafroller numbers. This is especially important in summer plantings and second year fields where it is more likely for leafrollers to be present.
Because it is difficult to distinguish the light brown apple moth larvae from other leafrollers in appearance and behavior, a preventive approach, consisting of sanitation, monitoring, and chemical treatments, targeting all leafrollers is currently suggested for strawberry fields within quarantine zones. This will ensure that no larvae will be present in harvested fruit. This approach will avoid shipment delays and possible loss of fruit marketability.
Organically Acceptable Methods
Remove dead vegetation from strawberry fields to reduce overwintering populations. Use sprays of Bacillus thuringiensis and the Entrust formulation of spinosad on organically certified strawberries. Sprays of Bacillus thuringiensis can be more effective if applied multiple times at close intervals, because it exposes survivors of previous applications to another dose of this insecticide. Additionally, it can be helpful to lower water carrier volumes to concentrate the dose of the insecticide ingested by the larvae.
While the USDA–CDFA regulatory regime is in place for light brown apple moth, the use of mating disruption pheromone dispensers (Isomate LBAM Plus, Pacific Biocontrol Corporation) is strongly recommended for management and reduction of light brown apple moth in organic strawberry. The ‘twist ties' type of dispensers should be applied evenly at the rate of 200 to 300 dispensers per acre above the canopy by attaching them to wires or tall sticks across the field.
Monitoring and Treatment Decisions
There are several ways to monitor for leafrollers, including the light brown apple moth.
In the spring, before the commencement of harvest, begin monitoring by examining plants for larvae. Leaf rolls made by larvae are not hard to find and tend to consist of one or more (usually mid-aged) strawberry leaves webbed together. If a leafroller or the concomitant webbing is detected, it is recommended to search more thoroughly in the immediate vicinity of the initial find, because leafrollers often aggregate. Larvae in fruit can be detected during harvest. The infested fruit and larvae should be destroyed. Webbing under the calyx, frass, or holes in the fruit, all indicate leafroller activity. Fruits have to be observed closely, since early leafroller instars are exceedingly small and can hide under the calyx.
With all leafrollers, directed sprays that penetrate the foliage canopy at a sufficient volume are recommended. Because of the tendency to have overlapping generations, it is difficult to target a specific larval stage.
Garden tortrix larvae are particularly difficult to control with sprays, because they are found in the litter beneath the protective canopy of strawberry leaves.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Success)||4–6 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: Most effective against younger larvae. Rotate to an insecticide with a different mode of action after two successive applications. Maintaining proper pH of the spray tank water is critical for maximum efficacy. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Coragen)||3.5–5.0 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|C.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: Spray when armyworms are still small. To be effective, Bacillus thuringiensis must be applied no later than the second instar stage.|
|(Intrepid 2F)||6–12 fl oz||4||3|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|(Radiant SC)||6–10 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: Rotate to an insecticide with a different mode of action after two successive applications (Success and Entrust have the same mode of action). Maintaining proper pH of the spray tank water is critical for maximum efficacy. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|(Diazinon AG600 WBC)||12.75 fl oz/100 gal water||72 (3 days)||5|
|MODE-OF-ACTION GROUP NUMBER1: 1B|
|COMMENTS: Do not allow this pesticide to run off into surface waters. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|#||Acceptable for use on organically grown produce.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|1||Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).|