How to Manage Pests
UC Pest Management Guidelines
Several leafrollers in the family Tortricidae are present in vegetable growing areas of the Central Coast. In particular, garden tortrix, light brown apple moth, and orange tortrix are pests of cole crops.
Adults of these leafrollers have:
|garden tortrix||light brown apple moth||orange tortrix|
|adult||1/4 inch (6 mm)||1/4 to 1/2 inch (6–13 mm)||1/2 inch (12 mm)|
|larva (full grown)||1/2 inch (12 mm)||1/2 to 3/4 inch (12–18 mm)||1/2 inch (12 mm)|
Although not well studied on cole crops, most leafrollers have one to four generations a year, depending on species and location.
Females lay eggs masses of 20 to 170 eggs per batch on smooth surfaces, such as shoots or upper leaf surfaces. Egg masses are difficult to find and are composed of elliptical eggs that overlap each other like fish scales. Eggs vary in color, but are often light green initially and turn from green to greenish-brown as the embryos develop .
When disturbed, leafroller caterpillars wriggle vigorously, suspend themselves from a silken thread, and drop to the ground. Larvae and pupae overwinter in debris around the base of the plant.
Like the orange tortrix, adult garden tortrix forewings are marked with a dark brown diagonal stripe and a marginal spot that produces a chevron (V-shaped) pattern when at rest. However the chevron pattern on the adult garden tortrix is darker than that of the orange tortrix, making it more noticeable. Garden tortrix also has a light-colored margin on the edge of the chevron that orange tortrix lacks.
Garden tortrix larvae are slender, with light brown to green bodies and light brown heads. The head has a small, distinct, dark brown spot on each side, as well as a darkened prothoracic shield (the top of first segment behind the head).
The adult orange tortrix, is also called apple skinworm. The female moth generally has a faint V-shaped marking located midwing. The male is similar to the female except that it has darker markings. Compared to the garden tortix, the V-shaped pattern is less visible.
At hatching, larvae are 0.2 inch (2 mm) long. Older larvae have greenish to straw-colored bodies with a yellowish or straw-colored head capsule and prothoracic shield. Larvae usually feed singly on shoot tips or on succulent leaves in nests they web together with silk. Larvae make a dense silken cocoon in webbed foliage and pupate. Adults emerge in about 1 to 3 weeks depending on temperature. Orange tortrix has two to four generations per year with all stages present throughout the year.
The size of the moth may vary during the season with larger individuals during cool wet months and smaller individuals during warm dry months. The length of a resting moth is about half its wingspan. Distinguish light brown apple moth from the other two leafrollers by the extension on the outer edge of the forewing (costal fold). Females do not have the costal fold. Also, in contrast with garden tortrix and orange tortrix, light brown apple moths display a variable dark brown pattern on the wings, especially males. The larva is pale to medium green and has a light brown head capsule.
Moths emerge after 1 to 3 weeks of pupation and mate soon after emergence. They stay sheltered in the foliage during the day, resting on leaf undersides. Females begin to lay eggs 2 to 3 days after emerging, depositing them at night on the upper side of leaves.
Overwintering larvae do not have a winter resting stage (diapause). They pass the winter as second- to fourth-stage larvae on vegetation surrounding the field or on weeds. Larvae may survive for up to 2 months in the winter without feeding.
A degree-day model indicates that there will most likely be two generations a year in the central and north coast areas of California and three or four generations a year in the Central Valley and Southern California. Completion of the entire life cycle requires 620 degree-days above 45ºF.
Light brown apple moth, also known as LBAM, is an introduced species native to Australia that was first detected in the San Francisco and Monterey Bay areas in the spring of 2007. Subsequent detections have occurred in coastal California from Los Angeles to Sonoma counties. In its native range it does not survive well at high temperatures, but it does thrive in cooler areas with mild summers, moderate rainfall, and moderate-to-high humidity. Updated information on light brown apple moth can be found on the UC IPM website. Because it is a quarantined pest with special requirements regarding movement, inspection, and treatment of regulated plant materials, consult the California Department of Food and Agriculture (CDFA) website or the county agricultural commissioner's office for compliance information.
Leafrollers are polyphagous (feed on many kinds of plants). Cole crops near native vegetation, riparian, and urban areas may have an increased risk for leafroller infestations because adults developing on wild hosts or landscape plants occasionally migrate to cole crop fields and lay eggs.
Direct feeding damage of leafrollers is minor on cole crops because leafrollers rarely infest the economic portion of the crop, such as the florets. Typically, most leafroller larvae, including light brown apple moth, tie one or more leaves together with webbing to create shelters and may feed from these sheltered areas on the leaf surface.
The main economic cost of leafrollers is the detection of light brown apple moth in a field. Because it is a quarantined pest, detection may result in difficulties shipping produce out of quarantined areas.
Light brown apple moth is a class A rated pest subject to quarantine, so there is zero tolerance for larvae in fields or on harvested crops. Fields within a light brown apple moth quarantine area are managed differently for leafrollers than fields outside quarantine areas.
Early weed control can help to reduce leafroller numbers. However, moths can fly for several miles and cause new infestations.
Cultural controls, applications of Baccillus thuringiensis spp. kurstaki, and the Entrust formulation of spinosad are acceptable for use in organically grown vegetable fields. When using B. thuringiensis, apply multiple times and at close intervals to expose survivors of previous applications to another dose. When mixing, decrease the water volume to concentrate the dose ingested by the larvae, but make sure the volume applied still ensures thorough spray coverage. Targeting a specific larval stage is difficult because leafrollers have overlapping generations.
Prevention is especially important in quarantine zones. It is difficult to distinguish light brown apple moth larvae from other leafrollers, so a preventive approach, consisting of sanitation, monitoring, and early chemical treatments targeting all species of leafrollers, is currently suggested for cole crops within the quarantine zones.
Base the frequency of monitoring on the relative proximity of cole crops to high-risk areas or a history of detection. Increase monitoring frequency where an infestation is found. During the growing season through harvest:
Insecticide sprays for other lepidopteran pests such as armyworms, corn earworm or diamondback moth may control leafrollers. However, apply insecticides if leafrollers are detected while scouting to prevent infestations in harvested produce and possible quarantine issues.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|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. Not all registered pesticides are listed. Always read the label of the product being used.|
|(Success)||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.|
|(Radiant SC)||6–10 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: It is extremely important to rotate to an insecticide with a different mode of action after two successive applications. Resistance has developed where rotations between spinosad and spinetoram have been made because they have the same mode of action. Maintaining proper pH of the spray-tank water is critical for maximum efficacy.|
|C.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: To be effective must be applied no later than the second instar.|
|(Coragen)||3.5–5 fl oz||4||3|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|(Intrepid 2F)||6–12 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|(Proclaim)||3.2–4.8 oz||12||See label|
|MODE-OF-ACTION GROUP NUMBER1: 6|
|G.||METHOMYL*||0.5–1 lb||48||See label|
|MODE-OF-ACTION GROUP NUMBER1: 1A|
|MODE-OF-ACTION GROUP NUMBER1: 22|
|I.||DIAZINON*||Label rates||96 (4 days)||7|
|MODE-OF-ACTION GROUP NUMBER1: 1B|
|COMMENTS: Do not allow this insecticide to run off into surface waters.|
|‡||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 chemicals 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; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode-of-action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their website at http://www.irac-online.org/.|
UC IPM Pest Management Guidelines:
UC ANR Publication 3442
S. Joseph, UC Cooperative Extension, Monterey County (leafrollers)
S. K. Dara, UC Cooperative Extension, Santa Barbara County (leafrollers)
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgments for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside