Description of the Pest
Omnivorous leafroller larvae are light-colored caterpillars with dark brown or black heads. When mature, they are about 0.6 inch (1.5 cm) long and have two slightly raised, oblong, whitish spots on the upper surface of each abdominal segment. Abdominal segments may have a greenish brown tinge. Larvae pupate inside a webbed shelter. Adults of the overwintering generation emerge in March. They are small, dark brown moths, 0.38 to 0.5 inch (9-12 mm) long with a dark band on the wing and a long snout. Eggs are laid in overlapping rows that resemble fish scales. The first generation of eggs usually is laid on weed hosts, and adults from this generation emerge in May or June to lay eggs in orchards on leaves and fruit. Larvae have the characteristic behavior of wriggling backward when disturbed and dropping from a silk thread attached to the leaf or fruit surface.
This pest has two to four generations per year depending on climatic conditions. Omnivorous leafrollers are more common in interior valleys and southern California mountain orchards, especially those next to vineyards, than in orchards in coastal areas or at higher elevations of the Sierra Foothills.
Omnivorous leafroller larvae often web leaves into rolled protective shelters while feeding. They feed on leaves and on the surface of fruit, sometimes webbing one or more leaves to the fruit for protection. They chew shallow holes or grooves in the fruit surface, often near the stem end. The damage is similar to that caused by orange tortrix. Larvae feed where fruit are touching, so entire clusters can be damaged.
Omnivorous leafrollers commonly develop on host plants outside the orchard and move into the orchard in early summer. Infestations often are spotty, making monitoring difficult. Throughout the season, watch for leafrollers when monitoring other pests.
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General predators such as lacewings, Phytocoris, assassin bugs, and minute pirate bugs may feed on eggs and larvae. Preservation of natural enemy populations is an important part of keeping leafroller numbers low. Use selective materials that are least disruptive of biological control when treating other pests.
Organically Acceptable Methods
Biological and cultural control along with applications of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable.
Monitoring and Treatment Decisions
Begin monitoring by placing pheromone monitoring traps in the orchard by mid-February in the San Joaquin Valley to establish the biofix for the first flight; biofix is the first night moths are consistently caught in traps over the period of several nights. First generation omnivorous leafrollers are most likely to appear on weeds or cover crop; treatments for this first brood are probably not necessary and are likely to be ineffective. From the first biofix, accumulate degree-days (DD) to estimate what the onset of the second flight will occur. Use a lower threshold of 48°F and an upper threshold of 87°F.
It takes about 1168 DD for omnivorous leafroller to develop from egg to adult. As the start of the second flight nears, be sure to have fresh trap liners and lures in place. When the second flight biofix is determined by trap catches, begin accumulating degree-days. Research in the central San Joaquin Valley indicates that the optimum single treatment timing is between 700 and 900 DD after the start of the flight. Monitor the fruit closely for signs of damage. No treatment threshold values are available.
Calculate degree days for omnivorous leafroller for your location using the omnivorous leafroller pest model or degree-day table. To learn more about using degree days to time insecticide applications, watch the degree-days video.
|Common name||Amount per acre**||REI‡||PHI‡|
|(Example trade name)||(conc.)||(dilute)||(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.|
|(Intrepid 2F)||8–16 fl oz||4||14|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|COMMENTS: Functions as a larvicide (must be ingested for it to be effective). For each generation, begin applications at early egg hatch before webbing and sheltering begin. Make a second application in 10–14 days. Spray coverage is extremely important. Ground application should use 200 gal water/acre with a sprayer speed of 1.5 mph. The addition of a spray adjuvant is recommended to enhance spray coverage.|
|(Entrust)#||2–3 oz||0.67–1 oz||4||7|
|(Success)||6–10 fl oz||2–3.3 fl oz||4||7|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: To prevent the development of resistance to this product, rotate to a material with a different mode of action after treating two consecutive generations. Do not apply more than 3 sprays per season directed at leafrollers. Do not apply more than 9 oz/acre per crop of Entrust or 29 fl oz of Success/acre per crop. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|C.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|(various products)||Label rates||4||0|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: Least harmful to beneficials. Bacillus thuringiensis is a stomach poison and must be consumed by the leafroller; therefore it is most effective when applied during warm, dry weather when larvae are actively feeding. Most effective against young larvae. Requires more than 1 treatment; apply second application 7 to 10 days after first.|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|COMMENTS: Do not apply dilute applications of more than 200 gal/acre; use 100 to 150 gal/acre for best results.|
|(Delegate WG)||4.5–7 oz||4||7|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS:Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.|
|**||For dilute application, rate is per 100 gal water to be applied in 300 to 500 gal water/acre, according to label; for concentrate applications, use 80 to 100 gal water/acre or lower if the label allows.|
|‡||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.|
|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).|