How to Manage Pests

UC Pest Management Guidelines

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.

DAMAGE

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.

MANAGEMENT

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.

Biological Control
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General preators 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.

Cultural Control
Remove fruit mummies and destroy both the fruit and potential overwintering weed hosts, such as horseweed, common lambsquarters, little mallow, curly dock, and legumes, by clean cultivation.

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   Degree-day calculator    Degree-day table
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. (For assistance in calculating degree-days, see "Degree-days". 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.

Common name		Amount to use**			R.E.I.+	P.H.I.+
(trade name)		(conc.)		(dilute)	(hours)	(days)
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees Not all registered pesticides are listed. Always read label of product being used. and environmental impact.
A.	SPINOSAD
	(Entrust)#	2–3 oz		0.5–0.75 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/season directed at leafrollers. Do not apply more than 9 oz/acre/crop of Entrust or 29 fl oz of Success/acre/crop.
B.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates		—	4	0
	MODE OF ACTION GROUP NUMBER1: 11.B2
	COMMENTS: Least harmful to beneficials. Bt 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 7–10 days after first.
C.	METHOXYFENOZIDE
	(Intrepid) 2F	16 fl oz		—	4	14
	MODE OF ACTION GROUP NUMBER1: 11.B2
	COMMENTS: Functions both as an ovicide (when applied to eggs and when eggs are laid on residues) and as a larvicide (must be ingested 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.
D.	CHLORANTRANILIPROLE
	(Altacor)	3–4.5 oz	—		4	14
	MODE OF ACTION GROUP NUMBER1: 28
	COMMENTS: Do not apply dilute applications of more than 200 gal/acre; use 100–150 gal/acre for best results.
E.	SPINETORAM
	(Delegate) WG	4.5–7 oz	—		4	7
	MODE OF ACTION GROUP NUMBER1: 5
**	For dilute application, rate is per 100 gal water to be applied in 300-500 gal water/acre, according to label; for concentrate applications, use 80-100 gal water/acre or lower if the label allows.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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.
—	Not recommended or not on label.
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 Web site at http://www.irac-online.org/.

IMPORTANT LINKS

• Degree-day calculator
• Degree-day table

PUBLICATION

UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, Sutter and Yuba counties

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