How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Omnivorous leafroller is a pest of plums primarily in the San Joaquin Valley. It occurs in the Sacramento Valley but seldom causes damage. Omnivorous leafrollers overwinter as immature larvae in mummy fruit and do not enter dormancy. Larvae are light colored 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. They pupate inside a webbed shelter.

Adults of the overwintering generation emerge in March. They are small, dark brown moths, 0.375 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 that hatch from this generation of eggs can cause significant damage in stone fruits. All have the characteristic behavior of wriggling backward when disturbed and dropping from a silk thread attached to the leaf or fruit surface.

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.

Primary damage results from fruit feeding. Young fruit may be destroyed, and scars on older fruit will cause them to be culled or downgraded at harvest. Feeding injury also may increase the incidence of brown rot and other fruit decays.

MANAGEMENT

Omnivorous leafrollers do not usually appear in plum trees until early summer. Regular monitoring each season is important so that prompt action can be taken if damaging populations develop. Throughout the season, watch for the presence of leafrollers while monitoring.

Biological Control
A number of parasites, including species of Macrocentrus, Cotesia (Apanteles), and Exochus, attack omnivorous leafroller larvae. General predators such as green lacewings, Phytocoris bugs, 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, legumes, by clean cultivation.

Organically Acceptable Methods
Biological and cultural control along with applications of Bacillus thuringiensis are organically acceptable tools.

Monitoring and Treatment Decisions   Degree-days calculator    Degree-days table
Begin monitoring by placing pheromone monitoring traps (see PHEROMONE TRAPS) in the orchard during bloom (by February 20) in the San Joaquin Valley and check twice weekly to establish the biofix for the first flight; biofix is the first night moths are consistently caught in traps. First generation omnivorous leafrollers are most likely on weeds or cover crops; treatments for this first brood are probably not necessary and are likely ineffective for all but the earliest varieties. From the first biofix, accumulate degree-days (DD) to estimate when 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 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 degree-days after the start of the flight. Monitor the fruit closely for signs of damage. No treatment threshold values are available.

Take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program. See FRUIT EVALUATION AT HARVEST. Record results on a monitoring form (100KB, PDF).

Common name		Amount to Use**		P.H.I.+
(trade name)		(conc.)	(dilute)	(days)
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, impact on natural enemies and honey bees, and impact of the timing on beneficials. When choosing a pesticide, also consider information relating to environmental impact.
A.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates		0
	MODE OF ACTION: A microbial (Group 11.B2)1 insecticide.
	COMMENTS: Must be applied when worms are small, before they have taken up shelter in rolled leaves. Does not destroy natural enemies. When using short-residual materials like Bacillus thuringiensis, two applications may be necessary for adequate control, one at 700 and one at 900 degree-days. Late season fruit varieties, which may be exposed to a third generation, may require additional treatments. However, considerable overlap in generations occurs by then so treatments may be needed earlier than 700 degree-days.
B.	SPINOSAD
	(Entrust)#	1.71–2.5 oz	0.43–0.6 oz	7
	(Success)	6–8 oz	1.5–2 oz	7
	MODE OF ACTION: A microbial (Group 5)1 insecticide.
	COMMENTS: Make one application about 900 DD after the start of the flight. This product is toxic to bees for 3 hours following treatment; apply in the late evening after bees have stopped foraging. Do not apply more than 29 oz/acre/year of Success or 9 oz/acre/year of Entrust.
C.	METHOXYFENOZIDE
	(Intrepid) 2F	8–16 oz	2–4 oz	7
	MODE OF ACTION: An insect growth regulator (Group 18)1 insecticide.
	COMMENTS: Use allowed under a supplemental label. Do not apply more than 16 fl oz/acre/application or 64 fl oz/acre/season.
	**  For dilute applications, 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. + Preharvest interval. Do not apply within this many days of harvest. # Acceptable for use on organically grown produce. 1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

PUBLICATION

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier

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