How to Manage Pests

UC Pest Management Guidelines

Plum

Omnivorous Leafroller

Scientific name: Platynota stultana

(Reviewed 5/06, updated 4/09)

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

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.

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 (PDF).

Common name		Amount to Use**		R.E.I.+	P.H.I.+
(trade name)		(conc.)	(dilute)	(hours)	(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. Not all registered pesticides are listed. Always read label of product being used.
A.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates		4	0
	MODE OF ACTION GROUP NUMBER1: 11.B2
	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	4	7
	(Success)	6–8 oz	1.5–2 oz	4	7
	MODE OF ACTION GROUP NUMBER1: 5
	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	4	7
	MODE OF ACTION GROUP NUMBER1: 18A
	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.
+	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.
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
• Final fruit damage evaluation form for codling moth, caterpillars, scale, and ripe fruit rot (PDF)
•  Using degree-days to time insecticide applications

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 Insects and Mites:

• R. E. Rice, Kearney Agricultural Center, Parlier

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