How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Small peach twig borer larvae are almost white with a distinct black head. As larvae mature they become chocolate brown with alternating dark and light bands around the abdomen. The light, intersegmental membranes contrasted with the brown body distinguishes peach twig borer from other larvae found in stone fruits. Mature larvae are about 0.5 inch long.

Pupae are 0.25 to 0.4 inch long, brown in color and lack a cocoon. Pupation takes place in protected places on the tree and occasionally in the stem cavity of infested fruit.

Adult peach twig borer moths are 0.3 to 0.4 inch long with steel gray, mottled forewings. The long, narrow forewings are lightly fringed; the lighter gray hindwings are more heavily fringed. Prominent palpi on the head give the appearance of a snout. The bluntly oval eggs are yellowish to orange and are laid on twigs, leaves, or on the fruit surface.

Peach twig borer overwinters on the tree as a first- or second-instar larva within a tiny cell, called a hibernaculum, that is located in crotches of 1- to 3-year-old wood, in pruning wounds, or in deep cracks in bark. The overwintering site is marked by a chimney of frass and is especially noticeable when first constructed or before winter rains set in. Larvae emerge in early spring, usually just before and during bloom, and migrate up twigs and branches where they attack newly emerged leaves, blossoms, and shoots. As shoots elongate, larvae mine the inside, causing the terminals to die back. Dead shoots are known as shoot strikes or flags.

Adults from the overwintered generation usually begin emerging in April or early May. First generation larvae usually develop in twigs during May and June and give rise to the next flight of moths in late June or early July. Larvae from this and subsequent generations may attack either twigs or fruit depending on fruit maturity and population density.

DAMAGE

Peach twig borer can damage stone fruits by feeding in shoots and causing shoot strikes, or by feeding directly on the fruit. Shoot damage is most severe on the vigorous growth of young, developing trees because feeding kills the terminal growth and can result in undesirable lateral branching. As fruit matures, it becomes highly susceptible to attack; damage is most likely to occur from color break to harvest. Twig borer larvae generally enter fruit at the stem end or along the suture and usually feed just under the skin.

MANAGEMENT
   Degree-day calculator    Degree-day table
Within an IPM program, the preferred management strategy for peach twig borer is well-timed treatments of environmentally sound insecticides around bloom time. These include Bacillus thuringiensis, spinosad (Entrust, Success), methoxyfenozide (Intrepid), and diflubenzuron (Dimilin). Bloom time applications integrate well with brown rot treatment, thus helping to cut application costs. Bloom sprays are preferred over in-season sprays in an IPM program because they have less adverse impact on beneficials and nontarget organisms.

Alternatively, peach twig borer can be controlled with a spray in the delayed dormant season to kill overwintering larvae in the hibernacula. Organophosphates and pyrethroid insecticides have traditionally been used but these should be avoided because they pose surface water quality concerns and may pose some risks to raptors, aquatic invertebrates, beneficials, and other nontarget organisms. Dormant sprays of oil plus spinetoram (Delegate) spinosad (Entrust, Success) or diflubenzuron (Dimilin) do not present these environmental problems. Dormant sprays of oil alone or oil combined with an insecticide, however, have the advantage of controlling some other stone fruit pests, especially mites and San Jose scale. (Oil alone does not control peach twig borer.) Mating disruption during the growing season can also be used to supplement dormant sprays.

Mating Disruption. Mating disruption with sex pheromones can be used to supplement dormant or bloom time sprays. The main practical use for mating disruption is postbloom treatment in organic systems where other materials are not available. Mating disruption has not been reliable against peach twig borer when used alone. It is most effective in orchards with low moth populations that are not close to other untreated peach twig borer hosts or almond orchards. Efficacy is reduced by small orchard size, uneven terrain, reduced pheromone application rates, applying too low in the tree, improper timing, and high insect pressure. Follow timing guidelines given in the treatment table below.

Biological Control
Peach twig borer has about 30 species of natural enemies. The gray field ant, Formica aerata, preys on peach twig borer during spring and summer. In some years these natural enemies destroy a significant portion of larvae, but by themselves they generally do not reduce twig borer populations below economically damaging levels. Other commonly found natural enemies in California are the chalcid wasps, Copidosoma (=Paralitomastix) varicornis and Hyperteles lividus, the braconid wasp Macrocentrus ancylivorus, and the grain or itch mite, Pyemotes ventricosus.

Organically Acceptable Method
Bloom time Bacillus thuringiensis sprays, sprays of the Entrust formulation of spinosad, and mating disruption are organically acceptable methods for peach twig borer management.

Monitoring and Treatment Decisions
Bloom. Monitor for peach twig borer larvae and its damage during bloom (see EARLY SEASON MONITORING) when shoots are emerging, to determine if the pest is active. When emerging shoots are about 1 inch long, look for wilted leaf shoots and feeding at the base of flowers.

If larvae or their damage are observed at this time, a single treatment of diflubenzuron (Dimilin), spinetoram (Delegate), spinosad (Entrust, Success), methoxyfenozide (Intrepid), or chorantraniliprole (Altacor) can be applied or two sprays of Bt.

Shoot strike monitoring. Monitor all orchards from bloom onward for shoot strikes at the end of each generation. Shoot strikes first appear when the degree-day accumulation from moths in traps approaches 400 DD but more will be evident around 700-800 DD. Treatment threshold is three strikes per tree. See SHOOT STRIKE MONITORING for additional information.

Pheromone traps and degree-day accumulation. Install pheromone traps in orchards by March 20 (see PHEROMONE TRAPS). If in-season sprays are necessary (as determined by the shoot strike sample in the previous generation), you will need results from trap catches and degree-day accumulations to time them. Once the first moth has been trapped, begin accumulating degree-days (DD) using a lower threshold of 50°F and an upper threshold of 88°F. (For assistance in calculating degree-days, see "Degree-days ".)

Research has shown that best control can be achieved when treatments are applied about 400 DD from the beginning of the flight if the fruit is still green; if fruit has begun to color, however, treat at 300 DD. If Bacillus thuringiensis is used, two sprays should be applied: one at 300-350 DD and the other at 450-500 DD. If Intrepid, Altacor, or Belt is used, a single application is effective and should be applied at 300 DD.

Fruit samples. Examine fruit on trees every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and 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 (115 KB, PDF) for harvest sample.

Common name		Amount/Acre**		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.
DELAYED DORMANT
A.	NARROW RANGE OIL
	(440 or higher)	4–6 gal	1–1.5 gal	4	0
	MODE OF ACTION: Contact including smothering and barrier effects.
	COMMENTS: Choose a narrow range oil with a 50% distillation point of 440 or higher for dormant season use.
	. . . PLUS . . .
	SPINETORAM
	(Delegate) WG	3 oz	0.75 oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
	. . . or . . .
	SPINOSAD
	(Entrust)#	1.25-2.5 oz	0.3-0.6 oz	4	1
	(Success)	4–8 oz	1–2 oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
	COMMENTS: Apply with a narrow range oil to suppress overwintering mite and scale populations. For organic produce, check with your certifier to determine which narrow range oils are organically acceptable.
	. . . or . . .
	DIFLUBENZURON*
	(Dimilin) 2L	12–16 oz	3–4 oz	12	0
	MODE OF ACTION GROUP NUMBER1: 15
	COMMENTS: Apply in sufficient water to ensure good coverage. Apply with narrow range oil at 1.5% oil by volume.
	. . . or . . .
	METHOXYFENOZIDE
	(Intrepid) 2F	8–16 oz	2–4 oz	4	7
	MODE OF ACTION GROUP NUMBER1: 18
	COMMENTS: Do not apply more than 16 fl oz/acre/application or 64 fl oz/acre/season.
	. . . or . . .
	ESFENVALERATE*
	(Asana XL)	Label rates		12	14
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: An alternative to diazinon if resistance is suspected. Use when populations of peach twig borer are high. Use of this material during the dormant season may be detrimental to natural enemies of mites and result in mite outbreaks during the growing season.
	. . . or . . .
	PERMETHRIN*
	(Ambush, Pounce)	Label rates		12	14
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: An alternative to diazinon if resistance is suspected. Use when populations of peach twig borer are high. Use of this material during the dormant season may be detrimental to natural enemies of mites and result in mite outbreaks during the growing season.
BLOOM
A.	DIFLUBENZURON*
	(Dimilin) 2L	12–16 oz	3–4 oz	12	0
	MODE OF ACTION GROUP NUMBER1: 15
	COMMENTS: Include vegetable oil at the rate of 1 qt/acre. Do not apply after petal fall. Do not exceed 2 applications in any given season.
B.	SPINETORAM
	(Delegate) WG	4.5–7 oz	1.125–1.75 oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
	COMMENTS: This product is toxic to bees for 3 hours following treatment; apply in late evening after bees have stopped foraging.
C.	METHOXYFENOZIDE
	(Intrepid) 2F	8–16 oz	2–4 oz	4	7
	MODE OF ACTION GROUP NUMBER1: 18
	COMMENTS: Apply at petal fall. Do not apply more than 16 fl oz/acre/application or 64 fl oz/acre/season.
D.	SPINOSAD
	(Entrust)#	1.25–2.5 oz	0.3–0.6 oz	4	1
	(Success)	6–8 fl oz	1.5–2 fl oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
	COMMENTS: Do not apply more than 29 oz/acre/year of Success or 9 oz/acre/year of Entrust. Most effective when applied at petal fall. This product is toxic to bees for 3 hours following treatment; apply in late evening after bees have stopped foraging.
E.	CHLORANTRANILIPROLE
	(Altacor)	3–4.5 oz	0.75–1.125 oz	4	10
	MODE OF ACTION GROUP NUMBER1: 28
	COMMENTS: Do not used more than 4.5 fl oz/acre/application or more than 9 fl oz/acre/season.
F.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates	—	4	0
	MODE OF ACTION GROUP NUMBER1: 11
	COMMENTS: Treatments are timed by examining larval emergence from hibernacula. Treat when larval activity is detected by bud feeding or emergence from hibernacula and again 7-10 days later. This usually coincides with an application at the beginning of bloom and the second 7–10 days later, often full bloom to petal fall. In years when peach twig borer emergence is extended, make the second at petal fall. Compatible with fungicide sprays and can be tank mixed with them. Good coverage is essential. Ground application using a concentrate rate (80–100 gal water maximum) is preferred. If aerial applications must be made because conditions do not permit ground application, a concentrate rate (5 gal or less) is preferred. Fly material on at a height of about 20 ft over the canopy using appropriate nozzles to allow better deposition on the treetops. Precede this treatment with an oil spray during the delayed dormant season to control San Jose scale and European red mite eggs.
POSTBLOOM
A.	SPINETORAM
	(Delegate) WG	4.5–7 oz	1.125–1.75 oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
B.	CHLORANTRANILIPROLE
	(Altacor)	3–4.5 oz	0.75–1.125 oz	4	10
	MODE OF ACTION GROUP NUMBER1: 28
	COMMENTS: Do not used more than 4.5 fl oz/acre/application or more than 9 fl oz/acre/season.
C.	FLUBENDIAMIDE
	(Belt) SC	3–4 oz	0.75–1 oz	12	7
	MODE OF ACTION GROUP NUMBER1: 28
	COMMENTS: Do not used more than 4 fl oz/acre/application or more than 12 fl oz/acre/season. This product is reported to be highly toxic to bee brood.
D.	METHOXYFENOZIDE
	(Intrepid) 2F	8–16 oz	2–4 oz	4	7
	MODE OF ACTION GROUP NUMBER1: 18
	COMMENTS: Do not apply more than 16 fl oz/acre/application or 64 fl oz/acre/season.
E.	SPINOSAD
	(Entrust)#	1.71–2.5 oz	0.43–0.6 oz	4	1
	(Success)	6–8 oz	1.5–2 oz	4	1
	MODE OF ACTION GROUP NUMBER1: 5
	COMMENTS: Do not apply more than 29 oz/acre/year of Success or 9 oz/acre/year of Entrust. Most effective when applied at petal fall.
F.	PHOSMET
	(Imidan) 70 WP	4.25 lb	1 lb	5 days	14
	MODE OF ACTION GROUP NUMBER1: 1B
G.	ESFENVALERATE*
	(Asana XL)	4–6 oz	1.5–2 oz	12	14
	MODE OF ACTION GROUP NUMBER1: 3
	COMMENTS: Use is not generally recommended on perennial crops in the San Joaquin Valley because high label rates can cause outbreaks of secondary pests. While low label rates reduce the potential for secondary outbreaks in the Sacramento Valley, they should only be used where resistance to organophosphates has not become a problem and other methods such as mating disruption are not feasible.
H.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates	—	4	0
	MODE OF ACTION GROUP NUMBER1: 11
	COMMENTS: Make two applications: one at 300-350 DD from biofix and the other at 450-500 DD. Compatible with fungicide sprays and can be tank mixed with them. Good coverage is essential. Ground application using a concentrate rate (80–100 gal water maximum) is preferred.
I.	MATING DISRUPTANTS#
	(CheckMate PTB)	Label rates		0	0
	(CheckMate SF)	150-200 dispensers/acre		0	0
	COMMENTS: Mating disruptants have not provided reliable control when used alone. Used primarily in organic orchards to supplement bloom sprays. Place pheromone dispensers in orchards when you begin to catch the first moths in pheromone traps usually in April to May, depending on your location in the state. Apply in top one-third of canopy. Follow the manufacturer's recommendations for placement, the number of dispensers to use, and replacement intervals. Reapply the pheromones at the recommended timing for later varieties. If you are catching more than 5 moths per pheromone trap per week within one generation of harvest, however, treat with an insecticide rather than replacing dispensers. When using mating disruption, monitor the orchard regularly for shoots strikes at the end of each generation to verify that the technique is effective. Also monitor fruit from the tops of trees regularly for signs of larvae or damage; monitor more frequently during the final 4 weeks before harvest. Treat with insecticide if there are more than an average of 3 to 5 shoot strikes per tree after the first moth flight or if larvae are found in green fruit.
**	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 label allows.
*	Permit required from county agricultural commissioner for purchase or use.
+	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
• Fruit sampling for pest damage in harvest (115 KB, PDF)

PUBLICATION

UC IPM Pest Management Guidelines: Nectarine
UC ANR Publication 3451
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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