How to Manage Pests

UC Pest Management Guidelines

Grape

Branch and Twig Borer

Scientific name: Melalgus (=Polycaon) confertus

(Reviewed 7/15)

In this Guideline:

Description of the Pest

The branch and twig borer, also known as the grape cane borer, occurs throughout California. Adult borers are dark brown beetles, cylindrical in shape with a pronotum that is wider near the head than the posterior end. Females are about 0.7 inch long; adult males are smaller, about 0.3 to 0.4 inch long. Larvae have white bodies that are typically curved in a C-shape and enlarged at the anterior end; the head is brown. Branch and twig borers have one generation per year. Adult emergence starts in March and continues through April. Larvae spend up to 10 months in tunnels they excavate.

Damage

Both adults and larvae injure grapevines. Larvae bore into wood at dead or dying parts of vines, often in old pruning scars. Adults burrow into fruiting canes at the base of the bud or shoot, or they burrow into the crotch formed by the shoot and spur. Feeding is often deep enough to completely conceal the adult in the hole. Feeding at the base of shoots on spurs will cause shoots to wilt (flagging) and fall. This pest is most serious in cane-pruned vineyards where feeding on canes can cause them to break when shoots reach a length of 10 to 12 inches, if a strong wind occurs. Shoot wilting can also be caused by Botrytis.

Management

Establishment of branch and twig borer in a vineyard may be attributed to one or two factors: (1) proximity to habitat suitable to the insect, such as riparian or woodland areas, old orchards, or unmaintained vineyards, and (2) failure to destroy or adequately remove dead or damaged parts of vines that may have resulted from disease (such as Eutypa and Pierce's disease) or cultural practices such as T-budding, lowering the vine head, or mechanical pruning.

Chemical control is normally not necessary if good cultural controls are practiced. April treatment of carbaryl for cutworms offers some measurable control of adult borers but may cause mite outbreaks later in the season.

Biological Control

The many species of general predators found under the bark of grapevines may assist in maintaining lower populations. Treatments with commercial formulations of the entomopathogenic nematode Steinernema carpocapsae, which can move through frass tubes to infect larvae, may be of some benefit.

Cultural Control

The best way to manage branch and twig borer in vineyards is to prevent invasion and establishment of the beetles through cultural methods. Wood and brush piles of any kind of tree or shrub should be completely removed from the vineyard or burned before emergence of adult beetles in March. Remove dead or dying portions of vines and destroy them with other prunings. Do not leave grapevine prunings in the vicinity of the vineyard. All prunings must be removed from berms on the vine rows and destroyed to optimize sanitation. If mechanical cane chipping or cutting is used for pruning disposal, the residue should be incorporated into the soil or composted before adult emergence. Good vine health is important for reducing sites of borer establishment in vineyards.

Organically Acceptable Methods

Biological and cultural controls are organically acceptable, including the use of beneficial nematodes.

Monitoring and Treatment Decisions

Look for shoot wilting (flagging) and drying leaves when you monitor your vineyard during the period of rapid shoot growth. In coastal regions, adults continue to emerge through April. Examine the base of these shoots for a 0.4 inch diameter hole. If no holes are present, another possibility is a Botrytis infection. Cut the shoot in half and look for brown discoloration.

After pruning, examine old pruning scars and dead parts of vines for brown frass and fine wood dust filling the holes that were made by borer larvae. Borer holes are detected more easily during the dormant season. No control action thresholds have been established. It is unlikely that borer injury in cordon-pruned vineyards would ever justify chemical treatment if good vineyard pruning and sanitation is practiced. Cane-pruned vineyards with a history of borer injury may require treatment.

Common name		Amount per acre**	R.E.I.‡	P.H.I.‡
(Example trade name)			(hours)	(days)
UPDATED: 7/15
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. Not all registered pesticides are listed. Always read the label of the product being used.
A.	CARBARYL*
	(Sevin XLR Plus)	1–2 lb	144 (6 days)	7
	MODE-OF-ACTION GROUP NUMBER1: 1A
	COMMENTS: May cause mite outbreaks; do not use where mites are a chronic problem. Extremely toxic to honey bees. To protect honey bees, apply only during late evening, night, or early morning when bees are not present. Do not spray directly nor allow drift onto blooming crops or weeds where bees are foraging.
B.	STEINERNEMA CARPOCAPSAE#	Label rates	NA	NA
	COMMENTS: Nematodes are perishable, so store them under cool, dark conditions. Use hand sprayer to aim spray at infected cordons. Most effective when applied during January and February.
**	Apply with enough water to provide complete coverage.
‡‡	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 R.E.I. exceeds the P.H.I. The longer of two intervals is the minimum time that must elapse before harvest.
*	Permit required from county agricultural commissioner for purchase or use.
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/.
#	Acceptable for use on organically grown produce.
NA	Not applicable.

IMPORTANT LINKS

• Dormant sanitation
• Photos of flagging symptoms

PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448

Insects and Mites

L. G. Varela, UC IPM Program and UC Cooperative Extension, Sonoma County
D. R. Haviland, UC IPM Program and UC Cooperative Extension, Kern County
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
F. G. Zalom, Entomology, UC Davis
L. J. Bettiga, UC Cooperative Extension, Monterey County
R. J. Smith, UC Cooperative Extension, Sonoma County
K. M. Daane, Kearney Agricultural Research Center, Parlier

Acknowledgment for contributions to Insects and Mites:

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