Branch and twig borer (Melalgus confertus)
Grape twig borer (Psoa quadrisignata)
Polycaon borer (Polycaon spp.)
Pest description and crop damage Cane or twig borers are problematic in vineyards situated in close proximity to riparian areas or woodlands. These insects have a wide host range but predominantly impact older vineyards where vines have large pruning cuts and/or old wood. Borers can also be found in young vineyards (<10 years of age) in western Oregon. These vineyards are often located near old orchards, abandoned vineyards and/or riparian areas. Both adults and larvae damage the vine. Larvae bore into older canes and pruning cuts where they live until they emerge as adults. Adults burrow into the base of new shoots in spring to feed. The burrowing and feeding activity can cause significant tissue damage that results in wilted and dead shoots. Severe infestation can result in crop losses and damage can be significant. Holes (~0.16 inch) can be found at the base of newly grown fruiting shoots or the base of old canes with frass or wood filings surrounding the hole. Cane-pruned vineyards appear to be more effected than spur-pruned vines.
Biology and life history Adults are long, brownish black and are visible early in the season (spring). They measure between 0.4 to 0.7 inch long. Females are slightly larger than males. Larvae live within the cane/shoot for nearly a year before they emerge the next spring.
Sampling and thresholds Monitor the vineyard using corrugated cardboard traps (see black vine weevil traps) placed at the base of the vine trunk in order to capture the pest during its active period at night. Scout vineyards for flagging or drooped shoots in spring and examine the shoot for holes and cut open the shoot to determine if there has been evidence of burrowing. No economic thresholds have been determined.
An entomopathogenic nematode, Steinernema carpocapsae, has been used for biocontrol of twig borers. A commercial preparation of the nematode must be applied to burrow holes before budbreak in order to be effective.
The best way to manage twig borers is through sanitation. Remove pruning brush from the vineyard and destroy before the borers emerge in spring (March-May). Remove and destroy any alternate hosts from fence lines or dead shrub/debris piles from the vineyard and close surrounding areas. The risk of damage by these insects is increased if the vineyard is near a poorly managed or abandoned orchard or vineyard.
Management-chemical control: HOME USE
It is difficult to control twig borers with chemical insecticides due to their burrowing nature. There is only a small window of opportunity to apply insecticides-typically in spring-when adults are mobile and have not yet laid their eggs within the shoot or cane. Do not apply chemical controls if adults are no longer visible.
- plant essential oils (cinnamon, garlic, peppermint, thyme)-Some formulations are OMRI-listed for organic use
- pyrethrins-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
It is difficult to control twig borers with chemical insecticides due to their burrowing nature. There is only a small window of opportunity to apply insecticides, typically in spring, when adults are mobile and have not yet laid their eggs within the shoot or cane. Do not apply chemical controls if adults are no longer visible.
- carbaryl (various brands) at 1 to 2 lb ai/a. PHI 7 days. REI 6 days. Avoid using if mite outbreaks are a concern. Toxic to bees; do not apply when bees are foraging. Group 1A insecticide.