Adults of the black vine weevil are 0.35-0.51 inches in length and are therefore slightly larger than some of the other destructive species of Otiorhynchus. Adults are also black in color, all are female, and they cannot fly. This insect is native to Europe and is now found in the northern half of the United States and Canada. Adults will drop from foliage to the ground when disturbed and are easily hidden due to their camouflaged coloration. Adults require a few weeks of feeding before each female will lay up to 500 eggs in the soil near the base of the plant around the end of June, early-July. These eggs will hatch and larvae will burrow into the soil to feed on the roots of the plant. Larvae are white approx. 1/2 an inch in length with brown heads, legless, and C-shaped. This weevil usually overwinters as a partially developed larvae, but occasionally adults will seek shelter, such as homes, in which to overwinter. Larvae do a lot of destructive feeding in late-May, early- June just prior to pupation. Pupae are milky-white with visible appendages. One generation per year in the Northeast. Many additional weevil species are pests of ornamental plants.
Tiny, hemispherical notches in leaf margins are a sign of adult feeding, usually on lower branches. However, other weevils will cause this type of damage on rhododendron; it can only be used diagnostically on yew, as no other insects currently cause that type of damage on that host. The major damage is caused by larvae feeding on the rootlets. This can be a very serious pest.
Monitor adults with crumpled burlap around plant base, as the adults hide in dark places during the day and are active at night. Pitfall traps around the base of infested plants may also be used. Look for notched leaves on host plants, particularly yew, starting in June. Larvae may be found on the roots of wilting host plants with notched leaves. Scouting is highly necessary in areas where this insect is an issue.
Some physical barriers to the adults (on the stem/base of the plant) have been suggested, since adults cannot fly and must crawl up the plant. Success varies. Knocking adults off the plant and onto a white surface, such as a sheet, so they are visible and can be collected and killed may be very time consuming (and must be done at night, when the adults are active). Some adults may be missed. Cleaning up beds and leaf litter/dropped branches can help remove favorable overwintering sites for the adults. Some rhododendrons are resistant to foliar damage.
Birds may be good predators of this insect. Beneficial nematode drenches are available for the larvae, and are most effective in containerized plants. Apply when larvae are present and when temperatures are favorable to the species of nematode being used. Follow instructions carefully as the nematodes are living organisms and proper treatment can increase efficacy (such as watering before/after nematode application).
Acephate (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Chlorpyrifos (N)
Clothianidin (NL)
Entomopathogenic nematodes (L)
Fenpropathrin (NL)
Gamma-cyhalothrin (L)
Imidacloprid (L)
Isaria (paecilomyces) fumosoroseus (NL)
Lambda-cyhalothrin (L)
Metarhizium anisopliae (robertii) (NL)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Tau-Fluvalinate (NL)
Adults only active at night. Spray for adults late in the day for best management. Thoroughly wet foliage and stems to runoff on Taxus and Rhododendron. Recommendations to treat at three-week intervals exist, but only according to label rates.
Active ingredients that may be applied systemically include: acephate (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), imidacloprid (soil drench), Metarhizium anisopliae (robertii) (soil drench), and neem oil (soil drench).
When used in nurseries, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
