BLACK VINE WEEVIL

Black vine weevil was brought to the US on European nursery stock back in the mid-1800’s. This leaf-feeding insect is well established now throughout the Flint, MI area wherever yews are used as a landscape plant. These small insects are rarely seen because they are nocturnal feeders, but the crescent-shaped gouges left in the shrub leaves they feed on can easily be found. Black vine weevil feeding damage on yew shrubs is sometimes hard to find as the dense foliage obscures the notches, but on rhododendrons, holly shrubs, Japanese pieris, and euonymus it is usually pretty easy to spot. 

Although it is the notches that black vine weevils create that attract our attention, it’s the larval damage to the roots of plants that should be of most concern. Adult black vine weevils emerge in the Flint area in May and June and feed until fall.  The grubs, which are the larval form of black vine weevil, feed on shrub roots and stems until the ground temperatures force them deeper into the soil to hibernate. 

Homeowners can take some simple steps to reduce black vine weevil grub survival. Keep landscape mulch from becoming too deep and don’t overwater your shrubs - especially in July and August when the newly hatched grubs are most active. High soil moisture and over mulching can lead to grub feeding on the stems of susceptible plants, and girdled stems lead to extremely stressed or dead shrubs. 

Spraying susceptible shrub species, starting in the early summer, is effective at controlling adult black vine weevil insects and limiting the amount of foliar damage to your shrubs. In the Flint area we start spraying for black vine weevil adults in June and recommend follow up treatments in July and August.

The most common plants attacked by black vine weevil are yew shrubs, rhododendron, holly shrubs, Japanese pieris, or euonymus. If you have these shrub species in your landscape you may want to have your plants checked for black vine weevil feeding damage.