“How do I get rid of vine weevils in the garden without using expensive nematodes?” Question from Kathy of Sparks, Nevada
Answer: The greatest damage done to vines, like hops and grapes, and shrubs, like rhododendron and hydrangea, is caused by adult black vine weevils. The adults are also the most vulnerable to treatment. The larvae do chew on the roots of host plants, but their damage is minimal unless their populations are very high. Either way, I will offer management solutions for both life stages. None will involve the use of beneficial nematodes.
Black Vine Weevil Larvae Management
Black vine weevil adults emerge in April, and the females will start laying eggs at the base of host plants around two to three weeks after emergence and continue for another two and a half months. One female can lay up to 500 eggs. The eggs hatch shortly after and the larvae feed on roots for 10 months until the following spring season.
Cultivating the soil around the base of plants in early to mid-spring can damage some larvae and pupating adults. A soluble Neem oil drench can also be helpful in managing these weevils at the larval stage. Choose an OMRI Listed product that is approved for organic gardening, if you are an organic gardener. Some also claim that applying a thick layer of diatomaceous earth at the base of infested plants can also help.
Black Vine Weevil Adult Management
The adults can be very damaging, attacking host plant flower buds and blooms as well as foliage. They chew half-circle notches in leaf edges, making their damage easy to spot. It is easiest to manage the adults when they are emerging from the soil in spring. The University of California recommends you begin by monitoring emerging populations using cardboard tree wrap traps around the base of vines or shrubs. Neem oil and pyrethrin sprays can be used to kill the adults. Spinosad sprays have also been shown to be helpful. You can also pick them off by hand to manage smaller infestations.
I hope that these tips help! to learn more, please visit the Missouri Botanical Garden’s page on black vine weevil.
Black Gold Horticulturist