Weevils

Question: Hi! Based on the leaf patterns, I have two potted shrubs with root weevils. I planned to get them in the ground this Fall and I wonder if I shouldn’t plant them or if it’s OK. Thanks for any insights!

responder: Patricia Patterson Replied September 25, 2024, 11:29 PM EDT
response: You are correct. Black Vine Weevils. The adults notch the leaves, the larvae feed on the roots. The following information is from The Missouri Botanical Garden. The black vine weevil, Otiorhynchus sulcatus, also known as the taxus weevil, feeds on a wide range of ornamental plants but is most destructive in its larval stage to yew, hemlock, rhododendron, and several other broad-leaved evergreens as well as to some greenhouse plants such as asters, cyclamens, and impatiens. As an adult, it has a wide host range to include both deciduous and herbaceous plants. It is the most devastating of the root weevils throughout the northern half of the U.S. and Canada. Symptoms and Diagnosis Adult black vine weevil injury on broad-leaved evergreens and other hosts consists of marginal notching of the leaves. To detect weevil infestations on yew, examine the center of the plant near the main stems for notched and cut-off leaves. This damage is the result of adults feeding at night. The adult is 3/8 to 1/2 inches long, shiny, black, female, and cannot fly. It feeds only at night, and when disturbed, drops to the ground where it is virtually undetectable due to its coloration. Adult feeding rarely causes serious plant injury, however, the characteristic notches provide evidence that the pest is present and action is necessary to mitigate damage by the larva of the next generation. The larva causes the most damage by feeding on the roots and girdling the lower stems, disrupting the flow of nutrients and water through the plant. Its feeding may result in the death of the plant. The larvae are legless, C-shaped, and white with reddish-brown heads. They may be found at a depth of from 3/4 to 16 inches in the soil around the roots. Pupation occurs in the soil near the surface. Pupae are white with very prominent legs and antennae. Life Cycle Partially grown larvae overwinter in the soil. Adults emerge from the soil in late spring and egg-laying begins one to two weeks later. The female lays up to 500 eggs in the soil near the base of the plant over a period of two to three weeks. Larval feeding takes place from midsummer, when the eggs hatch, continues into the fall, and then again in the spring. Occasionally adults overwinter, which complicates the life cycle because eggs are laid earlier. There is usually one generation per year. The most vulnerable stage is the adult. The larvae are much less vulnerable because they are protected by the soil. Integrated Pest Management Strategies 1. Nematodes can be applied as a soil drench to control larval stages of black vine weevil. Several species have been reported to be effective. The nematodes kill by entering the victim's body and reproducing. Two species are commercially available: Steinernema carpocapsae and Heterorhabditis heliothidis. H. heliothidis has been shown to be more effective against the early stages of the weevil at greater soil depths than S. carpocapsae. Nematodes can last three months in the soil, but soil temperature must be above 50 degrees F and the soil must be kept moist for nematode survival. Unfortunately, drenches are less effective under field conditions than in a greenhouse situation. Organic Strategies  Consult the Organic Materials Review Institute (OMRI™) for appropriate Neem products. Updated 7/2024

responder: The Question Asker Replied September 28, 2024, 2:25 PM EDT
response: Thank you so much for all of this information. Just to clarify, should I treat the plants before planting them in the earth? Thanks! With care & gratitude,Meghan Schardt  Pronouns: she/they (what's this?)Certified Clinical Herbalist / Flower Essence PractitionerDeath Care Worker / Herbal Educatorwww.redfawkesapothecary.com www.fireweedherbalism.com On Wed, Sep 25, 2024 at 8:29 PM Ask Extension <<personal data hidden>> wrote:

responder: Patricia Patterson Replied September 30, 2024, 1:47 PM EDT
response: Yes. Do note the temp. requirements for effectiveness. Good luck with the plants.

responder: The Question Asker Replied September 30, 2024, 6:56 PM EDT
response: Thank you so much for your wishes!  On Mon, Sep 30, 2024 at 10:47 AM Ask Extension <<personal data hidden>> wrote:

responder: Patricia Patterson Replied October 03, 2024, 10:10 PM EDT
response: You are welcome!