Weevils on Arborvitae in Florida

Cypress Weevils

• Cypress weevils (Eudociminus mannerheimii) attack arborvitaes throughout Florida. Tan or gray scales cover the bark-consuming adults, light-spotted black beetles measuring up to 2/3 inch long. Females deposit eggs in the root and trunk recesses of damaged, weak or fallen trees, where their 1-inch, creamy-white larvae invade the tissues responsible for transporting water and soil nutrients. Limited research into the weevils' habits indicates that the adults feed and lay eggs from spring to fall and that -- in Florida -- two or more generations of grubs feed in fall and winter.

Life Cycle

• The adult pests' feeding often kills arborvitae seedlings or twigs. Larvae-infested seedlings sometimes have swollen, sap-oozing stem tissue. Peeling the bark from these stems exposes sawdust- and waste-filled larval tunnels. According to University of Florida IFAS, one northern Florida Nursery reported spiral cypress-weevil tunnels in the stems of young bald cypresses (Taxodium distichum), which grow in USDA zones 5 through 10.

Prevention

• Vigorous arborvitaes don’t attract adult cypress weevils. To keep yours healthy, plant them in full sun or partial shade and fertile, moist, sandy or loamy soil, with weekly water in dry periods during their first year. Fertilizing also boosts their vigor, but only if a soil test indicates your soil is nutrient-deficient. If so, feed the plants in spring or fall with 2 to 4 pounds of granular, herbicide-free lawn fertilizer for each 100 square feet of root zone. Scatter it evenly from within a few inches of the trunk to 18 inches beyond the branches' tips the branch tips and water it into the soil. Fertilizing is optional for arborvitaes 5 years old or older.

Weevil Control

• University of Florida IFAS Extension suggests controlling cypress weevils with commercially available nematodes and the insecticides to treat weevils are not available to homeowners. These microscopic worms burrow into and fill the root-feeding larvae with deadly bacteria. After multiplying inside the dead grubs, they migrate to living ones. Apply the treatment when sun won't damage the UV-sensitive nematodes. Pour the container's contents into 2 quarts, or the manufacturer's recommended amount, of clean tap water. Add the stirred solution to a watering can or sprayer with enough additional water to cover the area around your infested arborvitaes. Water the soil well and wet it evenly with the nematode mixture, shaking the solution frequently so the nematodes remain suspended. When you’re finished, water again. Don't worry about over-watering; the nematodes require water to swim to the infested roots. Only professionals can buy insecticides for tree-boring insects, so these are not an option.