Its waxy evergreen leaves and sweetly scented, creamy white blooms make gardenias a stunning shrub for gardens in U.S. Department of Agriculture plant hardiness zones 8 through 10. Although cutworms aren't common pests of these evergreen shrubs, they will still feed on the gardenia if given the chance. Cutworms are typically won’t threaten the life of the gardenia plant and can be controlled with various methods.
Cutworms measure about 1 to 2 inches and are the larval stage of various species of moths. These annoying, hairless caterpillars are dull-colored, allowing them to easily blend with the soil, and will curl into a C shape when disturbed. The adult stage of cutworms are night-flying moths with a wingspan measuring between 1 1/2 to 3 inches. Cutworms feed on gardenia stems located near soil level and chew holes in foliage and flowers. Most cutworm species overwinter under plant debris or in the soil, and begin feeding during early spring. Their feeding and growing continues until the summer when the cutworms pupate in the soil and emerge as moths several weeks later.
Manually removing cutworms off the gardenia plant is a safe and effective method to controlling these annoying worms. According to the University of California, cutworms are present only in the spring, so it is vital to regularly monitor your gardenias during this period. The University of Minnesota suggests checking gardenias during the late afternoon and evening hours when cutworms are most active. When you find a cutworm, immediately pick off it off and place it in a bucket filled with soapy water.
Controlling cutworms with organic methods can be accomplished with Bacillus thuringiensis (Bt), a microbial insecticide safe for use around people, pets, beneficial insects and wildlife. Bt is essentially a stomach poison that targets cutworms, tent caterpillars, webworms and other larval stages of various insects. Once consumed, Bt kicks into action and causes the targeted pest to stop feeding. After a few days, the pest dies from starvation. Typically, a solution of 2 teaspoon of Bt mixed with 1/2 gallon of water will effectively control cutworms. However, thorough coverage with the solution is required to control cutworms on gardenias.
Pesticides containing the active ingredient carbaryl will control cutworms attacking gardenia plants. Concentrate carbaryl insecticides must be diluted in water using a rate of 2 teaspoons of the pesticide for every gallon of water. This amount will typically treat a 500-square-foot area. For easier application, mix the solution in a pump spray and thoroughly treat the gardenia including the top and underside of leaves. Follow the directions located on the carbaryl label, since each brand and type of insecticide is different.
- University of Florida Cooperative Extension Service: Gardenia Jasminoides
- University of California Statewide Integrated Pest Management Program: Cutworms
- The University of New Hampshire Cooperative Extension: Cutworms
- University of Minnesota Extension: Cutworms in Home Gardens
- Bonide: Bacillus Thuringiensis
- University of Minnesota Department of Entomology: Sevin SL Carbaryl Insecticide Label
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