Inchworms, also known as cankerworms, attack trees by feeding on their foliage. These harmful pests consume the tissue between leaves' veins, leaving behind skeletal frameworks. Their feeding ruins trees' aesthetic appearance and stops the plants from photosynthesizing, or producing food. If left untreated over time, infested trees die. With the help of multiple treatment options, each targeting a specific developmental phase of inchworms, you can eradicate inchworms from your landscape.
Things You'll Need
- Tape measure
- Cotton batting or insulation
- Scissors or utility knife
- Electrical tape
- Tar paper
- 1/4-inch-long staples
- 2 pairs of disposable rubber gloves
- Sticky adhesive
- Plastic zipper bag
- Safety glasses
- Dust mask
- Disposable tablespoon
- 1-gallon container
- Dormant horticultural oil
- Tank sprayer
- Disposable stick
- Disposable teaspoon
- Bacillus thuringiensis
- Ladder (optional)
Measure the distance around an affected tree's trunk 2 to 3 feet above ground level in fall to mid-winter. That time of year is before adult inchworms emerge from soil. Cut out a piece of cotton batting or insulation equal in length to the trunk's measurement and 6 to 12 inches wide.
Wrap the piece of cotton batting or insulation around the tree's trunk 2 to 3 feet above ground level. Tape the material's ends together with electrical tape, securing the material in a ring around the trunk.
Cut a piece of tar paper to make it equal in width to and 4 to 5 inches longer than the piece of cotton batting or insulation wrapped around the tree trunk. Wrap the tar paper around the tree trunk, placing it on top of the batting or insulation. Overlap the tar paper's ends. Staple along the edge of the tar paper's exposed end with a stapler containing 1/4-inch-long staples, securing the tar paper in a ring around the tree trunk. Staple around the top edge of the tar paper to attach it to the cotton batting or insulation and keep it from slipping downward.
Put on a pair of disposable rubber gloves. Scoop some sticky adhesive with your gloved fingers. Rub the adhesive on the surface of the tar paper. Apply additional adhesive as needed to create a 3-inch-wide sticky adhesive ring around the entire piece of tar paper. Remove your gloves, and throw them away.
Wait for the tar paper's sticky adhesive to become full with adult inchworms. Put on a pair of disposable gloves. Cut or tear the tar paper off the cotton batting or insulation. Fold the tar paper in half, and tuck it into a plastic zipper bag. Seal the bag, and discard it in a trash bin.
Attach a new piece of tar paper over the tree trunk's cotton batting or insulation in the same manner you attached the first piece of tar paper. Apply a new ring of sticky adhesive to the tar paper, repeating the procedure you used previously.
Replace the tree trunk's tar paper as needed to trap as many adult inchworms as possible in the sticky adhesive. Remove both the tar paper and cotton batting or insulation when adult inchworms stop emerging from the soil.
Dormant Horticultural Oil
Wait until late fall or early winter, when adult inchworms finish emerging from soil and die but before their eggs hatch in spring. Pour 5 tablespoons of dormant horticultural oil and 1 gallon of water in a tank sprayer to create a 2 percent solution of the oil spray. Stir the liquid thoroughly with a disposable stick.
Screw the lid on the tank sprayer, tightening it completely. Move the tank sprayer's pressurizing handle up and down until it becomes difficult to do so. That task pressurizes the tank.
Point the tank sprayer wand's nozzle at an affected tree's trunk. Press the nozzle's button to activate the spray. Move the wand up and down slowly while walking around the tree. Keep the nozzle pointed at the tree's trunk. Shake the tank sprayer up and down every 5 minutes to prevent the oil from separating from the water. Coat the entire trunk completely with the spray, ensuring that the spray comes into direct contact with all inchworm eggs.
Bacillus Thuringiensis Spray
Wait until all inchworm eggs hatch and the hatched larvae are less than 1 inch in length. Pour 4 teaspoons of Bacillus thuringiensis and 1 gallon of water into a tank sprayer. Mix the solution thoroughly with a disposable stick.
Tighten the tank sprayer's lid to secure the solution inside the tank. Pump the sprayer's pressurizing handle up and down until it becomes difficult to do so. That action pressurizes the tank.
Point the tank sprayer wand's nozzle at an affected tree's leaves. Press the nozzle's button to activate the spray. Spray the solution on the top and bottom sides of the leaves, covering all feeding inchworms with the spray. Coat each leaf surface completely with the liquid, stopping the spray just before it begins to drip from the leaves. Shake the sprayer tank every 5 minutes to keep the solution's contents from separating. Use a ladder if needed to reach the top of the tree's foliage.
Reapply the Bacillus thurnigiensis-water solution every seven days as needed until you no longer see inchworms. Coat the entire canopy during each application.
Tips & Warnings
- Mix the dormant horticultural oil at a rate of 1 percent, or 2 1/2 tablespoons per 1 gallon of water, when using the solution to spray actively growing trees or maple varieties. Otherwise, the spray could damage their growth.
- Do not apply dormant horticultural oil when the temperature drops below 40 degrees Fahrenheit or rises above 90 degrees Fahrenheit.
- Never spray dormant horticultural oil or Bacillus thurnigiensis on a windy day. Otherwise, it will drift onto other plants or into your neighbors' yards. Never spray either solution within 24 hours of rain or the rain will wash the solution from the tree and into the soil.
- Keep dormant horticultural oil and Bacillus thurnigiensis away from children and pets. Store the substances in their original containers and away from food.
- Wear protective clothing, including safety glasses, a dust mask, gloves and a hat when spraying dormant horticultural oil or Bacillus thuringiensis to prevent its direct contact with your skin. Shower thoroughly and wash your clothes after using the spray.
- Use a Bacillus thurnigiensis solution within 12 hours of mixing it.
- Read all label directions and warnings before mixing and applying any spray.
- North Carolina Cooperative Extension: Fall Cankerworm
- Ohio State University Extension: Spring and Fall Cankerworms and Other Inchworms and Loopers
- Bonide Products Inc.: All Seasons Horticultural and Dormant Spray Oil Concentrate
- Bonide Products Inc.: Bacillus Thuringiensis (BT) Thuricide Concentrate
- Photo Credit Hemera Technologies/PhotoObjects.net/Getty Images