The recommended treatment for bark scale is Ferti-Lome Tree & Shrub Systemic Insect Drench, available at Merrifield or on Amazon (suggestion: measure your tree first so you’ll know how much to order). This is a pesticide, so be sure to follow directions carefully (see below). Because it can kill bees and other pollinators, please wait until after sundown to apply since bees are no longer active at that time. It also can be toxic to pets and people so keep pets away until the ground has dried, and attend to all precautions.
- Water your tree the night before.
- Measure the circumference (distance around) each trunk at 4.5 feet above the ground. Write these numbers on a note pad and then add them together. This total is the number of ounces of drench you will need in step 5 below.
- If the total is 30 or less, clear a circular area 2 feet from the trunks, removing any sticks, debris, vines, or mulch. Push back the dirt a little to make a small wall around this area, especially on the down-hill side of any slope. If the total from step 2 is greater than 30, clear an area 3-4 feet from the trunks. TIP: Break up the top of the exposed dirt a little so the drench can soak in better.
- If the total from step 1 is less than 50, put 1 gallon of water in a bucket. If it is 50 or more, put 2 gallons of water in the bucket.
- Shake the drench container and then use a measuring cup with ounce increments to measure the number of ounces calculated in step 2 above (the Landscape Committee has a measuring cup you can borrow because you do not want to use one from your kitchen).
- Carefully pour the drench into the bucket of water and mix well.
- Slowly pour the drench around the tree trunk within the cleared area you prepared in step 3, allowing it to soak in before adding more.
- Do not let pets or children in the area until it’s dry and then cover with mulch.
- Repeat the following April.
The ferti-lome website has more information and warnings.
Also, the recommended treatment needs to be applied every year (preferably in April; so if you haven’t already treated your tree, you should do so immediately). See Fairfax County Master Gardeners for more information.