Our flowering cherry tree is 10 years old and within the past four years has become infected with something that is causing the lower branches to wither and the tree to drop a sticky sap.
I've tried researching but have found nothing that matches the weird little growths that are on the branches.
The top of the tree appears healthy and it still blooms. Can you tell me what this is and how to treat it?
Rona Knapp, Folsom
According to UC Master Gardener Maureen Hefti, your cherry tree is infested with scale insects. The photos you supplied are a bit blurry, but based on the color of the insects, they may be either Kuno scale or European fruit lecanium. Both are soft-bodied scale species, and both feed on cherry trees.
Soft-bodied scale insects firmly attach to tender, woody tissue and use their piercing mouthparts to suck sugary juices found in plant tissues. They excrete honeydew, a sugary substance that ants find irresistible.
Ants will climb trees and protect scale from natural predators literally farming a colony of scale in exchange for easy food.
One method of reducing scale numbers is to exclude ants. This way, the natural predators will have access to the scale.
Place a band of sticky material such as Tanglefoot on thin cardboard around the base of your cherry tree, about 6 inches off the ground. Make sure there are no routes for ants under the band. Also eliminate other routes ants may use to reach scale by pruning branches away from fencing, buildings or neighboring trees.
Another method of eliminating soft-bodied scale is to spray a hard stream of water on infested branches. The soft bodies of the scale break apart under water pressure.
Applications of supreme or superior type horticultural oils may improve control of scale insects. Use of dormant oils is not recommended. Follow all manufacturer instructions when using any pest control product.
Use of insecticide sprays is not recommended for soft scale, as insecticides are not effective in controlling scale. Instead, they eliminate the most effective controls for scale natural predators.
Natural predators of soft-bodied scale include ladybeetles (also called lady bugs) and predatory wasps.
If you look closely at the scale, you may see a few bodies with a small hole on the outside and a hollow appearance on the inside. A predatory wasp has inserted an egg into the body of the scale, and an immature wasp has emerged from the hollow body. For bug watchers, it's pretty exciting. It's also good news for your cherry tree.
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