Nectria vs. Bark Beetles

What’s the Difference

• Bark beetles are small insects while Nectria is a fungus. Bark beetles are usually between 1/16 and 1/4 inch long, and are commonly black, brown or dark red. They are rarely even noticed, however. The first indication that they are in the area is usually the damage done to the trees. Nectria fungi produce little orange, red or white growths on the tree bark.

The Damage They Do

• Nectria can kill branches or even entire trees and shrubs while bark beetles rarely cause that much damage. Nectria infects trees where the bark has been damaged and kills the bark as it spreads. It causes cankers that look like a slightly sunken, discolored patch, usually where a tree or shrub has been injured or where there is a dead branch. The fungus is usually not noticed until spring when the tree or shrub may not produce leaves on all of its branches or may wilt. Bark beetles are more likely to attack weakened or diseased trees and shrubs but they can attack those that are healthy and thriving. They lay their eggs under the bark surface of tree limbs, trunks and shrub stems. The larvae feed on the inner layer of bark until they mature, then chew through the bark to emerge, usually toward the end of spring, end of summer or early in the fall. Small holes that look like the tree has been shot with buckshot are often the first and most obvious indication that they were there. Frass, a sawdust-like substance, may also be found below the holes.

Dealing With the Damage

• Remove Nectria-infected branches when conditions are dry. Disinfect the loppers or pruners between cuts with a 10 percent bleach solution. Remove branches infested with bark beetles and burn them as quickly as possible. If beetles have weakened the trunk of a tree, remove the tree for safety.

Give It a Fighting Chance

• Maintaining tree and shrub health will help prevent or at least minimize the damage from bark beetles and Nectria. Water trees and shrubs as necessary, depending on the species requirements. In general, water well-established trees when the top 3 to 4 inches of soil is dry with enough water to soak the top 1 foot of soil. Use a narrow metal rod to confirm that you applied sufficient water. Push the rod into the soil. There will be noticeable resistance where the soil is dry. Distribute the water over the entire area beneath the tree or shrub drip-line and 5 to 10 feet beyond rather than right at the trunk or base of the shrub stems. Avoid injuring trees and shrubs with lawn maintenance equipment. Giving a tree or shrub fertilizer in early spring can help to keep it growing vigorously but base the amount and type of fertilizer on the tree or shrub species requirements and soil fertility. Commonly, 12 cups of 16-4-8 fertilizer per 500 square feet of root zone is sufficient for trees and shrubs.