Plant Problems in May

Tree dieback in birch due to bronze birch borer. Photo by Wendy Hanson Mazet, UNCE.
Tree dieback in birch due to bronze birch borer. Photo by Wendy Hanson Mazet, UNCE.

Plant fever is in the air. Nurseries are busy. Weekends reverberate with the sound of mowers, weed eaters, blowers and power tools. People are planting, pruning, fertilizing and weeding.

Gardeners are seeing signs of insects, diseases and other plant problems. Aphids are evident on roses, ash trees, dogwoods, flowering plums, fruit trees and other plants. While you might not notice the insects themselves, you can’t miss the sticky gooey sap dripping off trees or making leaf surfaces shiny. You can’t miss the curled leaves with critters inside. Spraying plants off with a strong blast of water can help, except when the leaves are curled up. Curled leaves can be pruned out. Or, use insecticidal soap or horticulture oil to manage these pests.

You may see needle burn on pines and other evergreens. In most cases, the cause is winter injury. While the needles may be dead, the buds and twigs are usually still alive. Wait to see what happens with new growth before deciding a plant is a goner. Take good care of the trees with proper water and fertilizer. On junipers, you may see dead branches mixed in with live ones. The culprits are often voles, or meadow mice. Overwinter they gnawed off the bark of the branches and trunks. When you cut the dead branches out, you may see teeth marks. Prune out the dead branches and contact me for vole control tactics.

On apples, pears, hawthorns and crabapples, you may see the signs of fire blight, a bacterial disease. You may see leaves, stems and bark that looks like it was burned. You may see a “shepherd’s crook” effect where the leaves and small stems arch and turn downward. There may be sunken areas on the bark or wilted leaves at blossom spurs. University of Nevada Cooperative Extension has a fact sheet on fire blight.

Birch trees are starting to show whether they suffer from an infestation of bronze birch borer. When tops die out, or limbs die, you can usually find D-shaped holes on the trunk or branches. These are caused by beetles that bore into and out of a tree, damaging its vascular system. Lots of water all year can help prevent drought stress and reduce borer populations. There are also some insecticides that can help trees that are already infested.

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