Washington Tree Care: Diseases and Insect Infections to Watch For

Cottonwood and elm are both beautiful, fast-growing deciduous trees. The tall stately appearance of either tree can be an attractive complement to any landscape. Unfortunately, there are diseases and insects which plague these trees.

Slime Flux

This bacterial infection gets its name from the frothy slime that oozes out of the tree bark after infection. The ‘foam’ dries leaving a dry scum.
Wounds in the bark provide the source of entry. Weed eaters, improper pruning or even the family cat can break the bark. The bacteria enters the tree through these wounds.

The type of slime flux that targets the heartwood of the tree is of most concern in cottonwood and elm. In heartwood infections, the bacterial digestion of the wood creates internal pressures up to 60 lbs./sq. in. In most cases this pressure is relieved through a crack in the bark. The oozing slime is the first evidence that the bacteria is fermenting the cellulose of the tree. The bark dies as the bacteria infected slime infects it. The slime also kills any grass it comes in contact with.

The life of the tree may be extended if a certified arborist drills a hole in the infection site and inserts a pvc pipe into the tree. The pipe allows the slime to drain away from the tree even though it doesn’t cure the infection.

The bacterial flux that infects the cambium and bark layers produces a foul smelling slime. If caught early, the tree may be saved. A certified arborist can excise the infected sections. Once more than half of the tree trunk is involved, complete removal of the tree is usually the only choice.

Aphids, Scale & Mealybug

All three of these insect pests are sucking insects which feed on plant juices. They infect the new, tender growth of the tree.

Aphids like cottonwood, especially if there is a local ant population as well. The trees will start ‘dripping’ with a sap-like liquid. The best way to treat for aphids is to spray with insecticidal soap and put out ant traps that use boric acid.

Scale and mealybug are more difficult to eradicate. If regular treatments with insecticidal soap don’t clear up the infestation, it may be necessary to remove the infected portions of the tree. This is an operation best performed by a certified arborist.

Borers

There are a number of borers which are attack cottonwood and elm. Signs of an infestation include shoots that turn black, shrivel and then die. The larvae burrow into the phloem which can severely damage young or stressed trees.

Leaf Beetles

The cottonwood leaf beetle is 1/4-inch long. The beetle can completely defoliate a cottonwood tree.

The elm leaf beetle is especially prolific. If warm weather continues long enough into the fall, three generations of beetles may hatch in one year. Both adults and larvae eat the underside of the leaves. The leaves then dry up and then drop.

Consult with a certified arborist if you suspect a leaf beetle infestation. Prevention and control can save more than your tree. It can also reduce problems with beetles moving into your home for shelter in the winter.