What Is Wrong With My Fremont Cottonwood?

Are there any entrance holes with brown boring dust around them?

Are there any perfectly round, small entry-holes in trunks and primary branches?

Are the leaves small, discolored, and drop early, clusters of honey-colored mushrooms may sprout at the base of the plant?

Are there any small, black angular spots or large, irregular brown spots on foliage?

Are the leaves covered with white powder?

Are there any irregular galls on undersides of leaves, leaf stalks, and/or new shoots?

Poplar and willow borer (Cryptorhynchus lapathi) chew bark and lay eggs on current-year green shoots. Larvae chew mines 1-3 inches long beneath and in bark and wood. Fine brown boring dust can be seen around the entrances to these galleries. Some dieback may occur. Prune and dispose of infested or dying limbs or trees. Persistent insecticide treatments may be necessary to control heavy infestations.

Polyphagous shot hole borer bores perfectly round, small entry-holes into trunks and primary branches. It then creates galleries in the wood where it lays its eggs and grows the Fusarium fungus. Most heavily infested or isolated host trees need to be removed entirely or pruned (if the infestation is confined to a few branches). Chemical treatment requires a bark spray for the beetles combined with soil injection of a fungicide.

Armillaria root rot is a fungal disease that cannot be effectively controlled once it has become established. Diseased or dead plants should be uprooted and removed. Planting resistant rootstocks is the most effective method of preventing the disease.

Bacterial blight (caused by Pseudomonas syringae) Causes small, black angular spots or large, irregular brown spots on foliage. Branch cankers and brown streaks in the wood may also occur. The spread of the disease is greatest during humid, wet weather conditions. Practice good garden hygiene at the end of the season and discard, do not compost, possibly diseased plants and plant parts. Pull out and destroy infected plants.

White, powdery patches on the leaves are caused by a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining them and any surrounding plants. Water plants from below to keep foliage dry. Any affected leaves should be cut off and removed. The appropriate fungicidal spray will protect your plant from further infections.

Gall mites and blister mites are known pests of Fremont cottonwood. Landscape plants can usually tolerate some gall and blister mite damage, and no controls are known for most species. Aesthetic damage can be managed by pruning and disposing of infested leaves. When mites are abundant, it is important to conserve natural enemies and to keep plants healthy and vigorous.

Wetwood disease is evidenced by stained, discolored, or water-soaked areas of wood. Infected bark cracks or wounds may exude a sour or rancid reddish-brown fluid. Severely infected trees may experience foliage wilt and branch dieback. Prevent infection by avoiding injuries to bark and wood. Trees can also become infected through pesticide injection wounds. Note that while symptoms may be unsightly, infected wood is often just as strong as healthy wood.