The oak tree has always been considered the most majestic of heavy-bark trees. The oak is naturally resistant against most common pests and insects found among garden trees. However, an oak tree can occasionally become vulnerable to the following diseases/pests:
Oak Pest Problem: Pit Scales
Pit scales are insects belonging to the Aesterolecanium species. Aesterolecanium are not commonly found in all household gardens. They are endemic to certain soil types and temperature conditions. Pit scales are more common in oak trees grown in humid conditions. The insect is difficult to detect. It appears as small lumps on the bark.
The first sign of pit scaling is the presence of fast-drying leaves and dried-up twigs. Most oak pit scales will have a green and brownish coloration. Aesterolecanium scaling is excessive during the spring season, as the insect multiplies quickly and feeds continuously.
Chemical control is regarded as the most effective solution since organic insecticides are slow to show results against Aesterolecanium. Usually, all insecticides containing heavy concentrations of Acephate are effective.
It is better to spray the oak with oil-based sprays occasionally, even if pit scaling is not present. This helps in immediately killing the eggs of the insects.
Oak Pest Problem: Bark Lice Webbings
The problems are caused by psocids, also called bark lice and tree cattle. Psocids are destructive insects that produce typical silken webbings, found wrapped around the bark. The webbing is not found on the leaves or branches. They should not be confused with garden caterpillars that are seasonal occupants of oaks and don’t cause much damage. Psocids don’t drain nutrition from the tree but feed on useful fungi found on the oak bark. They also feed on surrounding plant matter like mulch.
Noticeable signs include the presence of fine thread-like webbing. Springtime is usually the time when bark lice multiply beyond control. More than nutritional damage, bark lice spoils the appearance of an oak.
Remedy and Prevention
You can use any organic insecticide and seasonally spray it on the bark and the branches. This is the most effective method to get rid of bark lice. Harsh chemical insecticides are rarely needed for this problem.
Common Oak Tree Insects
Oakleaf tier, scarlet oak sawfly (oak slug), gypsy moth, oak leaf roller, and forest tent caterpillar can be found in some garden oaks, but they are not very harmful. They can be easily remedied with a systematic spraying of insecticides, every two months.
Oak tatters affects younger oaks, particularly the leaves, making the foliage look tattered. It is not a common disease among oaks grown in cooler conditions. It can be resolved by using insecticides used for bark lice removal.
A fungal infection affecting young and mature oak trees. Red oaks are more vulnerable to wilting. There are no pesticides that can completely cure this problem. Affected trees have to isolated and destroyed, i.e. the entire part that shows signs of excessive wilting has to be cut off and burned.
Anthracnose is caused by a group of tree-growing fungi. White oak is more vulnerable to it. It presents as brown blotches along the veins of the bark. Specific pesticides are available for curing Anthracnose diseases.