Oak wilt is a non-native, fatal disease of oaks. It can kill red oaks quickly, and if left unmanaged, can devastate an oak forest and promote conversion to buckthorn and maple. Oak wilt symptoms can frequently resemble damage from the native twolined chestnut borer, which commonly infests stressed oaks.
Oak wilt is an aggressive disease that affects many species of oak (Quercus spp.). It is one of the most serious tree diseases in the Eastern United States, killing thousands of oaks each year in forests, woodlots, and home landscapes. Oak wilt was first identified in 1944.
Oak Tree: Pest Issues
From foliage-munching caterpillars to sap-sucking aphids and scale insects, these pests can cause significant damage. Wood-boring borers threaten their structural integrity, while gall wasps create abnormal growths.
Identification and symptoms
Adult oak pinhole borer beetles are 5-8 mm long, somewhat rectangular, and are pitch-brown to almost black. Compared to oak-feeding bark beetles (Scolytinae), P. cylindrus are usually larger, with an elongated pronotum and a prominent head.
Look for wilting, yellowing, and premature leaf drop. Cankers may form at the base of the trunk, accompanied by a distinct mushroom growth near the tree base, particularly during wet conditions. Caused by various Armillaria species, this is an opportunistic disease because the fungus targets weakened or stressed trees.
Oak Wilt Identification
Leaves may droop, roll lengthwise and wilt. Leaves may also die from the tip down. As the disease progresses down the tree's canopy, upper leaves will turn yellow and fall off. Green leaves will fall off too.
There are a few ways to control oak lace bugs if you wish to do so. You can use high-pressure water to knock the insects off plants, there are also several different insecticide treatments you can use (but keep in mind that these can impact beneficial insects as well).
If the leaves of your oak tree turn brown or black, this is a sign that the tree is dying. Other signs include a sudden decrease in the size of the leaves and a sudden change in the shape of the leaves. If you notice any of these signs, it is essential to contact a tree service company as soon as possible.
Vertical cracks, seams, dead branch stubs and large, older wounds suggest internal decay. Severe damage to the main trunk often warrants removal of the tree. If the damaged area is less than 25 percent of the circumference of the trunk, the wound could gradually heal over and no permanent injury should result.
Many tiny holes in tree trunks and branches may indicate bark beetles; larger open tunnels filled with sawdust-like boring dust (frass) indicate clearwing moths; flatheaded or roundheaded borers leave wet spots and dark stains and D-or 0-shaped emergence holes.
Properly-timed bark sprays with contact insecticides can prevent infestation of susceptible trees and shrubs. Pyrethroids including bifenthrin (Onyx®, (Talstar®) and permethrin (Astro®) work well. Chlorantraniliprole (Acelepryn), is an effective, bee-friendly option.
By the time fine wood shavings accumulate on branches and at the base of a tree, the tree can no longer be rescued. Insect borers have already eaten most of the living tissue beneath the bark that moves water and nutrients throughout the tree.
As with the red oaks, death can occur with a sudden browning of leaves throughout the entire crown, or more slowly with gradual leaf loss. P. ramorum infection in twigs can lead to shoot tip dieback or a shepherd's crook. Secondary organisms are likely to attack weakened and dying trees.
Armillaria root rot, sometimes called oak root rot fungus, can survive for many years in wood debris or dead stumps and root systems. It spreads to new trees of many species through root contact. It causes decay of roots and lower trunk eventually killing the tree and causing a toppling hazard.
One phosphonate fungicide, Agri-Fos, is registered as a preventative treatment for P. ramorum for use on individual, high-value tanoak and oak trees. Treatment is not recommended in areas where infested plants are not already present.
Once an oak tree is infected with the oak wilt fungus, the tree will die and there is no treatment to save the tree. When an oak wilt infection is confirmed treatment can be applied to the surrounding trees to prevent the spread of this disease.
How long do oak trees live? Oak trees can live for over 1,000 years; however, a more normal age would be around 600 years. It is said that an oak spends 300 years growing, 300 years living and 300 years in slow decline.
Shapes of galls vary from spherical to urn-shaped to star-shaped to fuzzy. Inside the galls are the eggs and larvae of the insects. Galls are made of plant material and vary in colors of yellow and green and turn tan-brown as the development continues. Galls will eventually brown and die once the adult insect emerges.
Corrosion and pitting will appear as dark spots inside the barrel. If they are visible to the naked eye, the barrel is in bad shape. Minor to moderate pitting will not be visible, although it can often be seen just inside the muzzle near the crown.
Previously unrecorded damage to oak, Quercus spp., in Southern California by the goldspotted oak borer, Agrilus coxalis Waterhouse (Coleoptera: Buprestidae).