Tuesday, January 12th, 2016
Whether you own a house, a business, or another type of property in Austin, you should be aware of the most common tree diseases in Austin. You want to know what to watch out for and be ready to call an arborist at the first sign of an issue. Most of the diseases affecting Austin trees are seen throughout Texas and into other areas of the country so this information can help you even if you move in the future.
Among the most common tree diseases in the city, oak wilt is probably the one that arborists see most frequently. It can affect all types of oak trees, but white oaks are the most resistant, red oaks have the highest susceptibility, and live oaks sit somewhere in the middle. Bur oaks, Chinquapin oaks, and Mexican white oaks are all resistant. You look out for signs that your trees have oak wilt, such as leaves dropping, the leaves browning, or the death of the tree. In the case of live oaks, you may also notice veinal chlorosis.
Oak wilt spreads between trees via root grafts, which is why you should always have an arborist do these grafts for you as they will recognize the signs of oak wilt. It can also be spread by the nitidulid beetles. These beetles land on the fungal mats within red oaks that are infected then move onto another oak tree and feeding there on areas with open wounds.
Your arborist will tell you that preventing oak wilt is better than treatment and they can help you outline a plan. If a tree is already infected, you will want to prune it only during extreme temperatures and always disinfect your pruner blades or saw when switching between trees. Painting the wounds on oak trees can also help to some extent as this prevents the beetles from infecting the tree.
Another common issue for Austin trees is a hypoxylon canker. Many native trees are susceptible to this disease, including pecan, oak, elm, and sycamore trees. It can kill trees rapidly and may include thinning of the crown or branch dieback. This disease is most common during drought, at which time it attacks trees that are weakened. It can also decay sapwood. You may also notice the bark starting to fall off the trunk and branches or dark-colored spores in areas where the bark peels.
Trees that develop hypoxylon canker cannot be cured, but you can prevent it from developing. The best way to do this is to ensure that your trees are not weakened, particularly during times of drought. Make sure you give these trees plenty of water when rainfall is minimal and to seal any wounds right away.
Bacteria leaf scorch is one of the rare tree diseases in Austin that is caused by bacteria as opposed to fungus. This disease is spread by insects, particularly leafhoppers. When a tree develops this issue, the water flow between the roots and leaves will be restricted. Several trees, including oaks, elms, sycamores, and boxelders are all susceptible.
The symptoms typically appear during the mid or late summer with a yellow band appearing between the green tissue of the tree’s leaves and its scorched tips. It may cause branch dieback or the leaves to defoliate early. Bacteria leaf scorch can also put the infected tree at a higher risk of secondary pests or infections because of the stress of the disease.
Our arborists can work with you to suppress an infection on your Austin trees. They will suggest you give the trees extra water during times of drought and use mulch to help keep them nourished. If a tree is infected, they will most likely suggest that you remove it from your property.
Another common tree disease within the Austin area is fire blight. This is another type of bacterial disease, but it typically focuses on fruit trees such as apple and pear. You can tell a tree has fire blight if the blooms and foliage rapidly blacken. The shoot tips will also begin to bend and form a hook similar to a candy cane. The branches may also blacken and develop cankers and eventually there will be sunken twigs. Unfortunately, the cankers are able to keep the bacterium in place throughout the winter. When spring arrives, the bacterium oozes out of the cankers, spreading to other healthy areas on the infected tree as well as other nearby ones via rain, insects, and wind.
It is sometimes possible to eliminate fire blight by carefully pruning twigs at least four inches underneath the visible cankers. Be sure to clean the pruning shears thoroughly between every cut and once again after you are done so the disease doesn’t spread. Just be sure not to over-prune as branches and twigs growing vigorously increases the risk of fire blight.
Although not technically a disease, pests such as various insects are a common enough issue affecting trees in Austin that they should be included in this list. There are several main categories of insects that damage area trees. Stipplers tend to feed on the leaves, leading to a stippled, bleached, or bronzed appearance. Lace bugs will feed on the under portion of leaves and leave dark tar spots from the excrement behind. They may cause leaves to fall, but that is typically the extent of their damage. Spider mites are also stipplers. Suckers are smaller insects that are found on the twigs or leaves. They typically leave dew and sooty mold under the tree. Aphids prefer hackberry, elm, crape myrtles and pecan trees while scales like elm and magnolias.
The most obvious sign of chewers is leaf tissue that is missing, leaving behind leaves that resemble skeletons. Bag worms, a type of caterpillar, affect cedar, oak, cypress, and arborvitae trees while tent caterpillars focus on fruit trees. Other chewers include fall webworms and juniper bed worms. Borers like the cottonwood borer and emerald ash borer make small holes in the trunk of the tree, leading to tip dieback and the overall decline of the tree’s health. Finally gall makers leave behind abnormal balls or bumps on twigs and leaves. They include the oak apple gall and hackberry nipple gall.
If you notice any issue with your trees, contact a certified arborist with experience in the Austin area like Austin Tree Surgeons. We will be able to work with you to diagnose and treat the issue.