What is oak wilt?

Oak wilt is one of the most destructive tree diseases in the United States. Oak wilt kills lots of trees in Central Texas. Some say that it’s prevalent in epidemic proportions here. Well, what is oak wilt? Oak wilt is an infectious disease caused by the fungus Ceratocystis fagacearum. This fungus invades and infects the water-conducting system in susceptible trees. All oaks are susceptible to this disease to some degree. Some species are more affected than others. In fact, infections have been found in 16 native oak species.

Oak wilt affects two main types of oak species specifically – the white oak and the red oak. White oak trees have rounded leaf edges and the pores are clogged with tyloses while red oaks have pointed leaf edges. Their pores are large and open. Because of this difference, red oak trees tend to die faster from oak wilt than white oaks.

So, how does oak wilt disease spread?

The oak wilt fungus spreads in two basic ways. First, there is a transfer of spores from diseased to healthy trees by insect vectors and movement of the fungus from a diseased tree to a healthy tree through root grafts. If conditions are right after the oak has wilted and died, spores are produced on fungal mats that form under the bark of the oak. The mats produce asexual spores called endoconidia. Endoconidia are barrel-shaped spores that are produced in chains. If compatible mating types are present, these mats will produce sexual spores (ascospores) in fruiting structures. Certain species of sap beetles are attracted to these mats because they smell fruity.

The beetles will visit the mats to feed and breed. This is where they pick up the disease. These same beetles are also attracted to the bleeding sap of wounded oak trees and can then deposit the spores picked up from the fungal mats. This method of transmission is important for introducing the fungus into a new area which it could not have reached by transmission through root grafts.

Of course, transmission via root graft is the most common means of spreading the disease. Trees within as much as 50 feet of a diseased tree can be infected. Oak wilt usually moves from diseased trees to healthy trees through roots that have become interconnected. In this case, spores that have been produced inside the tree travel through the vascular tissue of a tree. Most root grafts form between oaks of the same species. Red oak develops root grafts more commonly than white oaks and grafts between red and white oaks are very rare.

Next week, we’ll focus on treating oak wilt. If you have questions about this disease, please feel free to call us at Austin Tree Service. Our phone number is 512-341-8888.

A Guide to Our Series on Oak Tree Diseases

oak-tree-and-sunFor multiple weeks, we’ve been focusing on Oak Tree Diseases. We’ve given you plenty of information on them so that you can know what to look for and when to call us in for help. Oak tree diseases are very common, unfortunately, and with the weather we’ve had this year, we expect a lot of calls about them. We wanted to help you determine if you have an issue because we don’t diagnose tree diseases. We just treat them.

Oak trees are very common in Texas. They are a native species and react well to our climate. They are beautiful trees that usually last a very long time. They require basic care such as fertilization, watering and regular pruning to keep them healthy.

The oak tree diseases we discussed ranged from the mildly inconvenient to the truly deadly. We focused on a variety of diseases and encourage you, if you want further information or just need a refresher to read the original article again.

In our ‘study’ of oak tree diseases, we focused on the following:

What we want you to do is to be aware of potential problems that could happen to your trees. We want you to try to catch them early so that we can take a look and see what we can do. We don’t want the problem to get to the point where we have to worry about tree death or removal. We want to be able to save your oak trees. We want to save all of your trees, as a matter of fact.

At Austin Tree Service, we love trees. We want to keep your trees healthy and you happy. We know we can do that with your help. Hopefully, you enjoyed our Oak Tree Diseases series. If you have suggestions for future series, feel free to contact us on Facebook or Twitter. If you suspect or know you have an oak tree disease, please call us at 512-341-8888 so we can take care of it as quickly as possible.

Oak Tree Diseases – Oak Decline

oak-declineOak decline is the last of the oak tree diseases we will discuss in our series. The fungus that causes oak decline is Cephalosporium diospyri. It’s a weak vascular pathogen occurring in Texas Trees. Plants affected by oak decline first show signs of thinning out in the top of the tree. When you first notice it, twigs in the upper portion of the tree will show signs of dieback. It will increase yearly if left untreated.

If the dieback reaches the larger limbs, such as the ones in the main tree canopy, sucker growth will become evident on the main scaffold limbs. If the disease is allowed to progress, only the main scaffold limbs will remain alive. Unfortunately, not for long as they will eventually die too. This can take from five to ten years to happen on live oaks, but can happen quicker on other types of oaks.

Therefore, it’s important that – as soon as you notice the dieback on the twigs – to contact a professional like us to help you keep your tree alive. Oak decline is a tree killer and therefore a very serious oak tree disease. We can be reached at 512-341-8888. Although we don’t diagnose tree diseases, we can work with any one of them once they are discovered.

Did you know that root grafting is suspected as one means of spreading the fungus? Root grafting is the process of grafting a shoot or stem of one plant onto a section of another. We don’t suggest you undertake this process yourself. Bark beetles have also been associated with the spread of oak decline. The fungus has been isolated from the body of these insects. If insects are involved, then this would explain the spread of the disease across areas too great for root grafting and can make oak decline more common than was previously thought. It’s not good news, we can assure you.

Live Oak, Post Oak, Water Oak, Texas Red Oak, Willow Oak, Sycamore, persimmon, Winged Elm, Hackberry, American Elm, and Western Soapberry are reported to be hosts for oak decline. There is not a simple method of identifying the disease at this time.  For the most part, recommendations are based on positive identification of the problem. Mechanical injury to the roots can cause symptoms easily confused with disease caused by other fungi. In newly built areas, the damage most often observed is from root injury.

 Steps to Reduce Live Oak Decline Losses:

  1. Identify the problem.
  2. Reduce the stress conditions that weaken trees.
  3. Optimize fertilizer and water applications to tree.
  4. Remove dead limbs on tree.
  5. Do not import wood from Oak Decline infected areas as it could be a source of the disease spread into a previously disease free area.
  6. Use trees not known to be a host of Oak Decline.

The following trees are known not to be hosts of oak decline:

  • Cotton Wood
  • Pine
  • Bald cypress
  • Arizona Cypress
  • Willow
  • Walnut
  • Hickory
  • Magnolia
  • Cedar
  • Pear (Bradford)
  • Osage‐orange Sweetgum
  • Mimosa
  • Crab Apples Mesquite
  • Hercules Club
  • Redbud Honey locust
  • Dogwood
  • Chinaberry Boxelder
  • Palms Mountain
  • Laurel
  • Catalpa
  • Chinese Tallow
  • Oriental Oaks
  • Chinese Holly

When selecting trees, you should contact the County Extension Agent in your county for those trees that do well. You can also contact us at Austin Tree Service. We know which trees work best in our climate.

Oak Tree Diseases – Oak Wilt

oak-wiltOak wilt is caused by the fungus Certocystis fagacearum. This disease is an important one for all oaks. For example, members of the white oak group tend to die very slowly after the infection occurs and can carry the fungus in the vascular system without showing any symptoms at all. Red oaks, on the hand, die rapidly after infection. Symptoms show up on red oaks in early May as a bronzing of the leaves.

Now, on live oaks, the leaf symptoms are variable. The most common symptom is brown necrosis of the leaf veins. The remainder of the leaf might stay green or it can turn slightly yellow. Severe leaf drop occurs while the leaves are still green. If you cut through the wood, you may see a discoloration in the last annual ring. Symptoms develop usually on one limb or branch and, in time, spread rapidly to the remainder of the tree.

What makes oak wilt so problematic is that the fungus may be carried from tree to tree by various insects and through root grafts. Sap beetles can be important in the short range spread of oak wilt. Red oaks suffering from oak wilt have problems in the later summer or early fall. They develop spore mats under their bark that show up during the spring. As the mats develop, the bark begins to slough off or ruptures. This exposes the fungus. Insects are attracted to the mats. If they move from the mats to healthy trees which have open wounds, oak wilt can then enter the healthy tree and move into water inside the tree, affecting its tissue.

Oak wilt can be difficult to stop or control. You can destroy the diseased trees and remove or burn the stumps. The only secret to protect your trees from getting infected is to properly prune them and seal off the cuts to eliminate sap flow. Neglected trees are more susceptible to oak wilt. Let us help you keep your trees healthy

Oak trees, as a rule, should not be pruned during the spring particularly the months of March, April, May and June. Please give us a call at 512-341-8888 for more information or visit our website at http://www.keepaustingreen.com.

Oak Tree Diseases – Powdery Mildew

mildew_zinnia-269x300Powdery mildew comes from several fungi. They are called Microsphaera alni and Phyllactinia guttata.(Don’t worry – there won’t be a quiz later. We can never remember fungi names either, but they sure make us all sound smart, right?)  Powdery mildew is a very recognizable and common fungal disease. It’s also easily identifiable. Infected leaves have a faint indistinct spot on the upper leaf surface and a white to off-white powdery growth on the lower side. The fungus is often found along the veins and the midribs of a leaf. You will usually notice it in late fall. In severe cases, infected leaves become slightly disfigured.

Powdery mildew is one of the most widespread fungal diseases. From vegetable gardens to rose gardens to oak trees and ornamental bushes, there is almost no tree or plant that is immune to this condition. If you find it on your oak trees, don’t worry. This fungus is host-specific. Just because you find it on one tree, doesn’t mean it is a threat to other trees or plants. There are many different species of powdery mildew. However, they all look the same so we sort of lump them together.

We told you what to look for in the early stages, but what happens in advanced stages of powdery mildew? Well, the leaves can turn yellow, curl or turn brown. This can cause the tree to defoliate, which is not pretty. Powdery mildew likes dry foliage, high humidity, low light, and moderate temperatures. The disease is most severe on trees or plants that are in shaded areas with little to no movement.

While it thrives in humid conditions, powdery mildew does not do well if leaves are wet from frequent rain or irrigation. The most favorable conditions for powdery mildew occur when nighttime temperatures are cool and followed by warm daytime temperatures. Early detection is the best way to eliminate the problem. We suggest that once you notice powdery mildew on your oak trees, that you contact us at Austin Tree Service at 512-341-8888 so that we can help treat the problem. Remember – we don’t diagnose tree diseases, but we can treat tree problems once they are discovered.

Generally speaking, powdery mildew is a mild problem. It does not significantly affect the tree, plant or shrub it is on. It doesn’t really require management. It usually goes away by itself. However, sometimes, because of the condition, photosynthesis can be reduced in the colonized leaves. The best thing to do is to make sure your trees and plants are not overcrowded. You should have us prune your trees regularly to increase light penetration and improve air circulation throughout the canopy. Don’t fertilize if your tree is suffering from powdery mildew. It will just spread the disease.

Sure, powdery mildew may not be a major oak tree disease but many oak trees are affected by it. If your tree suffers from this disease, it’s best to catch it quick and contact us for treatment.

 

Oak Tree Diseases – Hypoxylon Canker

hypoxylon-cankerBecause oak trees are usually shade trees, when they get distressed, they become susceptible to the oak disease, hypoxylon canker. The specific species of this fungus is called Hypoxylon atropunctatum. It’s common in Texas due to the fact that Live Oak, Red Oak, Blackjack Oak and Post Oak are common types of trees that make up a significant portion of the urban tree population. It appears on trees that are easily stressed or intolerant to environmental changes.

The disease first shows up as a light brown or tan area that is dry or dusty when disturbed. This is called the asexual phase of the hypoxylon canker. These are the spores of the fungus. They can travel far distances in wind-driven currents. When these infections first develop, the bark becomes paper thin on the surface of the cankers and flakes off, exposing a brown fungal patch. Within a few weeks, the light brown dusty area turns a silvery-gray color with scattered black spots – we call this the sexual stage. The canker, at this point, is hard to the touch.

Hypoxylon atropunctatum is generally a weak parasite and will cause no problems to healthy trees. The tree can defend itself from the canker with normal defense mechanisms. The canker appears rapidly on the exterior of weak or dead limbs. The organism lives harmlessly in the outer bark tissue and aids the tree in quickly shedding or discarding the limbs. If the hypoxylon canker appears on limbs or branches, it’s not considered lethal. It’s often removed by getting rid of the dying or dead limbs.

When the disease appears on the main trunk or the stem of a tree, then the tree is dying or nearly dead. It is rare for a tree to recover from hypoxylon canker if it appears on the trunk or stem. Why? The main trunk carries moisture and nutrients up the tree. The outer layer of the trunk, under the bark, is only a few cell layers thick and constitutes a tree’s current growth ring. The canker on this part of the tree means that there’s something seriously wrong with the main transport system. The tree is not able to sustain itself and dies.

Hypoxylon canker does not spread from tree to tree as is commonly believed. The fungus already lives in the outer bark of most healthy Oak trees.  It should be noted that any portion of a tree where Hypoxylon Canker appears, the wood will dry out quickly. It becomes brittle and dangerous.

There is really no cure for Hypoxylon Canker. Removing dead and weak limbs, as well as maintaining overall tree health, will be the best way to deal with the problem.  You should make sure that you’re doing the following to avoid this problem from getting out of hand:

  • Regularly and aggressively provide deep root fertilization for your tree.
  • Prune trees to eliminate any weak, dying or dead limbs.
  • Avoid injury to the trunk and limbs of the tree.
  • Avoid reductions or additions of soil in a tree’s root zone. This keeps the bark tissue from breaking down.

If you suspect your tree has Hypoxylon Canker, please contact us at 512-341-8888. We will be happy to help treat your tree. Remember, we don’t diagnose tree diseases, but we can prune and help improve the health of your tree.

 

Oak Tree Diseases – Burls

warty-burlsBurls can happen on oak trees, usually white oaks. They are caused by the fungus phomopsis. Burls are large swellings on the limbs and trunk. Sometimes, they occur naturally over young buds. Truthfully, the biology of burls is not well known. They don’t always negatively affect a tree and can even add a bit of character or beauty to it.

For some reason, the cambial growth, whether it’s due to environment or infection, is hyper-stimulated. The tree’s growth hormones get disrupted when the metabolism of the tree is hijacked by some other organism like a virus, fungus or bacterium. A ball of extra bark is built. Burls can grow to a great size or they can remain rather small. The largest burls occur on Redwoods and can encircle the entire trunk.

Burls can be removed by pruning or surgery. They contort the grain of wood and are actually prized in some circles. Furniture makers love them because they can add a lot of character to their pieces. Trees can carry this tumor-like growth and still look healthy above and below the growth. Oak burls can often mill out defective burls with rot and holes. You will probably want to get rid of these.

Sometimes, people sell their burls to artists, furniture makers or wood workers for cash. However, oak burls usually need to be removed. The crown gall bacterium is responsible for many burls. It comes with a little extra DNA, called a plasmid, which infiltrates the tree’s genetics. It prompts the tree to make special amino acids and growth regulators to produce the burl. The burl is obviously the preferred habitat for the bacteria.

However, figuring out what causes a burl can be difficult. The bacteria or fungus that started it can be long gone by the time the burl is formed. Burls can occasionally be associated with dormant buds, but that doesn’t explain why they get formed. Truthfully, we can tell you if you have a burl once it’s formed and we can remove it for you. We can’t figure out what caused it and if you are going to get more of them.

Research has shown that, by doing the regular things to keep a tree healthy such as pruning, fertilizing and watering it, will prevent burls from growing. Cutting a burl off will not damage the tree. It’s like taking a benign growth or wart off your skin. Burls take a long time to form, sometimes as often as 30 – 40 years. The sooner you notice the burl, the sooner we can take action.

Give us a call at 512-341-8888 if you have a burl on your tree and want it removed. We are happy to help you.

Oak Tree Diseases – Actinopelte Leafspot

actinopelte-leafspotDuring the hot Texas summer, plants can struggle with a pool of pathogens. Tubakia dryina, also known as Actinopelte Leafspot, is a pathogen most prevalent in red oaks but it can also infect white oaks and other oak variations. This disease can endure the mild Texas winters. Overwintering spores are dispersed once the summer rolls around. The spots are generally small (2 to 5 mm in diameter). They are round and reddish-brown in color. Some have a yellowish halo that surrounds the infection site. The disease is most severe in late summer and early fall.

Those spores that get dispersed in summer occur when it’s moist and wet. Since we’ve had a lot of rain this year, you might see it popping up on your oak trees. Usually symptoms occur at the bottom of the tree or within the trunk. They are the most favorable areas for the pathogen.

Actinolpelte leafspot is known to show up on trees that are under immense stress. If a tree is low in iron, it can become susceptible to Actinopelte leafspot. The fruiting structures can spread to leaf veins where they cause the most damage. They can kill leaves. Sometimes severe defoliation occurs. Actinopelte leafspot can infect trees that have fallen off the tree as well as leaves that are still on it so you’ll want to remove both the infected leaves on the ground as well as those on the tree.

On occasion, Actinopelte leafspot can be confused with Anthracnose, which we dealt with last week. (For more information on Spot Anthracnose, visit this article.) However, the spores from this disease are rather distinctive and can be easily deciphered under a microscope. Remember, we don’t diagnose tree diseases, but if your tree is sick, we can figure out the best course of action to take.

This disease can cause extensive damage, but it is not usually fatal to the live oak. Infected leaves should be destroyed and the tree should be fertilized slightly more than normal to stimulate new, healthy growth. Check your foliage for minor element deficiency. Newly planted trees, those planted within the first three years, are more subject to attack by this disease than well-established trees.

At Austin Tree, we will help you get your tree back to good health. If your tree has a fungal disease like Actinopelte Leafspot, we will make sure to get rid of the foliage infected. We will also suggest fertilization for your trees. Please call us at 512-341-8888. Again, we don’t diagnose tree diseases but we can treat infected trees.

 

 

Oak Tree Diseases – Spot Anthracnose

spot-anthracnoseWe are beginning a series on Oak Tree Diseases. This article is the first of several. We have seen an increase in tree problems, especially among the oak tree family, because of all the rain we’ve had and we want you to know what to look out for. Ready? Let’s go.

Spot Anthracnose comes from the fungus Elsinoe quercus (now that’s a mouthful). Infection by this fungus can cause small spots on the foliage of red oaks. It’s often seen on trees that grow in partial to full sun; it is rarely seen on trees growing in full shade. The spots are only on the upper surface of the leaf and are blackish-brown in color.

The defining factor of the spots of Spot Anthracnose is that the centers of the spots are lighter in color and are about 1 millimeter in diameter. Symptoms are usually visible in early June and increase in number until the middle of August. If you wait that long, the foliage becomes severely damaged and the foliage begins to all off. Defoliation will occur when the infection becomes severe. The tree will take on a pale yellow color and will not look healthy.

Although we don’t diagnose tree diseases at Austin Tree Service, you will probably want to call us if your tree shows signs of Spot Anthracnose. We can come out and perform some much-needed services to the tree.  Sanitation is important in the prevention and control of Spot Anthracnose. All diseased leaves need to be removed. Spraying is not usually required. Trees which have been severely damaged by Spot Anthracnose should have additional fertilizer added to stimulate new growth.

Our best advice is that as soon as you notice the brown spots to give us a call at 512-341-8888. Remember – we don’t diagnose tree diseases, but we can prune the tree of the diseased leaves and prevent it from spreading to the rest of the tree or making the trunk a pale yellow color. By then, your tree needs so much more work and, although we can do it, we’d prefer to catch your Spot Anthracnose early.

We’ve given you the signs to look out for. Now you have to watch your trees to keep them from getting too damaged from Spot Anthracnose. The best thing you can do to prevent the disease is to plant it in the correct location and make sure you care for it by watering it and giving it fertilizer.

We’ll have more about oak tree diseases in the coming weeks. If you ever notice a problem with your tree, call us. We can do our best to prune diseased leaves and branches and will remove trees that are too damaged by disease. Visit our website at http://www.keepaustingreen.com for more information on our services.