I recently came across a big patch of live oaks infected with oak wilt in Richardson, Texas, and was reminded of how little common knowledge there is about such a prevalent and insidious disease.
Oak wilt is a disease lots of people have heard of but don’t know much about, except that their sense memory of it is very bad. So we’ll start with the basics.
What Is Oak Wilt?
Oak wilt is a vascular fungal disease that affects oak trees. The fungus clogs the vascular system of the tree, blocking the transportation of water and nutrients to the canopy. Because it invades the vascular system, it is impossible for only one part of the tree to have the disease.
How Does It Spread?
Oak wilt spreads in two main ways: root grafting and beetles. Many people are aware of a prescribed season for trimming oaks, roughly July-January. The reason February-June is not an ideal time to trim oak trees is the nitidulid beetles that can carry the fungus from infected trees to uninfected trees are active during this time. The beetles are attracted to any wounds on an oak, so if trimming must be done during this time-frame, all wounds should be sealed with pruning paint. Although cleaning tools between trimming different trees is part of most guidelines on the subject, it is thought by some experts that it would be nearly impossible to spread via trimming tools.
Root grafting is by far the most common method of transmission. It is when root systems from two different trees coming together and join, which is very common for trees in close proximity to each other.
Wood from a tree that has died of oak wilt cannot spread the disease unless the tree is a red oak. Fungal mats of oak wilt can only form on red oaks, so any wood from a red oak killed by the fungus should be burned.
Trenching can sometimes be used as a preventive measure in conjunction with other treatments, but it is usually only viable in field settings. The trench must be at least four feet deep and there must be at least 100 feet between trench and the first symptomatic trees, which will rarely work well in a city.
Fungicide injections, which are the only method of treatment, can also be applied preventively. Healthy trees shouldn’t be treated until oak wilt is identified within 200 feet, so effectively not until it’s on your block. Even preventive treatment doesn’t always work, but if your tree is a white oak or a bur oak, as opposed to a red oak, it is very likely they will survive.
Oak wilt only affects oaks, but it can invade all species of oak. Some species weather the disease better than others, with red oaks faring the poorest and white oaks faring best. Red oaks usually die within six weeks, while live oaks usually die within six months to a year. Post oaks, chinkapins, and bur oaks almost never die of oak wilt. In a natural stand of trees, about 15% of live oaks will be unaffected although we don’t understand why.
The only real treatment for oak wilt is injection of a fungicide called Propiconazole. The best-known brand is Alamo, but there are other brands as well. The injections should be made via macro-injection in the root flares for best results. The fungicide arrests the progress of the fungus in every part of the tree with working vascular tissue above the injection sites. The fungicide can’t flow downward, so the roots can still transmit the fungus to other trees. Treatment doesn’t always mean the tree will survive. If there are symptoms in more than thirty percent of the canopy, the tree has a greatly decreased chance of survival, as it means that at least that much of the vascular system is already compromised.
According to recommendations by the Texas A&M Forest Service, injections should be done twice, with a two year interval in between. Any other treatments won’t affect the survival of the tree.
Hopefully this post is informative for you, but contact an arborist (preferably one who is oak wilt certified) with any other oak wilt questions or concerns!
Hannah Davis, a certified arborist for Dallas Tree Surgeons, was recently featured in a news story on CBS with Jack Fink about some of the effects that the recent rains are having on trees.
“Drought, Then Rain, Toppling Texas Trees
July 6, 2015 4:00 PM
RICHARDSON (CBSDFW.COM) – A giant pecan tree suddenly fell onto Drew Dodson’s house in Richardson. And it’s not even his tree. It once stood in his neighbor’s yard. “It broke from the roots,” Dodson said. “When it fell, it pulled this straight up.Lucky for Dodson, he and his family were not home at the time. But he did have to hire crews to cut up what was left of the tree and remove it from his property. Dodson pulled off a tarp from his bathroom skylight to show more damage. “I could have been brushing my teeth right here when that tree fell,” he said.
Hannah Davis is a certified arborist with Dallas Tree Surgeons. “I’ve never seen a pecan this big fall over,” she said.
According to Davis, the number of calls Dallas Tree Surgeons has received about falling trees has jumped by as much as 40 percent this year. “We’ve never had a rash of isolated, a few days apart, giant trees falling like this,” she added.
Davis said that you can blame the weather.
The extended drought that Texas was in had weakened the trees, Davis explained. Then, with all the recent rain we had received, the trees became heavy and saturated — and toppled over.
Now, Davis is advising Dodson on what he can do to keep his own trees from falling over, which, as he has learned, can happen without warning. “I don’t think it takes much of a storm,” Dodson said. “If they’re ready to go, you better not be standing under it.”
Experts suggest that homeowners keep an eye on their trees. Look out for dead limbs, trunks that are leaning and spots where the ground is lifting up around the trees. Also, have your trees trimmed, and consult with a certified arborist.” From CBS site
As spring begins, trees are starting to bloom, so take a minute to notice the conditions of newly sprouted leaves. These leaves are an important indicator of the over all health and condition of the tree. If you notice browning around the outer edges while the center of the leaf is still green or a yellowish border it may be bacterial leaf scorch.
Bacterial Leaf Scorch is caused primarily by leafhoppers. These insects having piercing mouth-parts that allow them to suck water and nutrients from trees. Once a leafhopper comes into contact with the bacteria (Xylella fastidiosa) from a previously infected tree is transmits it to other trees during feeding. The bacteria then infects the xylem which is the water transporting system of the tree.
Bacterial Leaf Scorch may eventually kill a tree if not treated. There is no cure for it, but can be controlled through the use of systemic bactericides. This may take several treatments, but once contained it may only be a yearly application. Catching this problem early makes it easier to manage, so take a minute every once in a while to look up.
Call Dallas Tree Surgeons today if you suspect your tree is infected or it is stressed and one of our Certified Arborist will come out for a free evaluation.
Dallas Tree Surgeons is seeing an increase in tree care needs in Plano and surrounding cities (Allen, Frisco, McKinney). The population explosion of the 1990s that occurred in Plano led to many homes being built and many young trees being planted simultaneously. Red Oak, Live Oaks, Cedar Elms and Pecans are just now reaching maturity. Homeowners in Plano are finally beginning to experience the full benefits of mature trees. A few of these benefits are a reduction of utilities, reduction in sound pollution, an increase in privacy, and increase in shade, and beautification of the streets. These native Texas trees set Plano neighborhoods apart from others and increase property value however they also require more care. To see a list of big tree in Plano visit https://www.plano.gov/935/Big-Trees-in-Plano. These large trees require trimming, repair from storm damage, cabling, and plant heath care (i.e. deep root fertilization, sick tree treatments, soil aeration) as they age to maintain their health and beauty (make sure you use an ISA certified arborist). Other trees planted that tend to grow quickly or are not native to Plano Texas such as Bradford Pears and Maples are starting to become diseased, dangerous, and die requiring advanced plant health care, removal and planting new trees to replace them. To adopt a tree in Plano visit https://www.plano.gov/921/Adopt-a-Tree. The variety of tree service needs in DFW vary so much from city to city and Dallas Tree Surgeons offers a full spectrum of tree service.
We covered some great shade perennial groups in “Shade perennial plant selections (part 1).” Here in part two we’ll discuss some Texas native shade-loving plants. As natives, these perennials have few if any insect or disease problems making them virtually care free.
American beautyberry (Callicarpa Americana) makes a beautiful understory shrub that needs lots of space because it does not respond kindly to hedging. This native Texan has a mature height and spread of 4 feet. Its long arching branches are best in the fall when they are weighed down with glossy purple fruits. These fruits are an important food source for migrating birds.
Turk’s cap (Malvaviscus arboreus var. drummondii) is a stunning native medium-sized shrub that tolerates even the deepest shade. It works well as an accent or mass planting. In North Texas, it dies to the ground in the winter emerging in late spring to reach a height and spread of four feet. It has unique vermillion red flowers that give the plant its name. Hummingbirds can’t resist its blooms that continue all summer.
Soapwort, aka Bouncing bet (Saponaria officinalis) is an easy to grow Texas herb that loves partial shade. It grows to about 2 feet high and has a spreading habit. It has pretty pink and white flowers from late spring through early fall. Soapwort gets its name because cleaning materials can be made from its roots and stems. In the past it was used to clean old lace, tapestries, and beer mugs. It will have some die back in the winter, but usually maintains some green leaves. It spreads by rhizomes, but is easy to keep under control by simply pulling up the unwanted offspring.
Sweet woodruff (Galium odoratum) is another Texas herb that makes a great shade groundcover. It will even grow beneath a Magnolia. It may suffer a little winter damage in North Texas, but mulching will help minimize this. It gets 6 to 12” high with a 12-15” spread. Clusters of tiny white flowers float above its whorls of pointed leaves in the spring. It adds a wonderful fine texture to the shade garden.
Frogfruit (Phyla nodiflora) is a low-growing native groundcover with tiny white flowers smaller than the bees that feed on them. It’s mostly evergreen in North Texas, reaching a height of 3-4” with a 12” spread. Because it tolerates foot traffic, it makes a great choice for planting between stepping stones. It does not tolerate being cut back and will require supplemental watering in our hot summers.
Inland seaoats (Chasmanthium latifolium) is a great plant if you want to add grassy texture and movement to your shade garden. After winter makes it unsightly, cut it back to four inches tall. You’ll see new growth in March. In the fall, its big drooping seeds are a lovely color somewhere between gold and white. It’s a manageable height for ornamental grass at only 2-3 feet and makes a great mass or accent plant.
For low-maintenance shade success you can’t beat these Texas natives. Happy planting!
In North Texas we love our shade. It provides much needed protection from our hot summer sun. But, “What can I get to grow under my tree?” is a question we often hear. Shade is a limiting environmental condition just like soil condition, moisture, and temperature. So, we must consider it when choosing plants for our shade gardens. In this first part of our favorite shade perennial selections, we’ll discuss some plant groups that offer shade success.
It’s important to determine what type of shade you have under your tree. At one extreme, we have full shade. Full shade lasts all day with little or no direct sunlight reaching the ground at any time. An example would be areas under decks or covered patios on a house’s north side. Part or medium shade exists when direct sunlight is blocked most of the day. An example of part shade would be an area under a mature shade tree that only receives direct sunlight in the morning or evening. Finally, light shade is present when an area is completely shaded for only a few hours each day or receives filtered sunlight most of the day. An example of light shade would be an area under a solitary, lightly branched tree. Once you know what type(s) of shade you have, you can make better plant choices.
Simply put, perennials are plants that come back or persist for many growing seasons. While some keep their leaves year round, many of them die back each winter and regrow from their roots the following spring.
Hellebores or Lenten rose are evergreen perennials that are one of the earliest to bloom. While not roses, their common name is appropriate because they can be seen blooming during Lent, when most plants are just starting to peak out of the ground. They grow very slowly at first, but are completely trouble-free once established. They reach a height of 24” with an 18” spread. And, they are available in a wide variety of bloom colors including pink, yellow, red, purple, white, and green.
Hostas are popular shade garden choices that come in an unbelievable number of varieties with a broad range of size, texture, and color. Their dense leaves cover the ground from late spring until winter. In North Texas they die back to the ground and emerge in early spring. Their only flaw is a susceptibility to slug and snail damage. Favorite varieties for our area include Honeybells, Sugar & Cream, So Sweet, and Francee.
Heuchera or coral bells are great perennials for outlining the front of a bed. They grow in low dense mounds of rounded or heart-shaped evergreen leaves that range in color from chartreuse to pink to terra cotta to bronze. Mature height is 18-30” with a 12” spread. Flower stalks emerge with beautiful, long-lasting bell-shaped flowers in pink, red, or white. To encourage continuous blooms, remove spent flowers at their stem’s base. Hummingbirds love these native flowers, and they have few pest or disease problems.
Ferns, as a group, love shade and add interesting texture. One of the best selections for dry North Texas is autumn fern (Dryopteris erythrosora). This evergreen fern offers striking seasonal changes. Its new fronds are coppery red. As they age, they fade to dark green. At maturity, the plant is 1-2 feet high with a equal spread.
Before making the trip to your local gardening center, please read our blog post “Prepping a shade perennial bed under a tree.” It will give you some great tips on getting that bed ready to produce beautiful perennials and protecting your valuable tree. And, remember to check out some native Texas shade plants in the second part of shade perennial selections.
Prepping a shade perennial bed under a tree
We love trees and the shade they provide. But, when it comes to getting plants to grow under mature shade trees, many of us are at a loss. Here we want to discuss how to prepare your under-tree planting bed to grow beautiful perennials and still preserve the health of your valuable tree.
Your first thought may be to vigorously trim that tree in an effort to get sun on the ground beneath it. However, clearing out too much of the tree’s crown can adversely affect the tree’s health. The best way to avoid this is to hire a professional tree service with properly trained arborists and tree workers like Dallas Tree Surgeons. We can help you trim the proper amount to get more light under the tree without causing damage by over-trimming.
Once you have the tree properly trimmed, it’s time to plan and build your planting bed. Larger is better. A nice large bed will give your perennials a chance to spread out, and a broad area of properly applied mulch under your tree is one of the most beneficial practices for your tree’s health. Select a wood chip mulch, not rocks or rubber. Such inorganic mulches do not improve soil conditions and keep the root zone too hot. Also, when applying your organic mulch, keep it away from the tree’s stem and root flare. Covering these areas may lead to bacterial or fungal infections and insect infestations. It may be tempting to raise the grade and build a deep planting bed under your tree. DON’T! Your tree’s roots need access to oxygen to use the carbohydrates generated by photosynthesis. If roots are cut off from oxygen long enough, they will die. Your bed, including soil and mulch, should not add more than four inches to the existing grade under your tree. So, a large, shallow bed is much better than a small, deep one.
If you have an existing lawn or weeds under your tree, place newspaper 2 to 3 sheets thick on the lawn under your new garden soil and mulch. This will help smother the grass and weeds without smothering the tree’s roots because newspaper decomposes quickly. Landscape fabric or plastic are not good alternatives because they will create a barrier between your tree’s roots and the oxygen and water they need.
Now that you have your bed’s soil and mulch installed, it’s time to bring on the plants! We will explore shade perennials that grow well in North Texas in future blog posts. When planting under a tree, it’s best to plant smaller nursery stock, not larger than 1-gallon pots. This will reduce root competition between the tree and your new perennials and minimize any disturbance to your tree’s precious roots.
It may seem like a lot of work, but properly preparing your under-tree perennial bed will provide you with a cool, beautiful spot to enjoy nature for years to come. Don’t forget the bench!