Dutch Elm Disease
Dutch Elm Disease (DED) is caused by a fungus that affects Elm trees. The American elm is the most susceptible to this disease, with cedar elm being only moderately susceptible. This disease prevents elm trees from transmitting water from the roots to the crown and eventually causes them to wilt and die, progressing through infected trees very rapidly. A specimen showing early symptoms will typically die within six to eight weeks.
How the Disease Spreads
The disease spreads in two ways - insect vectors and root grafts. The North American Elm Bark Beetle and the European Elm Bark Beetle are the two insects that typically spread the fungus from tree to tree. The European Beetle, which can travel approximately 2,000 feet in their lifetime, is the most prominent in Flower Mound. It is not uncommon for two generations of the beetles to emerge in a typical growing season. In theory, it is possible for the beetles to spread the disease several thousand feet in a growing season. The beetles live and breed under the bark, and they usually target weak or stressed trees. This is why any known diseased trees should be removed and properly disposed of so the beetles don’t have a place to breed. Removal of non-infected, yet stressed trees, is also recommended.
The second way the disease spreads is through root grafts. Roots of trees in close proximity tend to touch and overlap. These roots commonly graft together and share nutrients and water. The grafts can also allow the fungus to move from one tree into another. In cases where several elm trees are located in close proximity, the disease will continue spreading until all of the trees are infected. If one tree is not showing signs of the disease, it is possible to save that tree by severing the root grafts and removing the infected trees; although, this is challenging and should be done quickly after the infected trees are identified.
Contact Us At this time, it is important that the infected trees are identified and removed to reduce the spread of the beetles. Very little research has been conducted regarding Dutch elm disease in Texas and little is known about how the disease will progress through the state. Early observations indicate that the disease is not slowing down, and is causing damage on both public and private land. For more information, please contact the Town of Flower Mound’s Environmental Resources division at 972.874.6352.
Bagworms can be seen hanging from the twigs of a variety of trees and shrubs. They are recognized by the distinctive 1.5 to 2 inch long spindle-shaped cocoons that they make. The cocoons are made from a combination of silk that they spin, along with leaf, twig and bark material from the host tree that they are feeding on. A wide range of broadleaf and evergreen trees and shrubs serve as hosts for bagworm species. These include arborvitae and other ornamental conifers, box elder, cedar, cypress, elm, fruit and nut trees, juniper, live oak, locust, maple, persimmon, pines, salt cedar, sumac, sycamore, wild cherry, willow, and many other ornamental plants.
This list is pretty extensive and includes many trees found within the Town of Flower Mound. A host plant will have an increase in bagworms each year because the females don’t fly. The bagworms may become abundant enough in some years to completely defoliate their host plant. This is a real concern for evergreen trees (those that retain their leaves through winter) and might eventually lead to premature death of the host plant. Deciduous trees are better able to cope with the damage left by bagworms because they have the ability to generate new leaves to replace those that are been damaged by bagworms during the same growing season. Dispersal of bagworms to new host plants occurs when young caterpillars hanging from silken threads are spread by wind. This process is called ballooning. Caterpillars can also be spread by birds.
There are multiple methods of treatment for bagworms but the Town of Flower Mound advocates those that are the least harmful to the environment. The best control method would be to remove the cocoons hanging from tree limbs during the fall, winter and early spring time, before the eggs hatch. Some of the cocoons will contain a female bagworm and/or 300 plus eggs. When many small bagworms are present and feeding, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long), usually in May to early June for North Texas. Small larvae are more vulnerable to insecticides, and feeding damage is relatively minor. Carefully inspect susceptible landscape plants. Young bagworms are hard to see at first so look closely for the small, upright bags during the spring months. They will have the appearance of tiny ice cream cones made of bits of plant material.
Fall webworms are another caterpillar that may be confused with bagworms. Fall webworms are most readily found in pecan trees throughout the town. They also have been observed in elm, cottonwood, mulberry, and redbud trees. The female moth will lay a cluster of a few hundred eggs on the underside of the leaves of a host plant in the spring and the eggs hatch approximately one week later. After hatching, the larvae immediately begin spinning silken webs for protection from predators while they are feeding. The caterpillars will skeletonize leaves so that only the veining structure remains. The webs initially start at the tip of branches and can eventually extend all the way down to the trunk of a tree.
The best way to deal with fall webworms is to physically break open the webs and allow birds and other predators to eat the caterpillars. This can be done with handheld tools if the webs are lower in trees, or with a high-pressure water hose for those webs in the upper parts of trees. This process may need to be repeated several times throughout the growing season, but can be effective at controlling webworm populations in individual trees. Pesticides can also be used to control fall webworms. Consult with a certified arborist if this type of treatment is desired.
Resources Additional information about bagworms and fall webworms can be found at the following websites:
- Kansas State Home Horticulture Bagworms
- AgriLife Bagworms
- AgriLife Webworms
- Texas Agricultural Extension Service
DroughtDuring drought conditions, established trees and native trees, which typically don’t require additional irrigation during normal rainfall conditions, need to be watered periodically. The Town’s Parks Services Department keeps a close eye on trees in Town parks and increases watering, as needed. Residents of Flower Mound are encouraged to do the same with their trees.
Signs of Drought
It is important to understand the signs of drought stress in trees and know if a tree exhibits signs of drought stress; it does not necessarily mean it is dying. Trees are capable of doing what is necessary to protect themselves. Dropping their leaves and going dormant during a drought is one way that they do that. However, It is still important to water these trees during this time even if they are dormant. Signs of drought stress in trees include: browning or yellowing of the leaves, wilting leaves, and losing leaves earlier than normal.
What To Do If you have trees that are exhibiting signs of drought stress, or if you have trees that appear healthy but are not receiving regular irrigation, it is a good idea to use a hose at low pressure to water the critical root zone of you trees. The critical root zone is typically about 12 inches in depth and extends from the trunk of the tree to the edge of the branches; also know as the drip line of the tree. Additional information about watering your trees during severe drought can be found on the Texas Chapter of the International Society of Arboriculture website.
Mature, established trees should be watered once a week during periods of drought, and newly planted or young trees should be watered twice a week.
In addition to watering, using mulch over the critical root zone of your trees can go a long way toward helping them cope with drought conditions. Mulch can aid in moisture retention, reduce temperatures in the soil around the roots, improve soil conditions, and reduce soil erosion. Just remember not to put mulch against or around the trunk of the tree. Contrary to popular opinion, a mulch volcano or mound around the trunk of the tree is not a good thing. Mulch should be kept about a foot away from the trunk. Roots are used to a moist layer around them, but the trunk is not. Also, the mulch layer doesn’t need to be any more than 2 to 3 inches thick. Mulch that is too thick can actually keep moisture from reaching the roots and can even suffocate the tree.
For more information on tree care, contact the Environmental Services Division at 972.874.6352, or visit the Texas Forest Service website.