Homeowners cherish their trees as sources of shade, beauty, and significant property value. Unfortunately, trees suffer from various diseases, insect damage and environmental stresses. Our help desk receives more questions about trees than any other subject.
To figure out what might be happening to your tree, you need to become a detective. For example, you may notice that the leaves of one or more of your trees are turning color at the wrong time of year, falling off, or perhaps you notice sap running down the trunk. Before doing anything, such as spraying or adding fertilizer, assess the tree carefully. If you have to call a professional, it will be helpful to have this information.
Master Gardeners may help you diagnose certain diseases and/or insects, but we do not treat trees. You may send pictures of the entire tree and close-ups of the problem area(s) and as much information as possible to our help desk at master.gardener@dentoncounty.gov.
What kind of tree is it?
- If you don’t know what kind of tree it is, this tree guide can help you identify it. Alternatively, send a picture of the entire tree as well as a close up of the leaves to the DCMGA Help Desk at master.gardener@dentoncounty.gov. We will help you ID it.
- Some insects and diseases are host-specific. At the University of California IPM site you can click on a tree species and get a list of common insects and diseases as well as treatment options.
Look for patterns
Part of being a tree detective is looking for patterns of misbehavior. Is the problem restricted to one species, or are many species affected? Most insects and disease-causing fungi and bacteria are somewhat host-specific. When several species are affected, the problem is usually environmental.
Check environmental conditions
- Check soil moisture—too much, too little or just right.
- If there has been recent construction or anything that would disturb the roots, this can cause leaves to begin browning and/or falling off in the area(s) to which those roots supply nutrients
- Have you (or perhaps a neighbor) used herbicides recently?
- Are the roots too deep? There should be a slight flare where the roots meet the soil line.
- Is there too much shade for the species?
- Is it near a pool and pool chemicals?
Where is the problem?
Back away and look at the tree. Is the problem occurring all over, on individual limbs, only on top, only at the bottom, only on one side? Is it the leaves at twig tips, or older leaves? Is there flagging? Or does it appear to be all leaves?
Figure 1: Flagging is a condition where branch tips become brown in a random pattern throughout the tree. (Ronald S. Kelley, Vermont Department of Forests, Parks, and Recreation, Bugwood.org)
Look at the leaves front and back
- Check for spots, holes, blotches, wilting, necrosis (browning) along edges.
- Are they curling?
- Changing color?
- If leaves are falling, are they green or brown?
- Leaves may be brown but remain on the tree; this is important.
- Look for insects (usually on the back side of leaves if present). If insects are found, look for environmental problems that may stress the tree. Diseases and insects often attack stressed trees.
- Look at the stems for signs of cankers, scale insects, or galls. Scrape the stem and check for discoloration.
Inspect the Trunk
Figure 2: Insect damage on underside of bark (M. Nuorteva, Bugwood.org)
- There might be loose bark. If so, look on the back side of the bark and on the bare trunk for insect galleries (pictured).
- Is sap running, or do you see what look like wet spots?
- Are there borer holes or any insects crawling on the trunk?
- Are there cankers? (Cankers are dead sections of bark on branches or main trunks of trees. Bark may be killed by mechanical injuries or by plant pathogens, especially fungi and bacteria. … Canker diseases may cause extensive damage to trees when they kill all of the bark in a particular area, thus girdling a branch or main stem.) Cankers may occur on the trunk, branches or stems.
- Are there mushrooms or anything that looks like a fungus?
Figure 3: Large canker (Joseph OBrien, USDA Forest Service, Bugwood.org)
About Insects
Some insects on your trees can be left alone while others must be removed to protect the tree. For example, borers can kill a tree. They require treatment. Ants, on the other hand, are generally not a problem. Termites, however, feed on dead tissue, and the tree will need further assessment. If you find insects, try to identify them. If necessary, send a picture to our help desk.
More about problems with common North Texas trees
Oak Diseases
Post oaks and blackjack oaks are our native oaks and are numerous in Denton County. There are also many other types of oaks. The Clemson Cooperative Extension Oak Diseases and Insect Pests page has a list of diseases, pests, and insecticide and fungicide options for different diseases.
Pecan problems
There are also many pecan trees in Denton County, and problems are quite common. The Texas A&M AgriLife Extension Evaluating Pecan Problems page is a very good guide to all sorts of issues, including nutritional deficiencies.
For additional help, send pictures and as much information as possible to the DCMGA help desk at Master.gardener@dentoncounty.gov
If disease is suspected, you can send a sample to the Texas Plant Disease Diagnostic Lab at A&M for a small fee. Instructions and a form are located at the Texas Plant Clinic page.
Or, you may call a certified arborist to diagnose and treat the tree.
When is a Certified Arborist necessary?
It can be difficult for the average homeowner to treat an entire tree, particularly if it is large. Certified Arborists are individuals who have achieved a level of knowledge in the art and science of tree care through experience and by passing a comprehensive examination developed by some of the nation’s leading experts on tree care. Certified Arborists must also continue their education to maintain their certification and adhere to a Code of Ethics. Therefore, they are more likely to be up to date on the latest techniques in arboriculture.
Where to find a Certified Arborist: You can find an arborist in your area at https://www.treesaregood.org/findanarborist.
Sources
University of California IPM. Retrieved from: http://ipm.ucanr.edu/PMG/GARDEN/plantmenu.html
Clemson University Extension. Retrieved from: http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2006.html
McEachern, G., Texas Agrilife Extension Fruit and Nut Resources, “Evaluating Pecan Problems”. Retrieved from: http://aggie-horticulture.tamu.edu/fruit-nut/fact-sheets/evaluating-pecan-problems/
International Society of Arboriculturists. Retrieved from: isa-arbor.com
Iowa Cooperative Extension Service. Retrieved from: https://store.extension.iastate.edu/Product/sul3-pdf