Janet Laminack: Mysterious ailment damaging some evergreens in DFW area

 

Italian cypress trees, cedars, junipers and some pines have been stricken by some mysterious ailment. County extension offices, especially here in the Dallas-Fort Worth area, are getting flooded with calls and inquiries.

The symptoms I've seen most commonly are Italian cypress trees with "flagging," which means they have random brown and dead branches throughout the tree.

When trying to determine what is causing a plant problem, there are several things that one looks at, especially patterns of damage. I will go over some of these with you to help you understand what we have ruled out (or not) and why.

When one side of a tree starts dying, check the root area on that side. Have the roots been damaged? Has new construction occurred or was there too much fertilizer or herbicide applied in that side of the root zone? Maybe it's not a root issue, but herbicides drifted from somewhere else on a windy day directly on the foliage. Is there anything different about that side of the tree? Is it in more sun than it used to be? Is it catching more reflective heat?

If the damage is scattered throughout the tree, then we start thinking it may be an insect or disease. In the case of the cypress and junipers, we immediately suspected Seridium canker. This is a fungus that causes cankers on the branches and the dieback occurs from that point out to the end of the branch or trunk. These cankers are not always very visible. You can peel the bark back and typically with Seridium canker, you would see streaking or discoloration in the wood.

That hasn't been the case with many of the samples we have seen. The other usual suspect for this kind of damage on these trees are spider mites. These tiny varmints can cause tip dieback and patchy damage. With severe infestations, sometimes there will be webbing on the plant. Spider mites are visible but not easy to detect. If you suspect spider mites, beat the branch or affected area over a white sheet of paper. If you see little moving dots on the paper, you probably have spider mites. And once again, the trees I examined did not seem to have spider mites. However, spider mites can come in and cause a lot of damage and then be gone.

When damage is widespread, as this has been, we tend to suspect weather events. Many people have been suspicious of the hard freeze we received suddenly last winter. I myself think that might have been a factor, since evergreen plants especially seem prone to being caught off guard by a sudden drop in temperature. It may not be the cold that gets them as much as the dry cold and they desiccate when it is cold, dry and windy.

The other weather event is rain. When we get all our annual rainfall in one week (or so it seems) our soils are unable to drain and tree roots sit in water. They essentially drown, because roots need air.

But what is our final answer? The age old scapegoat answer of "it's probably a combination of factors." We have been having tough weather for plants the past few years in our area. It's been extremely hot, it's been extremely dry, it's been extremely wet, and it's been extremely extreme.

Plants do experience stress and these conditions are definite stressors even on our established native trees. And when plants are stressed they are much more susceptible to becoming attacked and impacted by disease or insects. So, our advice is to keep your plants healthy and eliminate as much stress as you can.

If your tree or plant is already showing stress or damage, don't fertilize it. Plants produce their own food and sometimes fertilizer can cause a flush of growth that doesn't help the situation. With trees, eliminate competition with your lawn by mulching from the base of the tree to the dripline. Water trees deeply but infrequently; let them dry out between waterings. Trees do not like shallow, frequent waterings.

If your lawn is lush and green because of frequent watering, your tree may be stressed or have a shallow root system that puts it at risk for problems. Prune out areas that are damaged, inspect for cankers or spider mites or other insects and diseases. And sometimes, you just have to remove a tree or plant and put something else in that is healthier and happier.

Contact us with your landscape and garden questions, at www.dcmga.com, 940-349-2892 or at master.gardener@dentoncounty.com.

JANET LAMINACK is the horticulture county extension agent with Texas AgriLife Extension. She can be reached at 940-349-2883 or via email at jelaminack@ag.tamu.edu.

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