Extreme weather is stressing out our trees

Extreme weather is a stressor that can lead to the death of trees, even years later, when impacted by insects and disease. MESSENGER ARCHIVES

Well, here in Wise County and all over North Texas, we have been experiencing trees of many types that are dead or dying. 

On a weekly basis I witness trees like post oaks, red oaks, cedars, cypress, juniper spruce, ash and pines that are succumbing to environmental stressors which can, and most often does, lead to secondary stressors like disease and insects. I conduct many site visits each week looking at trees in decline.

Trees have a vascular system called phloem and xylem. These vascular tissues transport nutrients up and down the tree. Xylem transports and stores water and water-soluble nutrients in vascular plants. Phloem is responsible for transporting sugars, proteins and other organic molecules in plants. Some diseases plug the entire flow or partial flow which can choke the life out of the tree. This happens in liveoaks with oak wilt, oak decline or sudden oak death in our post oaks. Another great example of interruption in the flow is what we talked about last month, Hypoxylon canker. If you have not read that article in the Wise County Messenger, you should do so. 

Insects on the other hand do not stop the flow but they can transmit and infect the vascular tissues with lethal viruses and bacterial pathogens. With several consecutive years of harsh weather conditions throughout Texas, including extended hard freezes, droughts and heatwaves, North Texas trees have become vulnerable to secondary threats. And we have seen this play out to a larger degree over the last few years. These threats — mainly for cedar, spruce and pine trees — include bark beetles or borers, cedar or pine needle blights and rust fungi. Also there are Ips engraver beetles and others, many types of borers, and of course the deadly fungus like Hypoxylon canker have brought forth significant mortality to mainly our post oak trees. Red oaks and other types are not immune from attack. 

Many trees in Wise County are dying from insects and disease that was exacerbated by extreme weather conditions.

Trees experience threats like insects and diseases regularly, and when a healthy tree encounters these stressors under positive conditions, they can show little to no negative reaction to the threat. However, environmental conditions such as droughts, extreme winter weather and new construction development close to the tree can add primary stress. 

As the trees encounter prolonged stress under these factors, they become more susceptible to secondary threats.  For example, we are still experiencing stressors from the severe droughts of 2011 and 2014-15 as they are still oppressing the surviving trees today.  Experts say that our trees are under such severe stress that it takes one little additional factor like a cedar bark or pine beetle to push the tree into mortality.  I can give a witness to that as I receive many calls each week about dead trees. Cindy and I are also victims and have lost many of our big, tall pine trees as well as many Post Oak trees on our property. I was doctoring them with everything under the sun, but nothing worked. I believe the experts are correct, there is no cure for Hypoxylon canker, and that’s a fact. And once you see beetles, it’s too late to treat. There is usually no hope for the pine or cedar trees survival. Symptoms of beetles in pine trees include discolored crowns, dying branches and numerous white-to-reddish brown pitch tubes on the bark. Symptoms of cedar bark beetles occur in cypress and juniper trees and include the discoloration and dropping of leaves; twig and branch decline; and small exit holes present on the bark of trunk or limbs which are sometimes accompanied by “sawdust” around the boring or tree. Adult cedar bark beetles are approximately the size of a grain of rice with cylindrical bodies and a reddish colored back.  

Management tips

Insecticides are used as drenching preventive sprays on the trunks and larger branches. These insecticides need to be applied prior to adult beetle infestation. (Remember that overwintering beetles begin emerging in spring as soon as daytime temperatures consistently reach 50-60 degrees.) However, timing can be difficult to determine since bark beetles can have multiple, overlapping generations and life cycles. Adults have been observed entering trees during warm days as early as late-February on through November. Because of this extended activity, two treatments (early spring and summer) may be needed to protect trees during high-risk conditions. Insecticides used to prevent bark beetles include either permethrin, bifenthrin, or carbaryl (Sevin) as the active ingredient. 

There are many products currently on the market containing these active ingredients. Follow the manufacturer’s recommendation for the proper rate for bark beetle treatment. Bark beetle applications at the labeled rate should provide at least three months control of these beetles. When a preventively sprayed tree later dies of beetle attack, it is usually for one of the following reasons: 1) the tree was sprayed after it was attacked; 2) the spray was applied at too diluted: 3) the entire bark surface of the susceptible part of the tree was not sprayed; or 4) the material wore off and was no longer effective. I am by no means endorsing or promoting any of these products mentioned here, but I want you to know about them so you can make an informed decision. There is Bio Advanced Tree and Shrub Protect and Feed. It comes in granular or liquid form and the granular is easiest to apply but seems to be more expensive than the liquid used as a drench around your tree. Besides feeding your tree It also provides season long control so do it in the early spring and forget about it until fall, unless you see a problem appear before then. There are other similar products you can use too that are Systemic Tree & Shrub Insect Drench and granules with most of them having the same active ingredient of imidacloprid at different percentages which protects plants for 12 months, and the solution is absorbed through the roots, so protection won’t wash off due to rain or regular watering. Another product with the same ingredient is Merit which also comes in granules or liquid. Any product with the active ingredient of Imidacloprid is great treatment but be aware that it can and will kill honey bees, especially if sprayed on blooming plants. That is what I like about these systemic insecticides you can put in the soil and then it is taken up through the roots for less exposure. 

If you have any questions please be sure and contact me or visit our website at wise.agrilife.org.