Post oak trees have been struck by a double whammy of drought and wet summertime conditions that has them dropping in droves statewide, according to local arborists and the Texas A&M AgriLife Research unit.
Though some property owners swear their seemingly healthy post oaks gave up the ghost overnight, the disease process that claimed them likely had been applying a death grip for months, if not years, said Duncan Brooks, a Waco-based arborist who has been diagnosing and treating sick trees for decades.
Trees die all the time for various reasons, but experts say an epidemic is sweeping the post oak population this year.
“Since the early spring to late summer, there have been many inquiries as to why post oaks have ‘suddenly’ died,” Kevin Ong, director of the Texas Plant Diagnostic Lab, said in a press release. “When you get a whole bunch of folks asking the same question, and they are from all over Texas, even in the Panhandle, you know something widespread is up.”
“Leaves start yellowing, may develop spots and ultimately turn brown but still cling to the tree limbs. . . . At that point, the tree is already dead,” the press release states, quoting Sheila McBride, lead diagnostician for the lab.
“We are seeing the symptoms everywhere. It’s in the urban environment. It’s in the rangeland environment. It’s in the woodland environment. It’s not just happening in one spot,” McBride said in the press release.
Local arborists said post oaks thrive on sandy soil and are most abundant locally along riverbanks and in communities such as Robinson, Elm Mott and Chilton.
“Is the Waco area being affected? I would say yes, anywhere in the state that has gone through or is going through broad-scale climactic fluctuations,” said David Appel, Texas A&M AgriLife Research forest pathologist, during an interview this week. “I would expect the problems to continue. . . . Those engaged in research have said it takes six, seven or eight years of normal rainfall for trees to come back.”
In Texas, multiple consecutive years of consistent rainfall is not commonplace, and even back-to-back years often is rare, Appel said.
The National Weather Service reports that Waco received 27.16 inches of rain during all of 2011, slightly more than half the 53.74 inches it received in 2015. Through Wednesday, 35.89 inches of rain had fallen since Jan. 1, which is about 5 inches above the norm of 30.76 inches for that period.
Arborists who spoke to the Tribune-Herald said the drought five years ago may have served as the catalyst for the malady plaguing post oaks this year, but they also blame the unusually wet springs and summers in recent years for feeding a perfect storm that contributed to their demise.
Appel classified the phenomenon as rapid oak decline, though in the AgriLife Research press release, he said “rapid” is in the eye of the beholder. A tree may be developing early symptoms unnoticed long before it collapses, he said.
“The very early symptoms are rather subtle,” Appel said. “You get in your car in the morning or drive by a field, and you don’t notice the trees until the situation is too far gone to reverse.”
Most post oaks at this stage face certain death, though Appel said drastic measures sometimes buy time and a few years of health.
“What we try to do is stimulate the feeder system of trees struggling with stress and which have depleted all the carbohydrates they have stored,” he said. “Vertical mulching involves drilling holes vertically into the soil 2 inches in diameter and 12 to 24 inches in length and filling the holes with composted bark or organic matter. You can end up literally drilling hundreds of holes under the canopy of a tree, and thereby provide an environment to stimulate the feeder root system.”
He said wood-boring insects sometimes inflict the fatal blow by laying their eggs inside the sickly hosts. These must be dealt with quickly.
“Visit the garden center and get some insecticide,” Appel said. “I know some people frown on using that, but you have to remember drastic measures are necessary.”
Appel said he wants to emphasize the recent spate of tree troubles is not at all related to oak wilt.
“We have a perfect storm of environmental conditions,” he said in the press release. “The tree’s physiology is weakened by the drought and weather extremes, and then we get what we call contributors — canker-causing pathogens, root rot pathogens and insect borers. We believe that is what’s really leading the problem with the post oaks.”
Don Williams, owner of Big Country Trees, said he’s made 51,000 on-site inspections of trees in the five decades he has worked seven Central Texas counties, including McLennan. He said what is happening with post oaks is nothing new.
“It’s been going on 20 or 30 years, but people are just now talking about it. . . . Post oak trees are extremely sensitive to environmental changes,” Williams said.
Home and commercial construction, land clearing for farming and the raising of livestock can disrupt the fragile balance that ensures post oaks have enough water, but not too much, and that their fragile root system is not disturbed, he said.
Appel agreed that post oaks have succumbed to weather and man-made conditions for decades, but the mortality rate has been much higher and more widespread in 2016.
“You have to look at what the specific site conditions are,” Appel said in the press release. “In an urban environment, there may be ways to make up for the environmental extremes that have been happening.
“It may be useful to water the trees occasionally but only every three or four weeks at most. . . . A tree should be allowed to dry out very nicely and stay dry, because post oaks hate having wet feet.”
He said next spring, when leaves return to post oaks, is a good time to examine them for signs of danger.