North Texas shade trees might be at risk of ‘sudden limb drop.’ What you need to know

Until you’ve experienced it you really don’t think it’s going to happen to a tree you’ve been nurturing and loving for 46 years.

We have a Shumard red oak along our driveway. We live on rural acreage and luckily this particular tree isn’t especially close to our house. At no time have I ever been more grateful than a couple of weeks ago when I went out to walk Zeus the dog to find a huge branch down across our driveway.

The branch was 10 or 12 inches in diameter, and as we walked up the hill, I could see that it had come down from a height of 30 feet or more leaving a jagged stub three feet long still attached to the trunk. I looked closely at the ragged end of the branch there on the ground in front of me and I could see no signs of decay or prior cracking. I had no explanation.

It was a Sunday filled with radio, then church, so we drove out the other side of the drive and I made mental note to check in with Steve Houser, longtime friend from Arborilogical Services of DFW. Steve is highly respected in his industry and was one of the very first people named Texas arborist of the year for the state of Texas when that award was first given by the International Society of Arboriculture more than 20 years ago. In full disclosure, his firm has been an advertiser on my program and in my newsletter for many years.

Steve immediately referred to “sudden limb drop” as a known phenomenon. Mine was obviously not the first call he’d had on the subject. I’ve spent a good bit of time researching it since, and I’m going to give you a summation of theories and facts I’ve discovered, not to scare you, but more to make you aware so that hopefully you won’t encounter it in a bad way.

What you need to know about sudden limb drop:

• It is not common and should not frighten you. Instead, it should merely make you aware of the trees in your surroundings so that you will stay vigilant in their care.

• It can happen to almost any species, but it seems more predominant in oaks, elms, sycamores, maples, and two types that aren’t seen in DFW: eucalyptus and beech.

• It is most common in mature trees whose growth has slowed. It is less common in young, vigorously growing trees.

• Sudden limb drop usually happens in summer. In fact, it is often referred to as “summer limb drop” or “summer branch drop.”

• It is not associated with storms or wind. In fact, our large branch came down on a perfectly still summer night.

• There are theories out there that moisture levels in the interior wood of a tree branch increase at night during hot, dry summer weather. Sudden limb drop seems most common following rain showers that come after periods of extended hot, dry weather. If that’s the case, we may be set up for a real outbreak this year.

• When a branch breaks due to sudden limb drop it is often accompanied by an explosive sound, not a creaking and snapping sound like you might expect. The break may occur two or three feet from the trunk, but it’s not uncommon for it to be 10 or 12 feet out.

• Once a tree has exhibited sudden limb drop it is much more likely to suffer loss of another branch (or more). In fact, our tree lost another long limb four inches in diameter and 20 feet long just a few days later.

• The tree-care professionals recommend that you have an ISA certified arborist inspect your tree as soon as possible if you have a limb come down due to this syndrome. I’ve already scheduled a visit from our tree-care team, and I’ve been told they’ll be looking for limbs that are in any way compromised and that they also will be taking weight off the ends of remaining branches.

• They will clean up the jagged ends of the broken branches to ensure that they can heal properly without decay.

• There is one remaining very large branch on the same side of the red oak’s trunk. It is overhanging a 30-year-old Chinquapin oak as well as a 40-year-old Glendora White crape myrtle, a pride and joy in the Sperry landscape. I’m on the verge of asking the arborists to remove that branch since it would destroy both of those trees should it break and fall.

• Similarly, we have a very large pecan limb overhanging our house. That tree is the largest tree on our 11 acres, and the branch extends out 40 or 50 feet over my home office. I notice that it dips very low after rains or even when humidity is high. Those are very concerning to me. Pecan trees don’t appear on any of the lists I see in write-ups about sudden limb drop, but since pecan wood is notoriously brittle, I’m more than a little concerned.

In summation, the most important thing you can do is to take the best care possible of your shade trees. Watch them closely, and if you see anything that looks off-course, have an ISA certified arborist look at them sooner rather than later. I would suggest you take care of this yet this fall before the trees lose their leaves.