Older, less vigorous trees seem to be more prone to this problem. While some limbs that drop show evidence of wounds or decay, many of these failed limbs appear to be quite sound. The branches that break are usually long and horizontal, as opposed to upright, frequently extending to or beyond the average tree canopy. Unlike most breaks due to wind, which occur where a branch attaches to the trunk, a break due to summer branch drop usually occurs 3 to 12 feet away from the trunk, along the length of the branch. Summer branch drop is not related to wind and often occurs in the afternoon on hot, calm days. Richard Harris, Professor of Landscape Horticulture at UC Davis, published an article on the topic in the Journal of Arboriculture in April 1983 describing this condition and its possible causes, and suggested steps that tree owners can take to reduce the hazard of summer branch drop. Although this phenomenon is not limited to oaks, the sheer size of their branches makes summer branch drop (also known as “sudden limb failure”) in oaks much more hazardous for life and property than branch drop by other tree species. Please share this newsletter with everyone in your address book and all of your friends on Facebook and Twitter to help me spread the word on organics.Summer Branch Drop by JRAAt this time of the year, it is not uncommon for large branches to suddenly drop from oak trees without warning. Listen on the internet or find a station in your area. If you have any questions on this newsletter or any other topic, tune in Sunday 8 am -11 am (CST) to the Dirt Doctor Radio Show. Here is a link on more information on this tree quirk. Remember it is better to water less often for long durations to help promote deep healthy root systems.
On the other hand, light frequent watering cycles over a long period of time weakens trees by promoting shallow, weak root systems. Stress in trees caused by improper watering (primarily over watering) is very common. Surprisingly, proper watering is the biggest challenge. Timely plant health care: organic fertilization, soil aeration, and insect/disease prevention and control.
Quality pruning that avoids flush cuts and excessive thinning.ģ. Properly exposed trunk flares (also known as root flares).Ģ. To reduce the risks associated with sudden limb drop, arborists and tree owners should consider the following preventative measures:ġ. Trees reported to be susceptible to summer limb drop include but are apparently not limited to: oak, poplar, willow, elm, chestnut, chinkapin, beech, ash, eucalyptus, pine, cedar, sycamore, tree of heaven and others. Trees are living organisms and they may fail in ways we’ll never fully understand. What can you do? Neither homeowners nor arborists can easily detect conditions that lead to structural failures, and no one can guarantee that a tree will not fail. This imbalance causes the tree to abort limbs. We agree with the theories that this is a tree’s response to a situation where the demands for transpiration exceed the capacity of the vascular system of the tree. Most often these failures occur on hot still days with no wind. The limbs usually extend beyond the main canopy of the tree. Trees with limbs that fit the profile for sudden limb drop are usually mature with limbs that are very large and horizontal with an upsweep toward the end. But, there are still no definite answers. Some theories about the cause include change in branch movement, tissue shrinkage, internal cracks, moisture changes, ethylene gas released inside of branches and microscopic changes in cell wall structure.
Numerous arborists have looked closely at affected trees to find some visual clues that will explain the causes, but consistent warning signs have not yet appeared. Sudden limb drop has been reported in many countries and related to many tree species. Failed limbs usually reveal no obvious external defects and the inner wood is broken bluntly, with no sharp splintering. On windless, hot summer days or evenings, large limbs suddenly and mysteriously break with a loud "crack" and crash to the ground. Limbs fail sometimes because of defects and unusually heavy loads of foliage, but there is another kind of failure known by one of these three terms "summer limb drop," "high temperature limb drop" and "sudden branch drop." It seems to occur when trees are struggling to balance the water coming in and leaving the plant through transpiration.
Here’s an update for you on a previous report we did. It may be happening more than normal this year because of the cool/hot/cool/hot weather.
I’m getting calls from several parts of our area and other parts of the country about this common summer phenomenon.