Weak branch unions are easy to spot before they become a problem…
Weak branch unions are one of the most common hazards we see on clients’ properties. This hazard is easily identifiable and, thus, easily avoided. But what are the signs that tell us a weak branch union likely exists?
The most frequent weak branch union we see is called a co-dominant stem. This is where two stems of roughly the same size arise from the same point on the tree. (This is also known as a “schoolmarm” in forestry circles…but it’s up to you to learn the backstory on that.) The junctions between co-dominant stems are often considered the weakest portion of a healthy tree. They are widespread in forested areas; you’ll often see them on area trees, especially ponderosas. It will look like the tree has two or more tops. This creates a weak branch union because the two stems, or leaders, are growing so closely together that the bark on each leader interferes with the formation of a proper, strong union. This is called included bark, and it doesn’t have the structural strength of a normal branch crotch. Furthermore, included bark can act as a wedge, forcing the weak branch union to split apart.
Removal of a ponderosa with co-dominant stems earlier this spring. Weak branch unions are especially troubling near structures.
During the windstorms of recent years, we’ve seen countless trees lose one of their co-dominant stems. Wind will point out any weak branch unions you have, if you’d rather not pay a professional to investigate. The problem doesn’t stop with the toppling top of the tree—and subsequent property damage—though. Once one of the co-dominant leaders is gone, a wound remains and leaves the tree structurally weaker and vulnerable to infection. The best approach is to be proactive about trees with co-dominant leaders. Either remove one of the leaders in a controlled environment, or cable the two stems together so they support one another and don’t sway past the trigger point in the wind. We are well versed in both approaches and can talk you through options.
Another example of a weak branch union is when epicormic branches (also known as watersprouts or suckers) are allowed to grow into sizable limbs. Epicormic branches grow quickly—often in response to poor pruning practices, injury or some kind of environmental stress—and they always display weak branch unions. It’s best to tend to suckers when they are newly formed, before they pose any real hazard to structures and people.
Finally, any branch that comes off the trunk at a very acute angle or doesn’t display a ridge of raised bark at the crotch is of potential concern. If you have trees on your property that exhibit any of the signs of a weak branch union, call us for a free consultation and estimate. Considering the widespread impacts of recent windstorms—and the fact that weak branch unions are especially susceptible to failure in wind—a call to us will at least provide peace of mind.
Mistletoe may be good for those desiring a kiss but not so much for your trees…
We see a lot of mistletoe around here. Unfortunately, that doesn’t mean that love and lingering holiday cheer are in the air, but rather, that the seeds propagating the parasite are soon to be airborne. (And watch out: Mistletoe seeds are ejected from the plant at speeds of up to 60 mph!) It’s something to be aware of as mistletoe is detrimental to the health of your trees.
Note the abnormal branch growth of the witches broom on this fir. Photo by Cephas via Wikimedia Commons
North Idaho is home to a handful of dwarf mistletoes that are specific to our native trees. Larch, Douglas fir, ponderosa and lodgepole pines are all primary host species. In our work, we have seen it most often in larch and Douglas fir.
What does mistletoe look like? It’s most easily spotted when the infection is full-blown and affected limbs have witch-broomed in response. A witches broom is a mass of chaotic branch growth that appears as a dense clump in your otherwise well-formed conifer. The witches broom is a response to the mistletoe but not the mistletoe itself.
Larch dwarf mistletoe shoots begin to sprout in the spring eventually forming clusters of shoots as seen in this plant. Photo courtesy of the USDA Forest Service Archive
Mistletoe is hard to detect early on. For several years, no outward symptoms may be apparent. This is known as a latent infection. After several years, though, scaly shoots emerge. However, since they are only two inches tall and are likely hidden in the canopy of the tree, most property owners don’t notice the early stages of mistletoe infection. Thus, we are often called in to treat more heavily infected trees that have had many years to spread the parasite to surrounding trees. This makes mistletoe eradication difficult.
Mistletoe harms trees in numerous ways. For one, as a parasite, it takes water and nutrients from the tree for its own growth, leaving the tree weaker and more susceptible to other insect and fungal invaders. Infected trees grow slowly, and heavy witch-broomed limbs are prone to breakage due to their weight. Mistletoe often leads to tree death. It also creates a fire hazard. All of this means that a mistletoe infested tree is a hazardous tree.
Our approach to mistletoe treatment is to first assess the tree to determine if the tree is a candidate for pruning or removal. If the infection isn’t too severe, pruning of witches brooms and less affected limbs will be undertaken. Healthy looking limbs adjacent to infected ones may also be removed in case infection is latent. Pruning in subsequent years may be necessary to catch future outbreaks. And pruning is best undertaken in the early spring or late fall when pollen and seeds are not being released from the mistletoe. We don’t want to inadvertently spread more infection.
One last thing to consider is that mistletoe does have its uses. Various birds and forest animals use witch-broomed limbs for cover and as nesting sites. We once found ourselves in a tree, dodging a group of flying squirrels leaping to safety. There is something to be said for leaving an infected tree alone if it is not a direct hazard to you and the health of your forest.
If you have concerns about mistletoe, give us a call for an assessment. And for more information, there are several helpful publications online:
