Is it normal for my tree's leaves to fall off the tree during the summer?

I might differ from other horticulturists and arborists on this point. It is not normal or beneficial, from a plant physiology standpoint, for a single leaf to fall or be cut out of a tree before its normal leaf drop (this does not mean they should never be pruned: more on this in another post). Therefore, if leaves are falling off of your tree, as in the case of the river birch in the youtube video below, during August, then some stress factor is acting upon the tree to cause the leaf drop. This could be drought, overwatering, nutrient deficiency, leaf spot disease, insect or mite damage, wind damage, or any of a number of other factors.

In the case of the river birch below, the homeowner asked me if August leaf drop was normal and I of course said no. I was showing her the stippling on the senescent foliage--this was October 9th 2010, still a little early for river birches to be defoliating--and found the mites and leafhoppers. Hope you enjoy!



One further note regarding premature defoliation: I have a good friend and colleague, Manuel Flores, whom I haven't seen or spoken with in a couple of years. Once at a Q&A Manuel says premature defoliation happens because the tree doesn't need the leaves anymore. According to his thesis, the trees need a greater total square footage of photosynthetic leaf surface during the spring. Once they get over this, they dump the excess foliage. I would politely counter that this is incorrect. This thesis does not explain why we can successfully reduce the incidence of premature defoliation by using foliar fungicide applications in the spring, when leaf spot diseases infect the newly emerging foliage. Also, trees that are treated for mites, chewing caterpillars, lacebugs, aphids, scale and other sucking insects, also have lower rates of premature defoliation. Generally speaking, organisms do not voluntarily cut off their food sources, and in the simplest of terms, a leaf is a plant's food source.

Please feel free to leave a comment or send an email. If you're looking for a TCIA Accredited Houston Tree Service or Certified Arborist, call the company I've worked for since 2002, Bartlett Tree Experts, at 713-692-6371. This is my personal blog--it is not affiliated with Bartlett Tree Experts.