Question of the Week — Why Are Tree Leaves Dropping So Early?

September 7, 2012 | By | Comments (8)
Sugar Maple Leaves

Sugar maple leaves messing up Grumpy’s lawn; Photo by Steve Bender

It may be September, but it isn’t fall yet. So why are some of your trees already dropping leaves? There are three main reasons. Let’s discuss each scenario from no problem to minor problem to major, big-honking problem. 

Tulip poplar

Tulip poplar leaf. Photo by Dendroica caerulea.

No Problem — It’s the Weather

Shade trees typically grow lots of leaves when the weather is pleasantly warm and they’re getting plenty of rain to keep the juices flowing. But growing lots of leaves puts a huge burden on a big tree that can be hard to maintain.

So when the weather gets really hot and dry in summer, the tree responds by dropping some leaves. The tree figures autumn  will soon be here anyway, so what’s the big deal? Tulip poplar (Liriodendron tulipifera) is notorious for doing this. But the good news is it doesn’t hurt the tree.

Minor Problem — Fungus or Bug

Crepe myrtle leaf spot

Crepe myrtle leaf spot. Photo by northescambia.com.

Some trees tend to get leaf fungus in late summer that leads to leaf drop. Grumpy thinks part of the reason is that the tree just gets tired of using its natural chemical defenses. For example, every August and September, no matter how wet or dry the weather, my ‘Sioux’ crepe myrtle gets leaf spot. One by one, the leaves turn red and drop, until the tree stands nearly naked  with pink blooms still on the top. It’s gotten too big to spray with fungicide, but since this annual leaf drop doesn’t hurt the tree’s health, I don’t care.

The leaf drop culprit could also be an insect. In the case of my sugar maple pictured at top, the little jerk responsible is a bug called the maple petiole borer. This tiny sawfly lays an egg in the base of the leaf stem, called the petiole. A larva hatches out and burrows into the petiole, interfering with the transport of water and nutrients. Leaves often drop off green. Fortunately, not enough leaves fall to hurt the tree, so I don’t spray.

Major Big-Honking Problem — Sudden, Total Leaf Drop
One day in early September, your oak tree looks fine. Suddenly, the leaves turn light green, then yellowish, then brown, and then they all fall off. This might by OK in Montana, where fall comes early, but not in the South. While there is a slim chance your tree will leaf out again next spring, if it’s brown or naked while all the trees around it are still green, chances are it just croaked. If it doesn’t leaf out next spring, cut it down. No tree skips a year of growth. No way, no how.

COMMENTS

  1. Steve Bender

    Allene,

    Your sycamore has a disease called anthracnose that causes brown spots and patches on the leaves. Rainy springs encourage it and severe cases can defoliate the tree. You can spray healthy foliage in spring with a fungicide Daconil, but because sycamores grow so big, you’d need a professional tree company. Here is a link with more info on control.

    http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/sycamore-anthracnose.aspx

    June 30, 2014 at 2:46 pm
  2. allene conner

    THE LAST 3 YEARS MY SYCAMORE TREE LEAVES FALL IN LATE JUNE EARLY JULY,
    BY AUGUST IT’S BARE! THE NEXT YEAR IT BLOOM AGAIN AND FALL OFF EARLY
    AGAIN. WHAT CAN I DO?

    June 26, 2014 at 7:55 pm
  3. Judy Schell

    My crytomeria japonica, while growing taller, is not filling out with branches. The landscaper allowed more than 9 ft. between and the tag shows lush trees. They were replaced once but the second planting doesn’t look much better. Whats going on?

    September 15, 2012 at 5:53 am
  4. Steve Bender

    Ellie,
    Just keeping it real. Keeping it real.

    Dianne,
    Can’t tell you how stupid it will look, but two of five trunks can definitely die.

    September 10, 2012 at 2:42 pm
  5. Dianne

    Ornamental “White Spire” birch in SE Missouri front yard with five trunks. Can two trunks die and the others be okay? How stupid will this look?

    September 8, 2012 at 11:07 am
  6. Ellie Long

    Greetings Grump, from 103 degree North Louisiana!!
    I thoroughly enjoy your folksie manner and frankness about my favorite past time; gardening. When you bluntly say ” hey, if it croacked – it croaked” I love that. You don’t tell me to mix some concoction and spray it, or pray over it…geez you just give me a grip on reality so I can move on to another issue on this acre that the sun has baked to a crisp. :) Oh fall – oh fall where for art thou! ~e

    September 7, 2012 at 2:21 pm
  7. Steve Bender

    Holly,
    Early leaf drop is very common with Yoshino cherries and doesn’t seem to hurt them one bit. A couple of cherries near our SL building are completely nekkid right now. But in other years, they hold on to their leaves, which turn nice red and yellow colors. Who knows?

    September 7, 2012 at 12:57 pm
  8. Holly Hamilton

    The yoshino cherry trees here, in my yard and around about, all lose their leaves the earliest. My two are nearly bare already but they do this every year. One of the trees has been in the ground for over ten years and is seemingly thriving. I prefer this to those beech trees!

    September 7, 2012 at 7:37 am

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