For Release May 28, 2006

It's Spring. Why Are Leaves Falling Off my Tree Now?

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

We all know that trees grow leaves in the spring and those leaves drop off in the fall. So why are trees shedding leaves right now, just a few weeks after they grew them? There are several reasons why trees are shedding leaves right now. A lot of those reasons go right back to the weather and to be quite honest, the problem is going to get worse before it gets better!

For a disease to get started on a tree we need three things: a source of the infection, a susceptible host and the right weather conditions. We had all three of these items in late April and early May. Most tree diseases, at least diseases that attack the foliage, prefer moist conditions. Temperature can be a factor but as long as the daily high temperatures are between 50 and 90 degrees, most diseases can survive and multiply. We had daily highs in the 60s and 70s which was almost ideal for many leaf diseases, and it was cloudy and showery.

Leaf diseases are actually quite common in our area, I see them every year. How severe the diseases become depends, of course, on the weather. Last year we had hot and dry conditions during the critical period so infection was much lower than normal. This year it was cool and moist and we are seeing a lot of diseases.

Most notable right now is anthracnose in sycamore trees. While it sounds very similar to the ominous anthrax disease of mammals, the two are in no way related! Anthracnose overwinters on twigs of sycamore trees and attacks newly developing leaves. The disease infects the leaf and the petiole, which is the little stem that attaches the leaf to the tree. If you find leaves that have recently fallen off a sycamore it is fairly easy to find this canker or dead spot on the petiole and you may even find some little black specks which are just the disease doing its life cycle. You may also notice a whole lot of fuzz on the back of the sycamore leaf. This is normal for sycamore leaves and is nothing unusual.

The bad news is that in a year like this, you may lose anywhere from 50% to 90% of the leaves on your sycamore. The good news is that the disease will not kill the tree. The tree will start to put out new leaves in just a few weeks time and these leaves should be disease free. If the weather stays hot and dry, place a hose under the tree, halfway between the trunk and the drip line, and let it run at a slow trickle for a day. Doing this once every two to three weeks will help the tree recover.

Do not apply any fungicides to the tree at this time. The infection period was weeks ago and it is unlikely that we are going to have additional infection with the weather we are having. Do not let anyone talk you into hiring them to spray your trees. The trees are not going to die!

Sycamores are probably just the tip of the iceberg. We can see anthracnose in walnuts, elms, oaks, maples and poplars as well. I expect those problems to start showing up before long also. The same diagnosis holds for these species as well. Rake up the falling leaves and dispose of them, but don't spray.

We are also going to see trees shedding leaves just because it has turned off so hot and dry so fast. The tree is simply shedding excess leaves that it put on back in those nice growing conditions we had at the start of the month. The best thing you can do, if it stays dry, is to water the trees periodically as I described above. You don't need to use a deep root waterer, just an open hose running at a slow trickle placed half way between the trunk and the drip line!

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