For Release May 20, 2003
Why Are The Leaves Falling Off My Tree?
by Chuck Otte, Geary County Extension Agent
A few homeowners have started to notice leaves falling off their trees and this has prompted a few phone calls. Yes, there are problems that are causing leaves to disappear on many trees. It is going to get worse before it gets better. But virtually all of these are relatively minor problems that you don't really need to worry too much about. Let's examine some of the more common ones.
Hackberries - There are a couple of insect pests working on hackberry trees right now. By far the most obvious problem in town is the Hackberry Psylid or Hackberry Nipplegall Maker. Anyone who has a hackberry tree has seen the little bumps on the leaves. This is evidence of the larval psylid. This small cicada cousin overwintered as an adult. In early April they came out of hibernation. As the new leaves broke bud on the hackberries, the psylids laid eggs on them. The eggs hatch, the psylid larva burrow under the leaf surface and start feeding.
There was a very large overwintering population and these adults laid a lot of eggs. The adults have finished laying eggs, but some trees are very heavily infested with larva. The heavily infested leaves go into the human equivalence of shock and the tree starts shedding the leaves. If you pick up some of these leaves, you will often find many little bumps on them. Since the eggs were laid weeks ago, and the larva are completely enclosed in the leaf, it will do no good to spray now. The trees will put out new leaves and will recover just fine.
If you get out into the timber and start looking at hackberries, you are likely to find the leaves being consumed rapidly. The hackberry butterfly caterpillar is very active right now. These trees will be completely stripped of leaves and a second generation may do a little bit of damage as well. Spraying usually isn't practical because by the time you notice them, they have done most of their feeding. The next generation may very well not be as bad because beneficial insects will have built up to help control them. The trees will re-leaf and have the rest of the summer to recover.
Anthracnose - There is a broad range of related leaf disease of trees collectively known as anthracnose. Anthracnose infects tree leaves as they break bud in the spring and start growing. The disease is favored by cool damp weather, which we've had several wonderful periods of this spring. There are several other foliar diseases, such as leaf blister, that we can include in this discussion. The most commonly infected trees include: sycamore, ash, maple, walnut, and elm.
You will usually realize your tree has a problem when it starts shedding leaves about this time of year. When you pick up the leaves you notice all sorts of spots, blotches, blisters or dead spots on them. The infection occurred weeks ago. Spraying now is of very little use. Leaves will continue to fall off for another few weeks, new leaves will come out, and the tree will recover.
Symptoms of potentially more serious damage that you may want me to come look at are quite different. Look for entire branches, or sections of trees, where leaves turn yellow or brown and die, often without falling off the tree. This branch flagging is often a serious situation that needs to be investigated. But leaves with blotches falling off of the tree are just a symptom of a wet spring and the tree should be fine!
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