For Release June 6, 2000
by Chuck Otte, Geary County Extension Agent
I had a great plan for a series of two columns dealing with pesticide resistance. Then Monday morning arrived and with it three questions on hackberry tree leaf drop in the first 45 minutes. You can read my two pesticide resistance columns in the coming weeks. This week we talk about hackberry trees.
Hackberries are getting hit all over the place right now. We are seeing two basic problems. Problem one is the leaves dropping off the trees and the leaves are covered with lots of little bumps. Problem two is hackberry leaves just disappearing. Weíll take them in order.
Many hackberry trees around town are dropping leaves. These leaves are covered with lots of hard little bumps. Even many of the leaves still on the tree are covered with bumps. These leaves may or may not yet fall off the tree. If you carefully slice open one of these bumps, you will find a tiny little maggot or larvae inside. This is the immature form of an insect called the Hackberry Nipplegall Maker, or Psyllids.
This insect is a type of fly or gnat. If you have been bothered in the late summer with thousands of tiny gnats, or flies, covering your screens and trying to get into your house, these were probably the adult psyllids. In the spring, adult psyllids congregate on newly emerging leaves to mate and lay eggs. If, and thatís a big if, you can spray at this time, you have a chance to reduce the level of infestation. The truth is that this is very difficult to do because the egg laying can extend over several weeks.
The eggs are laid on the leaf surface and the young maggot starts feeding right at the leaf surface. The plant reacts to something in the saliva and grows the gall around the young maggot. Inside this protective gall, the maggot continues to grow until emerging from the gall in the late summer, or early fall as the adult psyllid. While unsightly and a nuisance, the Hackberry Nipplegall Maker does not seriously damage the tree. New leaves will emerge and be uninfected. In periods of heat or drought stress or under heavy infestations, the tree will shed a lot of leaves. Rake them up and dispose of them, and keep the tree well watered to encourage regrowth of leaves. Then prepare for this fall, because we will probably have a large increase in the adult Psyllid population.
In parts of the county, hackberry leaves have just been disappearing. This was caused by the first generation of the Hackberry Butterfly. The early laid eggs hatched and, in many areas along rivers, the hackberry trees were stripped. Now we are seeing thousands of small brownish butterflies in these areas. These will mate and the resulting caterpillars will feed on the reemerging hackberry leaves.
While this damage looks rather devastating, especially in some of the large groves of hackberries, the damage is usually not that bad. I would be more concerned about controlling this second generation than the first generation on landscape trees in your yard. But if you are not seeing the caterpillars feeding on leaves, donít waste your time spraying.
Okay, a quick review. If you have a hackberry tree with lots of leaves falling off and the leaves have little bumps, then you have the Hackberry Nipplegall Maker. Itís a messy nuisance but wonít cause long term problems. If the leaves on your hackberry are not falling off, but just disappearing, you probably have the Hackberry Butterfly. If you are finding lotís of new little green caterpillars on your hackberry, you may spray if you want, but it isnít critical.
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