Question: There is a tree in our yard that has rough warty bark and makes a small fruit about the size of a cherry. The problem is it is dripping a sticky substance on everything underneath its limbs. Do you have any idea what tree this is and what might be the problem?
Answer: The tree is probably a native hackberry or sugarberry tree, but the fuzzy white pest causing the sticky mess is not native. The pest is called the Asian Wooly Hackberry aphid and was first detected in North America on hackberry trees in Georgia in 1996 and in Alabama in 1998. It is not a severe problem every year, but it appears to be a problem this year. The aphid appears to be restricted to native hackberries or their relatives. Although the trees seem to survive the pest flair ups fine, the aphids produce large quantities of the sticky substance called honeydew. As you observed, this creates a sticky mess and promotes the growth of black sooty mold on leaves and on surfaces beneath infested trees. In August and September it can look like a mini snow storm near these trees because the aphids look like cotton fuzz balls. Although this tree is a very tough tree for urban environments, the honeydew can be an annoying problem in residential and business districts where the tree may be used to shade parking lots, walkways or patios.
Some municipalities out west have been treating all hackberry trees in parks and parkway strips with a systemic insecticide called imidacloprid, which is an effective, but relatively expensive insecticide. Researchers at the University of California have had good results with this insecticide even with rates as low as one eighth of the label recommendations. Since it is a fairly expensive product you might try these lower rates and just provide adequate water to make certain what you apply is not wasted. Imidacloprid can provide season long control and can be applied during the growing season after you notice an early infestation in the spring. Treatments are applied as a systemic insecticide, meaning that the product is taken up by the roots of the plant and spreads through all the tissues of the plant. The material may be mixed in a bucket of water and poured around the trunk. It is too late to treat trees now and it won’t be long before the leaves fall off anyway. Just to play it safe don’t use this product near edible plants since it is taken up by plant roots.
The fruit is a favorite fall treat of many birds and other wildlife. This is another reason to use the lowest possible effective rate of insecticides so that the pesticide will be out of the plant by fruiting time. Since there is no research to tell us if the chemical is totally gone by harvest time, I would suggest you avoid eating the fruit.
I talked with the director of the Plant Diagnostic Lab here at the Hanna Environmental Center, Dr. Jim Jacobi and he said “the wooly hackberry aphid does not cause appreciable damage to tree health but from time to time can be quite a nuisance. I would not plant this tree in an area near a parking area or patio, but it can still be used as a specimen tree in a natural area or at the fringes of your property where it won’t cause a mess and can still provide food for wildlife and act as a host plant for at least three species of butterflies that develop on the foliage.”
For more information visit the following web address: http://msucares.com/ and search for Wooly Hackberry Aphid. A great detailed article will be the first link that pops up.
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