Jennifer, take a close look at the fallen leaves. Do you see orange blisters on the leaves or petioles (leaf stems)? Or do you see any distinct dark patches on recently fallen leaves?
There are 2 fungus diseases that commonly affect ash trees. Both infect the leaves in the spring just after the leaves emerge from the buds, if weather conditions are right. Ash rust disease causes the orange blisters to form. They can be on the leaflets, the petioles and sometimes even on new green twigs. The blisters contain the spores that enable to fungus to reproduce itself. Rust diseasees are unique in that they must alternate between 2 different host species. In this case, the alternate is certain types of marsh grasses. The fungus spreads from the grass to the tree, then back to grass. It cannot go from tree to tree.
The other infection is called ash anthracnose. It also infects in the spring, causing parts of the leaf to appear water-soaked and dark. The fungus can grow down the petiole, sometimes invading the twigs. When the petiole is infected, the whole leaf diesa dn falls from the tree.
Neither disease is usually fatal for the tree. If the tree is otherwise healthy, and hasn’t been severely defoliated in recent years, it will probably put out a second set of leaves in a few weeks. This set of leaves are likely to be smaller, perhaps fewer than normal, but suffice to keep the tree alive. Chemical controls and sprays can be applied as preventive measures by spraying 3 or 4 times, starting when the buds first break open. Spraying after infection is not effective.
Watch your trees for a month or two before deciding on their fate. They may start to show signs of setting new leaves. Keep the trees watered if you don’t get a good rain each week. One watering a week, to moisten the soil at least 4 to 6 inches deep. If possible, spread mulch out as far from the base as possible, keeping it 3 inches deep, maximum, and NOT placed agasint the bark of the trunk.
Two other things to do- contact your local Cooperative
Extension office (blue pages) for confirmation and advice, and find a Certified Arborist on the International Society of Arboriculture web site. (Follow links to ‘Find a Certified Arborist.)
Russ Carlson, RCA, BCMA
Does this also affect hackberry trees? We live in Minnesota and the leaves have been falling off for about two weeks. There's still plenty of leaves on the trees. I don't see any bare spots.
Hackberries have a whole set of their own problems. They commonly have hackberry leaf gall, a small wasp that causes spike-like galls to form, usually on the lower leaf surface. Aphids are also rather common. Both can cause the leaves to roll or distort, possibly to drop off the twigs. While control measures are available, they are often not recommended. These problems can be unsightly, but not usually a threat to the tree’s health.
Find a good local ISA Certified Arborist to check it out for you, to be sure this is what you are seeing.
Www.isa-arbor.org Follow links to Find a Certified Arborist.
Russ Carlson, RCA, BCMA
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