Our winter to spring to summer transition all in the space of two weeks surprised everyone. Our trees are showing the very human characteristics of stress and discomfort.
Sycamores, maples and oaks are having a particularly hard time making this weather change, says Jerry Goodspeed, Utah State University Extension horticulturist. Their major problem is a disease called "anthracnose." The name is actually the scariest thing about this disease. It sounds like a title for a sci-fi movie about a germ that kills off the entire world, but it's really not that bad.
"This disease is present every year, but is particularly noticeable in wet, cool years," Goodspeed says. "The fungus responsible for anthracnose spends the winter on fallen leaves and twigs, or in swollen cankers on the tree. During cool, wet weather these spores that overwintered are blown and splashed up into the tree. They land on unsuspecting buds, leaves and twigs and start growing."
When the weather is wet and cool, infestation of newer twigs and leaves continues until the weather warms and dries out, he says. Conditions can also be aggravated by excess watering with sprinklers, especially if the sprinklers are hitting the foliage.
In the early spring, infested buds and small leaves may turn brown and die, Goodspeed explains. As the leaves expand and grow, the infection becomes evident on the veins that turn brown or black. The rest of the leaf begins to die back, sometimes looking like it has summer scorch or some other die-back. Many of the infested leaves eventually die and fall from the tree, causing many homeowners to think their tree is in serious trouble.
"In severe cases the infection moves from the leaves and buds into twigs, and then to branches," he says. "The infected twigs die and either fall to the ground with the leaves or remain as dead wood in the tree. The infection can move into larger branches causing them to suffer some die-back. In northern Utah, though, it is rare to have major branches or the whole tree die from anthracnose."
In most cases, he says, some leaves and twigs are lost, but the tree remains healthy and recovers once the weather warms and dries. New leaves emerging throughout the summer are rarely infected. By summer's end there is little sign of the damage.
What can you do?
"If the tree is infected, not a lot can be done at this point. Mother Nature is helping by providing hot, dry weather once again. It also helps, as stated earlier, to prevent sprinklers from watering tree foliage. Pick up and remove all fallen leaves and twigs. They contain spores from the disease and, if left on the ground, can reinfect the tree," Goodspeed says.
"Prune out any badly infested twigs and branches, disposing of them along with the leaves. In the fall, rake up and discard the leaves and fallen twigs to reduce the amount of overwintering organisms."
A spray is normally not required for these trees, he says. If a severe infestation has occurred in past years and the trees are weakened, a fungicidal spray can be applied in the early spring, just as the leaves are emerging. Repeat this application about every two weeks until the leaves are fully developed. A fungicide containing the chemical chlorothalonil (an example is Daconil) is probably the best for homeowners. Be sure to read and follow all label directions carefully.
"As for this year, don't worry too much about the trees. Like most of us, they will learn to adapt to the odd weather. They may not like it, but at least they are quiet and don't whine too much," he says.
For more information, contact your local USU County Extension office.
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Issued in furtherance of Cooperative Extension work, Acts of May 9 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Robert L. Gilliland, Vice-President and Director, Cooperative Extension Service, Utah State University, Logan, Utah. (EP/09-98/DF)