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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog

Tree Diseases


University of Illinois Extension Horticulture Educator Rhonda Ferree reports that thiss seems to be the year of tree diseases. "Now don't be alarmed," says Ferree, "I've seen a lot of diseases on trees this year, but happily most of them are not devastating."

The reason for the increase in tree disease this year is weather. Spring weather conditions this year were perfect for many tree diseases to develop. Many plant diseases prefer wet spring conditions, which we had. In addition, the odd weather patterns the last couple of years have left many trees stressed and less able to fight off pest infestations.

Some of the diseases Ferree saw this spring and early summer include anthracnose, plum pockets or peach leaf curl, fire blight, cedar-apple rust, and apple scab.

"Anthracnose can attack many trees, but is most common on sycamore." This year it has also attacked many oaks leaving some tree owners thinking their trees are dying. Actually, Ferree says that the trees are just fine, and in fact most sent out new leaves already this summer.

"Plum pockets and peach leaf curl cause leaves to pucker and curl, looking thick and discolored." They may turn brown and fall from the tree. New shoots become stunted and swollen and fruit may be swollen, deformed, and even hollow. Although this disease is easy to control, now is the wrong time to spray. Ferree recommends keeping the tree healthy with proper water and fertilize. "If you use chemicals, follow a scheduled spray schedule next year to prevent this disease."

"Cedar-apple rust and apple scab cause unsightly spots on the leaves of apples (including susceptible ornamental crabapples)." If severe "enough, the spots can entirely cover the leaves, causing the leaves to fall from the tree." The best way to control these diseases is to plant a resistant variety. Otherwise, use good sanitation and rake up all fallen leaves and debris to remove the fungus. Sprays are done early next spring, but timing is difficult.

Ferree reports that Unviersity of Illinois Exetnsion Master Gardener Plant Detectives have fielded numerous fireblight calls this year. Fireblight is the most common and destructive bacterial disease of apples and pears (including ornamental pears). The disease is so named because infected leaves on very susceptible trees will suddenly turn brown or black, appearing as though they had been scorched by fire. The end of the branch may bend over, resembling a shepherd's crook or an upside down "J".

Fireblight is one of the most difficult diseases of apple and pear to control, and there is no one procedure that will give complete control. "We are long past the time when chemical sprays would help," says Ferree. "We recommend removing blighted branches as they occur." "Preferably, this should be done in dry weather and tissue removed from the site." "Remember to disinfect pruners before every cut and to make cuts 10 inches beyond the blighted area." "Do not fertilize infected plants now." "That would encourage succulent new growth, which is susceptible to infection."

For more information on this or other horticultural issues, contact your local Extension office by visiting www.extension.illinois.edu. You can also post questions on Rhonda's facebook page at www.facebook.com/ferree.horticulture.



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