Extension Educator, Horticulture
If you look out over the top of a forest around here you are sure to see a few trees with just a fringe of green leaves on top. The rest of the branches appear dismally naked. It's a quick identification feature for sycamores. Each year they get the fungal disease anthracnose to some degree. It is however worse in years when we have cool wet springs. So you guessed it, sycamore — or maybe it should be "sickagain" — have succumbed once again to anthracnose.
The fungus can kill the first set of leaves so sycamores appear to leaf out late. It can also cause stem cankers that result in branch dieback. In addition ash, maple, oak, birch, dogwood, and walnut are also frequently seen with some spotting and browning of leaves, buds and sometimes stems due to anthracnose. Other tree species are affected less frequently.
Anthracnose can be fairly severe in ash trees. Often ash appear healthy but not as full of leaves or more dramatically it can cause the first set of leaves to drop. Ash can get a more serious disease called ash yellows so check the branches for life.
To determine if branches have the ability to leaf out again, look for live buds on the twigs. Live buds should appear green and plump. Also try scratching the new growth. It should look green and moist. If the buds and branches are dead, the tree may have a more serious problem.
Oaks can also get a fungal disease called oak leaf blister. The leaves are distorted and blister-like growths appear on the leaves. The leaves often appear thickened and almost crisp. Leaves turn downward and inward and may become red or purple.
Keep in mind not all problems with trees are caused by infectious diseases or insects. When new leaves are damaged by cold and high wind, they can appear to be suffering from insect damage. Late frost damage usually appears on the tops of the trees where anthracnose appears in the lower canopy. With weather-damaged leaves, there is no pattern to the damage and the holes in the leaves are jagged. Leaves with wind damage may also have straight-line rips in the tissue. If leaves are damaged while still in the bud, a uniform pattern may appear as they unfurl. Maples often show a great deal of leaf tatter.
If you are not sure the cause of the problem, samples can be taken to the U of I Plant Clinic 1401 St Mary's Road Urbana 61802 ($12.50 fee) or to nearest U of I Extension Master Gardener office.
Generally the best management option is to promote good tree health; water during drought periods, remove dead or dying branches and fertilize if necessary in fall. Try to open the tree to better air movement. For anthracnose and oak blister fungicide sprays are not effective once symptoms appear. Fungicides for the most part prevent infection so they have to be applied before infection occurs. In addition, both diseases are generally not life threatening.
The bottom line is the infected trees will probably outlive us all despite their not-so-perfect leaves.
Tree Walk Saturday June 15 at 10:00 am. Join Bill VanderWeit, City Forester for the City of Champaign and author of the new tree walk guide. Walk will start on the corner of Victor and University Avenue in Champaign.
University of Illinois Extension Master Gardeners Garden Walk Sunday June 16 from 10-5, rain or shine. Tickets are $8 in advance and $10 on the day of the walk at the Idea Garden. Also in Champaign at the University of Illinois Extension office at 801 North Country Fair Drive (217) 333-7672 and local garden centers.