Extension Educator, Horticulture
I have great respect for trees. They have a tenacity to continue to live and even thrive under less than ideal conditions. They suffer the slings and arrows of outrageous people–baseball bats, garage sale flyers, and the occasional misguided car. Trees also have their share of diseases. Fortunately some are not as serious as they appear.
Each year we see some spotting and browning of leaves, buds and sometimes stems of ash, maple, oak, elm, walnut and other tree species. Often the cause is a fungal disease called anthracnose. It attacks developing leaves during cool wet weather.
Sycamore have succumbed once again to anthracnose fungal disease. According to Nancy Pataky at the U of I Plant Clinic sycamores are experiencing their usual bout of anthracnose this year. The fungus can kill the first set of leaves so sycamores appear to leaf out late. Fortunately sycamores will produce another set of leaves. Even though sycamores seem to get anthracnose to some degree each year, they continue to thrive.
Anthracnose can also infect ash trees. Often ash trees appear healthy but not as full of leaves, or it can cause the first set of leaves to drop. 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. Another oak leaf problem, oak tatters or "bare bones" has also been seen at the plant clinic recently. On the leaves only the veins and a bit of the leaf blade around the veins is present. The edges are often brown or thickened. The leaves appear to have been attacked by zillions of hungry insects. The cause of oak tatters is not certain, but appears to be the result of cold injury when leaves were in bud.
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. 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 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. For antrhacnose and oak blister, fungicide sprays are not effective once symptoms appear. In addition both diseases are not life threatening. The bottom line is the infected trees will probably outlive us all despite their not-so-perfect leaves.
Mahomet Garden Walk
Sunday, June 27, 11am-5pm
Tour six beautiful Mahomet area gardens. Tickets are $5 advanced purchase or $6 on walk day. Tickets available from downtown Mahomet merchants. Tickets available on tour day at Mourning Dove Farms in Mahomet.