Extension Educator, Horticulture
Wind, hail, torrential rain, above normal temperatures and below normal temperatures. Trees have endured, or at least hopefully endured, them all this spring. Trees are amazingly resilient. 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 tree leaves. This year it could be from heavy winds and cool weather in the spring. With ash, maple, oak, elm, walnut and sycamore the cause may be a fungal disease called anthracnose. It attacks developing leaves during cool wet weather.
Sick sycamores have succumbed once again to 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. Anthracnose also affects sycamore twigs causing cankers and twig dieback. Even though sycamores seem to get anthracnose to some degree each year, they continue to endure.
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 young growth with your thumbnail. Twigs 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.
Peach trees get a similar fungal disease called peach leaf curl and I have seen plenty of it this spring. The leaf symptoms are similar to those on oak with puckered leaves and red blisters. Infected peach leaves may yellow and drop early in the season. A spray of lime sulfur sold as Bordeaux mixture during the dormant season is the only fungicide spray to control peach leaf curl.
Another oak leaf problem, oak tatters or "bare bones" has also been seen this year. 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, but no insects are visible. The cause of oak tatters appears to be herbicide drift when oak leaves are small but cold injury when leaves were in bud can cause similar symptoms.
Not all tree leaf problems 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. If leaves are damaged while still in the bud, a uniform pattern may appear as they unfurl.
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, IL 61802 217-333-0519 http://web.extension.illinois.edu/plantclinic/ or to nearest UI Extension office. http://web.extension.illinois.edu/state
Generally the best management option is to promote good tree health; water during drought periods; remove dead or dying branches; mulch lightly; and fertilize if necessary in fall. For most fungal leaf diseases such as anthracnose and oak blister, fungicide sprays are not effective once symptoms appear. The bottom line is the infected trees will probably outlive us all despite their not-so-perfect leaves.