These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.
Sick Looking Leaves on Trees
July 8, 1999
Samples from trees make up a large percentage of problems brought into Extension offices in summer. Some problems are due to insects or disease, others are brought on by weather damage, physical injury to the trunk or roots, or other site factors. Here's a sample of some of the more common foliage problems visible now.
Anthracnose, a group of fungal diseases, has been common this year. Cold, wet spring weather as leaves developed on the tree favors anthracnose, which affects a wide variety of trees, including oak, ash, and maple. Typical symptoms on leaves include irregular blotches or dead areas, often curled up. If a tree is infected heavily, considerable leaf drop may occur after leaves emerge, with a second set of leaves often following. New growth is not affected since the weather is warmer and drier.
Anthracnose may look bad, but is not considered life threatening to the tree. Defoliated trees may benefit from fertilizing (this fall) and watering during extended dry periods of summer. Remember roots go as far as the dripline and beyond.
As has been the case the past few seasons, apple scab is common on crabapples. Scab starts as olive to black spots on leaves, with leaves eventually turning yellow or brown and dropping. Severely infected trees may drop about all their leaves over the course of the summer. Defoliated trees will be weaker and more prone to other problems.
Not much can be done right now for scab. Fungicide sprays could be considered for next spring. Also consider replacing scab susceptible trees with resistant cultivars available.
An additional leaf problem we see about every summer is leaf scorch. Leaf scorch is browning of leaf margins, and is not a disease but rather a symptom of some other problem. Scorch means water is being lost from leaves faster than the tree can replace it. Leaf scorch may occur on a healthy tree due to lack of water and lots of wind. Scorch may also be due to an underlying tree problem, such as trunk or root damage, disease, insects, or general poor growing conditions. Scorch may also be common on recently transplanted trees.
So if lots of leaf scorch is showing up on a tree, do some investigating to assure the tree does not have some of these types of problems. Some problems may have solutions, others may not. Trees with lots of scorch may benefit from watering during dry periods.
For more information on tree diseases, see our Focus on Woody Plant Diseases website.