Oak Tree

(Question)

Our Oak tree has brown edged leaves that curl in on themselves like they are dried out. But they don’t feel dry and crunchy. These leaves are more prevalent on the south side of the tree, the other half of the tree is okay. This is the third year we are seeing this. The leaves start to look brown in Late June to early July. The tree is about 25 years old, with an 8″ diameter trunk. It stands alone about 60′ from the shore of Lake Ontario, in clay soil in the sun.Oak Leaves 20150717

 

(Answer)

Such browning of leaf edges can be caused by lack of water, especially in clay soil, since sun-baked clay soil particles tend to swell when wetted, blocking moisture from reaching the roots. The Ontario Ministry of Agriculture, Food and Rural Affairs suggests that aeration or loosening of the soil well beyond the trunk may help reduce this problem. You can see their web page on this subject here.

However, the fact that these symptoms have appeared repeatedly over three years and that the leaves are not brittle suggests that disease may be a factor. Your photo and description seem to correspond to the symptoms of Bacterial Leaf Scorch (BLS), which is commonly seen in oak trees. In the early stages of the disease, not all parts of the tree are affected, but over time, more branches exhibit typical leaf scorch symptoms.  If you check out the American Phytopathological Society web page, you will find that Figure 11 is very similar to your own photo.

BLS is sometimes mistaken for Oak Wilt. However, Oak Wilt kills the tree within months, whereas BLS can continue for as many as 8 years before the tree loses all its leaves.

If you do not think that drought is the issue, the only way to confirm the existence of BLS is through laboratory testing. As the OMAFRA site explains, samples can be submitted to the Pest Diagnostic Clinic in Guelph. There is a fee for this service.

The Pest Diagnostic Clinic
Laboratory Services Division
University of Guelph
95 Stone Rd. West
Guelph, Ontario. NlH 8J7
Phone: 519-767-6256
Fax: 519-767-6240
E-mail: pdc@lsd.uoguelph.ca
www.labservices.uoguelph.ca/units/pdc/