Sometimes after working with old perennial plants and pruning shrubs, I find my hands are covered with gray powder. This powder is fungus spores. At this time of year, it affects many plants, and it is a good thing some frost is on its way.
Healthy, well-tended plants generally are immune to fungi and other diseases, but after a long growing season, they become less able to resist fungi and bacteria. Any small lesion or damage creates a break in the epidermis, and allows infection-causing organisms to penetrate into the body of the plant.
Spotted or blotched leaves with yellow margins around the spot generally indicate disease, and rust also affects foliage. Root diseases are hard to identify, although if a plant's leaves turn brown and die off on parts furthest from the roots, root problems are likely. This may also be caused by stress, soil compaction, excess water or root curling in a pot-bound situation. All this makes it difficult to identify specific diseases, and so it is hard to find effective treatment.
If you grow hollyhocks, you have probably encountered rust. Those brownish red leaf spots are unsightly, but not fatal to a plant. Lower leaves are generally affected, and they wilt and hang down. Rust spreads quickly in warm, wet weather. Picking off blemished leaves can be an endless task, as splashing water and wind spread the spores to healthy plants. Fungicides will help, but it is really a losing battle once the infection sets in. Be sure to remove plants that were rusted when you do the fall clean-up.
Other leaf spots may be caused by a wide range of bacteria, including the ubiquitous black spot on roses. The characteristic spots with irregular edges appear in wet seasons. The fungi spend the winter on infected canes and spread from one plant to another by splashing water. The spots begin as pinhead-sized marks, and enlarge to form blotches in severe cases. There are plenty of sprays on the market to control black spot, but a certain amount of it goes along with growing roses for me, and I just pick off the yellowing leaves and twigs and dispose of them.
Powdery mildew is a nuisance that attacks in dry weather as well in humid conditions, unlike most fungal diseases. The powdery spores attack many different plants in late summer and early fall. I seem to find it first on lilac bushes. Authorities recommend a spray containing triforine to stop the spread of the spore-producing condition, but I find the leaves are beginning to drop anyhow soon after the condition is visible, and that takes care of the problem.
As you see, I don't get too excited about fungal diseases. Just as most children are expected to come down with sore throats, infected ears and snuffly noses in the winter time, so most plants will pick up some blemishing conditions once summer is over. Some parents run to the doctor for antibiotics, while others stoically weather the storm with simpler home remedies, and in the same way some gardeners hit the stores for fungicides while others wait for winter conditions to end the problems.
The children and the plants will survive. Anyone passing my garden at this time of the year had better not look too closely. I am working slowly around the flower beds to cut back and tidy up, and am weeding and digging over the vegetable plots, but things are not tidy or attractive at the moment.
Janet Del Turco is a local gardener and a graduate of the Ohio State University Master Gardener program. Contact her at firstname.lastname@example.org.