by Connie Oswald Stofko
“The wetness we had early in the season has caused disease issues that will show up the rest of the season,” said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County.
These issues include mildew and blight.
How you handle it depends on the particular plant that is affected as well as on your gardening preferences.
Some plants that get a fungal disease don’t need to be treated at all. If a lilac bush gets powdery mildew, the leaves will be unattractive now and may drop early, Farfaglia said. Other than that, the disease won’t harm the shrub, which is already done blooming anyway. It will survive and it will bloom again next year.
You may want to use fungicides on plants such as roses. Fungicides are often used to prevent or treat black spot because without treatment, the plant may stop blooming, he said.
But when it comes to vegetables, gardeners may decline to use a fungicide. Many home gardeners grow their own vegetables because they don’t want vegetables that were grown using chemicals, he said, and they accept the bad years with the good years. If you have tomato blight or mildew on squash or cucumbers and don’t want to use a fungicide, you may cut off the diseased parts of the plant, bag them up and throw them away so the disease doesn’t spread.
If you do want to use a fungicide, see the 2015 Vegetable Fungicide Table for Home Gardens from Cornell University.
Keep in mind that before you select any treatment, you should know what is causing the disease. A fungicide is used to kill or inhibit fungus. Mildew is a kind of fungus. Black spot is caused by a fungus. Tomato blight is caused by a fungus.
However, not all blights are caused by a fungus; some blights are caused by bacteria. Fungicides won’t work on bacteria or on problems caused by insects.
A fungicide might work on one fungus but not a different fungus. And not all fungal diseases can be controlled with fungicides.
Besides knowing what to spray, you need to know when to spray. Most fungicides need to be applied before disease occurs or at the first appearance of symptoms to be effective. Sometimes when to spray is as important as what to spray, Farfaglia noted.
With all these variables, how are you supposed to choose a specific course of action?
Go to Cornell Cooperative Extension. They have many factsheets on particular plants as well as diseases associated with that plant. A good place to start is the Plant Disease Diagnostic page and the VegMD Factsheets.
You can also contact the Cornell Cooperative Extension in your county with your questions. You can call or email. The nice thing about emailing is that you can attach photos of your affected plant to help identify the disease.
Emerald ash borer is still with us
While we’re on the subject of diseases and pests, Farfaglia reminds us that the emerald ash borer is still with us. This non-native insect can kill ash trees within two to four years of infestation.
If you have ash trees, you may want to treat them or have them taken down. Contact an arborist to find out what steps you should take.
“Don’t delay,” Farfaglia said. “It’s sad. A lot of trees are going to be lost.”
See a map of quarantine areas here, which include large areas of Western New York.