Got spots? Yellow, curled, prematurely dying leaves? If the plant is otherwise healthy looking, the culprit is probably leaf spot. Most leaf diseases are caused by fungi, although bacteria and nematodes can create foliar problems too.
Earlier this spring, conditions were ideal for fungal diseases to get a foothold in many gardens. First it was unusally warm, then turned quickly colder with temperatures remaining below normal for several weeks, followed by a period of no rain. Such conditions are optimal for leaf spot.
Here’s what to know and how to control this common, widespread nuisance.
Check your plants. If there are yellowing leaves on the lower quarter of the stems and around the soil line, look closer. Stippled and scattered dark brown spots up to 1/4-inch in diameter, perhaps with a small gray center, is septoria leaf spot. It’s common on both ornamentals and vegetables when spring weather is overly cool.
I have it on my phlox. The plants look very healthy otherwise, although one plant with septoria had weak, floppy stems as well as dying and stippled leaves. I cut all infected stems back to the base. It will regrow and eventually flower, just much later in the season.
After reading up on treatments, the usual recommendation is to remove all affected foliage (but not more than a third per plant) especially dead and yellowing leaves. Don’t compost these; dispose of them in the trash. That may all that’s needed if you caught the situation early and the plant is otherwise doing well. Do prune off weak or poorly growing stems.
If the problem continues or if leaf removal is impractical, apply a fungicide. Read the labels — there are several different types on the market and they don’t all control the same things. For instance, copper-based fungicides are great for black spot may not help with leaf spot.
I use a sulphur dust formulated specifically for organic gardening that treats leaf spot (among other things). Follow directions carefully, and be sure to keep the plant well watered. Hopefully it will recover nicely.
If the weather stays hot and dry, it may return. The best defense is to keep your plants watered, mulched and any diseased foliage removed as soon as you notice it. Leafhoppers and other insects can spread it around the garden in no time if it’s left to proliferate.
If you’ve had good luck with a particular treatment or product, let us know in the comments. Fortunately mild cases of leaf spot doesn’t usually kill the plant, but it does weaken growth and looks awful.
Good luck!
