Three of the most common victims are the old-fashioned Lilacs, Monarda (bee-balm), and the tall Phlox that bloom in mid-summer. As fungi go, powdery mildew isn’t terrible: rarely is a plant killed by Powdery mildew.
But we’ve had enough humid weather that some other, more typical fungi, are showing up, too. Several maples in my yard are showing signs of leaf fungus, pictured here in the “frog-eye” stage. Later on, these spots may darken into the “tar spot” phase, as spores develop.
It’s a little alarming when fungal disease hits the garden – your first thought is always, “Where did that come from?” Some fungi arrive on nursery plants: these are often the soil-borne sorts. But many other fungal spores are in the air much of the time, just floating around, looking for a suitable host.
Without fungi, of course, we would be up to our keisters in undecayed vegetation. We can thank fungi and bacteria when our compost piles turn into something wonderful.
Some fungi rely on the alternate host approach – part of their life cycle occurs on one species of plant, and then the spores are transferred, usually by air currents, to a totally different species. A common one around here is the Cedar-Apple rust, which causes bizarre, tropical-looking fruiting bodies in our native Eastern red cedar in early spring, followed by horrible leaf blisters on apples and crabapples, frequently causing defoliation.
Leaf spots are often preventable, but for some of us, the cure is worse than the disease. Fungicides must be applied, in most cases, before the fungus attacks. So, you need to be aware that the disease is coming – not easy unless you’ve lived with a plant for several years, and know what weather will be conducive.
Multiple sprays are needed, since it’s hard to hit every leaf when you spray – not to mention that new leaves will develop regularly on a growing shrub or tree.
One approach that works for some fungi, especially Powdery mildew, is to spray with a solution of water and baking soda. The recipe is: mix one tablespoon of baking soda in a gallon of water, and then add a half teaspoon of liquid soap to help the solution adhere to the leaves. Note that that word is soap, not detergent. Dish “soap” – really detergent – is pretty nasty stuff from a plant’s point of view. You wouldn’t want to drink it, for sure.
As with any foliar spray, this should be applied early in the day, both to give the leaves time to dry in the sun, but also to prevent scorching when the temperature zooms. The first time you use it on a plant, test the spray on just a couple of leaves – like a patch test before coloring your hair. And I know you don’t color your hair – it’s just an example!
One last, all-too-common leaf fungus: black spot on roses.
These are leaves from the white Meidiland ground cover roses – “virtually” guaranteed to be resistant to fungus! Caveat emptor rosarum…