By Jane Milliman
Fungi are some of the most common garden invaders, lying in wait to attack grass, flowers, shrubs, trees, and vegetables. They live in the soil or decaying organic matter, are usually more prevalent in wet weather, and benefit from good air circulation. They can be spread by bugs, splashing water, or through the air. Fungi come in many forms—here are some you might see in your landscape.
Snow mold. This earliest fungus can be either gray or pink and starts growing in winter. It usually goes away on its own, but you can apply a fungicide if necessary. To prevent it, dethatch grass regularly and don’t let it go into winter unmowed—3 inches is an ideal height. You might also hold off on fall fertilizing. (Photo credit: flickr:noricum)
Blight. Here’s a little-known fact: The very same fungus that caused the Irish potato famine also is the tomato’s number one enemy. We call it “late blight,” which is a pretty boring name for something that causes so much havoc. Late blight spores spread through splashing water, so be very careful when irrigating. To ensure as sterile an environment as possible, start your own tomatoes from seed, buy seedlings from a reputable source, rotate crops, and choose resistant varieties. If your area is prone to late blight, consider a prophylactic fungicide treatment. There is an “early blight,” too, which is somewhat less problematic.
Powdery mildew. Spread by aphids, this fungus can attack almost anything but particularly enjoys lilac, phlox, lungwort and squash. For the most part it’s just ugly, but it can weaken a plant, making it more susceptible to other, more dangerous pathogens. Try a 4:6 mix of milk and water, or opt for a commercial spray.
Black spot. Rose lovers know this one. People have been known to give up tea roses entirely due to this pesky fungus (as well as mildew and rust, also fungi), but that’s not necessary.
Breeding advances are such that you can buy many resistant varieties. It might be worth tearing out the old and planting some new roses. But if you have roses you can’t live without, fungicide is your friend.
Tar spot. Like anything else, plants can become trendy. When landscapers and municipalities find something that works, they use it a lot. The problem is, without diversity, a monoculture forms. Think about Dutch elm disease, a fungus that denuded entire neighborhoods throughout the Northeast beginning in the 1940s.
Now we have entire neighborhoods planted with Norway maples, which are particularly susceptible to tar spot. Luckily, tar spot doesn’t kill the trees, but it sure makes them look funny. There isn’t much point trying to treat it, but you can rake up the leaves in fall and dispose of them offsite. (Photo credit: Brian Eshenaur, Cornell Cooperative Extension)
There are many, many more fungal invaders out there, some treatable, some not worth bothering with. Remember that the best defense is a good offense. Water your garden enough to prevent drought stress. Remove diseased foliage from plants (when they are dry, not after a rain) and dispose of it. Also, be sure to sterilize pruners with a 10-percent bleach solution between cuts.
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