KENNEWICK -- Woe is me! The cool weather has slowed down our gardening season so much that I've almost abandoned hope that I'll get ripe tomatoes before the end of summer.
Slow growth isn't the only problem that the abnormally cool, moist weather has been causing. These conditions have been perfect for fungal plant diseases on certain garden and landscape plants.
When it comes to fungal plant diseases, local gardeners usually can consider themselves lucky. Our typically dry climate isn't conducive to an abundance of troublesome fungal diseases, but this spring's cool temperatures and repeated rains have created the perfect conditions for trouble.
Sycamore anthracnose is a fungal disease which attacks sycamores. Look around at many of the older area sycamores. They look like they are slow to leaf out this spring, but the problem is anthracnose that attacked the leaves as they first began to emerge. Severe infections of sycamore anthracnose occur if the weather is cool (below 55 degrees) and moist when the leaves start to emerge. Years when our spring weather is warmer (above 60 degrees) or drier, anthracnose is not a problem.
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By the time anthracnose is noticed, it's too late to apply fungicide sprays that will protect the emerging leaves. Fungicides must be applied just as the buds begin to swell and open. Repeat applications are needed if the weather stays cool and wet. Many sycamores look pretty sick right now, but most will survive by producing a second set of leaves. Hopefully, this new set of leaves won't also become infected, but they can be protected with fungicides sprays.
While anthracnose seldom kills sycamores, it can render them pretty ugly after repeated attacks. Fertilizing affected trees to encourage new growth is recommended. If you are considering planting a sycamore, select one of the anthracnose resistant cultivars, Bloodgood or Liberty.
Powdery mildew is a group of diseases identified by whitish powdery spots or patches on the surface of green leaves and stems. Young, succulent tissues of susceptible plants are most prone to infection. Badly infected growth usually becomes stunted and distorted.
The different powdery mildews look very similar, but only attack specific host plants. Rose powdery mildew is different from the powdery mildew that attacks grapes, and the one that attacks lilacs, and the one that attacks apples, and the one that attacks turf.
Unlike many other fungal plant diseases, powdery mildews don't need free water on leaf surfaces for infection to occur. Instead, they are favored by cool temperatures, high humidity and lower light intensity. Our weather this spring has been very conducive to powdery mildew infections. Powdery mildew also can be a problem when gardeners create favorable conditions by crowding plants, which causes poor air circulation, situating plants in damp shady areas or irrigating lightly but frequently.
Problems with powdery mildew can be mitigated by planting mildew resistant varieties, avoiding crowded plant growth, properly pruning to remove excess growth and planting in full sun. There are dormant fungicides available for control of powdery mildew on woody plants that should be applied just before growth begins in the spring. New growth can be protected with regular applications of fungicide. So far, I've been seeing powdery mildew on crab apples, ornamental pears, apples and roses.
It's a good idea to check your garden for signs of insect pests and plant diseases, such as powdery mildew.
This year our plants need all the tender loving care that we can provide.
How does your garden grow?
* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension.