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Fight plant disease
6 Aug, 2009 By: Brian Albright Get Growing Powdery mildew on Lamium. |
Nothing mars the appearance of an otherwise attractive landscape like yellow, brown or wilted plants. Fungal and bacterial diseases can lay waste to ornamentals and perennial gardens if left uncontrolled, leaving plants deformed, stunted, defoliated or worse.
With proper planning and plant care, though, many common diseases can be effectively treated or avoided altogether.
This year, the eastern half of the U.S. has experienced unseasonably cool and wet summer weather, leading to an increase in fungal infections in many landscapes and gardens.
"We are seeing more bacterial problems than we normally do, as well as foliar leaf spots and blights on perennials," says Sharon Douglas, head of the Department of Plant Pathology and Ecology at the Connecticut Agricultural Experiment Station.
"The weather has exaggerated the diseases appearing this year," adds Margery Daughtrey, senior extension associate at Cornell's Department of Plant Pathology. "These diseases are always around, but are much more obvious when you have this kind of rainy weather."
That's why it is important to be able to identify and treat the most common problems, and care for plants in a way that's unlikely to contribute to future infections.
Common disease types
The most common problems in the landscape are typically foliar leaf spots or blights. Leaf spot can be caused by both fungi and bacteria, and result in dark blotches or spots on foliage of perennials like irises, phloxes or hellebores.
Gray mold (botrytis) frequently appears on flowers, and is common on roses and geraniums. "Gray mold is very tough to control, especially when we have weather like this," says Steve Nameth professor and associate chair of the Department of Plant Pathology at The Ohio State University.
Mildews thrive in the type of cool, wet conditions that have been present most of this spring and summer. Powdery mildew can be found on a wide variety of plants, including phlox, lungworts and peony, and causes plants to develop white and gray blotches on leaves. Downey mildew, on the other hand, appears as a fuzzy white or gray growth on the undersurface of leaves, buds, flowers and stems. It's often more difficult to spot and to control, and can affect black-eyed susan, speedwell, bluets, dead nettle, roses, and other plants.
Leaf and stem rust, as the name implies, causes rust-colored spots on leaves, and can be seen on hollyhocks, asters, pansy, phlox and hibiscus, and daylily.
More serious diseases, such as root, stem and crown rots, will make plants to turn yellow and droop, and often stunt growth. Vascular wilts, caused by fungi and bacteria, block water within the vessels of the plant, causing serious growth impairment or death.
Ornamental shrubs and trees can also be afflicted by mildews, leaf spot and wilt, along with Anthracnose (which causes spotting on leaves and defoliation), heart rot (which decays trunks and limbs), cankers, leaf curl viruses on ornamental trees, and monilinia fungus (brown rot) on fruit trees.
For the full article, see the Livescapes section of the September issue of Landscape Management magazine.
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