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Alert: September 1, 2006 |
Recent Rains Have Activated Water-Loving Landscape Pathogens |
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Recent Rains Have Activated Water-loving Landscape Pathogens Last week I sent this article out in the Horticulture Newsletter. The rains have continued, and these organisms are still popping up so I thought I should send this information out this week in the Disease Alert for those who do not receive HortNews or who missed it last week. The wet weather has activated various organisms such as the root-rot pathogens Phytophthora and Pythium. These pathogens are oomycetes (water-molds), and there are multiple species of both types of pathogens. While known primarily as root-rot pathogens they can also cause symptoms in above-ground tissues. These organisms are present at some level in most soils, and they can have explosive growth in wet conditions. |
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A few days ago we got a report of vincas succumbing to a Phytophthora parasitica epidemic triggered by the rain. The symptoms developed on aerial plant parts (see photo). This Phytophthora has a wide host range including bean, eggplant, melons, onions, petunias, snapdragons… many kinds of plants. Certain vincas are particularly susceptible, however. The key to managing these diseases is prevention. Try to improve drainage, such as building raised beds. If you have a problematic site, or a history of these diseases, consider using landscape plants that are less susceptible. Chemical controls are inconsistent, especially once the disease is already established. For home lawns there is a chemical called pentachloronitrobenzene (PCNB) that has been available in the past, but its use is being phased out by the U.S. Environmental Protection Agency. Commercial operations have some other options, but the cultural tactics must be used too. (Kennelly)
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Rains Bring Bumper Crop of Mushrooms Too Other organisms that have popped out in the recent rainy weather are mushrooms and slime molds in lawns. Most of these organisms are harmless to plants, though certain mushrooms are associated with a condition called Fairy Ring which can sometimes lead to brown rings in turf. I mentioned fairy rings in an earlier newsletter (http://www.plantpath.ksu.edu/DesktopDefault.aspx?tabid=537) and included a photo of dark green rings. This week, after the rains, the mushrooms associated with some of these rings have appeared (see photos). The mushroom-producing fungi spend most of the time growing through the soil as a network of microscopic threads, consuming organic materials. Moist conditions induce them to produce the mushrooms, their spore-producing structures.
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Slime molds are not fungi. They are primitive microorganisms that come in many shapes, colors, and sizes. There’s even one affectionately known in some circles as the dog-vomit slime mold (http://botit.botany.wisc.edu/toms_fungi/june99.html). Slime molds commonly occur in lawns and mulch, and they consume other microbes such as bacteria (they don’t consume plants). Slime molds produce spore masses that break open and spread in rain or when mechanically disturbed by a rake or a stray soccer ball shooting across the yard. The two photos of slime molds included in this newsletter were sent in electronically through our PDIS system from Cheyenne County, thanks to Tye Faulkender. While these photos were sent earlier this summer, slime molds are making appearances now after the rains.
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Disease Highlights
Alfalfa: Spring black stem, summer black
stem, alfalfa mosaic
Contributing Authors: Megan Kennelly
kennelly@ksu.edu
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Web updated 9/01/06 |
