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Alert: July 25, 2006 |
Expect Charcoal Rot Soon on Soybeans, Corn and Grain Sorghum |
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Expect Charcoal Rot Soon on Soybeans, Corn and Grain Sorghum On a recent trip to central Kansas, many fields were under high drought stress. Some fields of corn and grain sorghum were beyond reasonable recovery even if rain comes and a number of soybean fields were hanging on by a thread. They were already suffering some flower and pod drop and some of the leaves were beginning to scorch. Hot, droughty weather with soil temperatures in the 90N+ F range are ideal for the development of charcoal rot. While it is difficult to separate the effects of charcoal rot from simple drought stress, a good rule of thumb is that plants infected with charcoal rot will die about two weeks earlier from dry weather than plants that do not have charcoal rot. Grain fill that would have occurred during this period is the amount of yield loss that can be attributed to charcoal rot. Corn and sorghum will die prematurely. When stalks are split, the typical shredded appearance in the lower stalk associated with all stalk rots will be present. Additionally, there will be a gray to black discoloration of the inner stalk caused by numerous sclerotia (small, black reproductive structures of the fungus) forming on the vascular bundles and decaying tissue. On soybeans, the plants will slowly wilt and die over a one- to two-week period. The leaves will remain attached. If the tap root is split, there may be a brown or black discoloration of the inner root. Just under the surface of the outer root tissue, sclerotia can sometimes be found, although these may not form until the plant is completely dead. Other symptoms may include a browning of the inner stem starting at the soil line and moving upward. After plants have died, sclerotia may form on the outer stem and branches giving the dead plant a silvery-gray appearance. Earlier maturing varieties and hybrids of all crops are the most susceptible. Other than irrigation or rain, there is little that can be done now. Choosing corn and sorghum hybrids with good stay green characteristics is helpful. Reducing seeding rates of soybeans to fewer than 125,000 plants per acre is also helpful. (Jardine)
Hot, Humid Weather Triggers Two Turf Diseases Last week’s extremely hot, muggy weather led to outbreaks of brown patch and Pythium foliar blight, two diseases of turfgrass. We (and the turf) had a brief respite during the cooler weekend, but now it is heating up again. Both diseases are favored by hot weather, especially warm (above 68F), humid conditions at night. Both diseases affect the cool-season grasses: (bluegrass, ryegrass, fescue, and bentgrass). On warm, dewy mornings, both of these diseases can develop fluffy, white growth among the blades of grass (see photo of Pythium growth on turf plug). Brown patch is definitely the more common disease in Kansas, especially in home lawns, but it is important to keep Pythium in mind. Brown patch is caused by a true fungus, and Pythium blight is caused by an oomycete (water mold) so some chemicals for brown patch do not work for Pythium, and vice versa. Especially in a commercial turf/golf course situation it is important to know which disease you have in order to choose proper controls. In the diagnostic lab we have been receiving samples of both of these diseases, and (like with most diseases) we need a microscope to distinguish them because they can appear quite similar. Brown patch has been appearing in all kinds of turf from home fescue lawns to golf course greens. For more information on brown patch you can look back at the Disease Alert from a couple of weeks ago at http://www.plantpath.ksu.edu/DesktopDefault.aspx?tabid=527. In most cases, especially a home lawn situation, the turf will recover from brown patch once the weather pattern changes. |
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Pythium foliar blight is a more damaging disease, and more of a concern on golf courses. It showed up last week at several courses in the eastern half of Kansas. Pythium is a serious disease and can take out large areas of turf practically overnight. Pythium can spread in water, such as drainage patterns, and on clippings, mowers, shoes, etc. During a Pythium outbreak it is important to avoid mowing and other traffic when active growth is present. There are several fungicides available for commercial Pythium control such as azoxystrobin, chloroneb, fosetyl-Al, mancozeb, metalaxyl & mefenoxam, phophite products, propamocarb, and pyraclostrobin. Even with the best chemicals short spray intervals are recommended. (Kennelly) |
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Disease Highlights Heat & Drought stress
in crops, landscape and garden
Contributing Author(s): Megan Kennelly
kennelly@ksu.edu
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Web updated 9/01/06 |
