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Soybean rust updates from states, national site
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Compiled by Marilyn Cummins, Editor
StopSoybeanRust.com
5/23/2005 -- Here's a roundup of soybean rust updates from various states and the national USDA soybean rust Web site:
National commentary on www.sbrusa.net:
The new news on the national commentary below the "Observation" map is the notation on Friday that the volunteer soybeans infested with soybean rust in Seminole County, Georgia, were being eliminated.
Ohio status on soybean rust:
Anne Dorrance of Ohio State University published this brief update today (5/23/2005):
"No further positive finds were posted last week on the USDA Web site. In addition, the first finding in Georgia, which occurred on volunteer soybeans, was destroyed. This reduces the inoculum load to only those locations in Florida. In conversations with some of my colleagues in the South, Louisiana is dry, and they have stopped planting for the time being. We will continue to monitor the situation as the season continues to develop. Most of Ohio’s 46 sentinel plots have emerged and are between the cotyledon and V1 (first true leaf growth) stage. One sentinel plot, Pickaway county, reported light feeding by bean leaf beetle. No other diseases or insect problems were reported."
Tennessee soybean rust update and sampling results
From Angela Thompson, Soybean Specialist, University of Tennessee:
PCR Testing Results – Week of May 20, 2005 -- All snapbean, kudzu and soybean samples submitted from West Tennessee were negative for soybean rust. No soybean rust has been observed in the southeastern United States outside of the confirmation(s) in southwest Georgia a few weeks ago.
Soybean sentinel plots in West Tennessee need rain just as our production acres do. Beans that started growing with the warmer weather are struggling again due to lack of moisture. Plots planted the first two weeks in April are mostly at V3 (two fully developed trifoliates), with one or two locations at V4 (three fully developed trifoliates). Plots planted the last week of April are at cotyledon to V2-V3 (one to two fully developed trifoliates), depending on the location. Central and east counties have received more rain this week than the western part of the state, which should help plant growth tremendously.
Texas soybean rust watch May 20, 2005:
Soybean rust was detected in the spring of 2005 on kudzu in central and southern Florida, and on volunteer soybeans in southern Georgia. The soybean field in Georgia will soon be destroyed; it appears that the rust is not spreading.
There has been nothing detected in the sentinel plots already established in Texas (Hidalgo, Victoria, Fort Bend, Jefferson, Ellis, and Delta, plus kudzu in Liberty). Dr. Charlie Rush, at the Texas A&M Agricultural Experiment Station in Amarillo, is currently planting sentinel plots in the High Plains.
The fate of these sentinel plots, as well as those in other states, can be found at the USDA Web site. This site has a map which will be useful in tracking the movement of soybean rust throughout the United States. The sentinel locations are marked in green. If rust is detected, the affected county will be noted on the map in red.
The plan is that if soybean rust is detected in states adjacent to Texas, there will be more extensive surveys of commercial fields. The weather in Texas is becoming hot and, shortly, it will be too hot for any introduced soybean rust spores to become established. At this time, I am not recommending any fungicide applications. -- Tom Isakeit, associate professor and extension plant pathologist, Texas A&M University, College Station.
Iowa State soybean rust weekly outlook:
Status of soybean rust. As of May 15, no new development of soybean rust has been observed since the detection of soybean rust in volunteer soybeans in Seminole County in southern Georgia.
Potential pathway from known source areas: See maps below of computer simulations for potential deposition areas of soybean rust spores from central Florida in late May and early June if a large amount of spores are produced there.
We used historical weather data to assess the potential spore deposition areas from central Florida where soybean rust has been detected. For modeling proposes, a large quantity of spores was assumed, although in reality, spore production so far is limited. Results show that even with the assumption of a large amount of spore production, the probability for spores to spread to other states, as indicated by the brown areas on the map, is significantly reduced compared with April and early May.
Keep in mind that the presence of spores does not necessarily mean occurrence of the disease. An example of this can be found in southern Brazil, where spores are present every year, but an epidemic occurred only one year in that region. For the possibility of spores moving out of Georgia, please refer to the May 9 issue of the ISU Integrated Crop Management newsletter.
Outlook: We should have passed the window for an epidemic that meets the worst-case scenario, although the risk of having outbreaks in the northern soybean production regions is still largely undetermined. In the worst-case scenario, the disease would establish itself in parts of the northern soybean production regions before July. Because the disease has not been found in other Gulf Coast states besides Florida and southern Georgia, the time to find the disease in Iowa should be no earlier than July with the current situation, or even later if the disease does not move in the next few weeks.
Authors: X.B. Yang, extension plant pathologist, and E.M. Del Ponte, postdoctoral research associate, Iowa State Department of Plant Pathology; and Zaitao Pan, St. Louis University.
Minnesota: Status of Asian Soybean Rust in the United States and Minnesota
5/20/2005 -- "Rust Watch" by Dr. Jim Kurle, University of Minnesota
The cold and wet start to the 2005 growing season is a powerful reminder of the role weather plays in crop production. Soybean rust, perhaps more than most crop diseases, is weather-dependent. We know from experience in other countries that in one growing season, weather conditions can help rust sweep across huge areas of a continent. We also know that in a season with slightly different conditions, rust can be limited to a much smaller area.
Scientists can use this knowledge to predict how various weather patterns might influence the spread of rust. For example, I recently had the opportunity to work with computer models simulating the spread of soybean rust in the United States during recent growing seasons. In 2004, the models showed that weather conditions would have allowed the disease to reach Minnesota in time to cause us problems. In contrast, the models indicated that 2003 weather conditions would have been unfavorable for the development of soybean rust.
It’s hard to know what to expect from the weather or from soybean rust. Fortunately, the National Plant Disease Forecast Center has rolled out its new Web site for soybean rust forecasts. On this site, farmers can get updated weather forecasts along with commentary on how conditions may make the outbreak of soybean rust more likely or less likely in a given area. Farmers can get the same information by calling toll-free at 1-888-835-2583.
As a complement to this site, farmers may want to visit the U.S. Department of
Agriculture’s soybean rust site at www.sbrusa.net. Here, farmers will find
recommendations specific to their state and maps showing where rust has been detected, where scouting for soybean rust is recommended, and management recommendations specific for their state.
This information is helpful enough right now, but it will be absolutely vital come July and August, when farmers’ ability to prevent major crop damage may depend on precise timing of their fungicide applications.
More from Minnesota:
As of May 13, 2005: Asian soybean rust continues to be of concern to soybean farmers in the United States and Minnesota, but the disease is at present restricted to the states of Florida and Georgia. Seminole County, (Southwestern) Georgia, is the latest county outside of Florida to report Asian soybean rust in 2005, according to the USDA Public Soybean Rust Web which reported it as of Wednesday, April 27th, 2005. This is also the first 2005 report of rust found on soybean plants -- the other three confirmations were found on kudzu (a weed in the southern United States) in three different counties in central Florida.
The risk to northern soybean production regions during this season still remains largely unpredictable. If the disease is found widespread in alternative hosts and volunteer soybeans in May in coast states including Louisiana, Mississippi and Alabama, computer models indicate that spores of the fungus can reach northern production regions before July. The next few weeks are critical. Keep watching the USDA Web sites for updates.
A number of efforts are being made to track soybean rust progress from one state, or region, to another:
Sentinel plots: Early disease-detection efforts will be conducted across Minnesota and Iowa during the 2005 growing season. Field locations at greater risk for disease will be monitored closely. The sites will be scouted weekly and a number of lower-canopy leaves will be removed and examined during each visit. Some sentinel plots will be located on public land, such as University experiment stations, while other ‘plots’ will be localized areas in much larger commercially-planted soybean fields. At this time there will be approximately 30 sentinel plots in Minnesota. In-field areas where plant leaves remain wet for extended periods (e.g., near tree rows, low spots or other protected areas) will also be scouted extensively.
North American Plant Disease Forecast Center: Researchers at North Carolina State University are currently tracking weather system movement from areas identified to have spores of Phakopsora pachyrhizi in the United States. The website provides information on weather systems and wind directions. It estimates the risks for high and low level air currents that might deposit rust spores in fields from infested locations up-wind. These efforts provide information on the risk for disease by identifying potential spore trajectories.
USDA soybean rust Web site: Plant pathologists and others from land-grant universities, regulatory agencies and private companies are submitting data from disease detection and monitoring activities to the USDA. The information will be used to track disease progress of soybean rust. Detection and monitoring efforts are already underway in several states, and are illustrated on the Web site’s maps.
A current list of approved fungicides and with spraying strategies for Minnesota are posted on the University of Minnesota soybean Web site, and on the Minnesota Department of Agriculture rust site.
University of Minnesota authors: David Nicolai, Regional Extension Educator-Crops, Hutchinson; Lisa Behnken, Regional Extension Educator-Crops, Rochester; Seth Naeve, Extension Specialist-Soybeans.
For an easy way to stay informed, sign up for the Monday Bulletin e-mail newsletter from www.StopSoybeanRust.com. You also will receive our RUST FLASH e-mails alerting you to important breaking news as soon as it occurs. All are archived in Bulletins.
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