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So, with that in mind, here's the second issue of the Virginia Soybean Update devoted solely to soybean rust. I'll continue to focus on the issue this year (and probably in the coming years). But, you'll also be getting newsletters dealing with other non-Rust topics. Expect the May issue in a few days. We'll return to so non-rust items in that issue.
But, even if you are tired of hearing about rust, don't tune out. There's too much at risk. But knowledge of the disease and its movement will greatly reduce the risk. Keep informed and don't stop listening.
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What does this mean for Virginia? It's still too hard to tell. As I stated in the last newsletter, the worst case scenario, would be that the rust begin to move up the southeastern coast on kudzu. Most soybeans in the southeast are not planted until May, but kudzu and other alternative hosts are now emerging. I once heard that if you picked up a kudzu vine in Georgia, you could shake the entire state. While this may not be entirely accurate, the state does have over 150,000 acres of the stuff. This could serve as an early season bridge to the disease and allow it to move up the coast much quicker than it would if it were only moving on soybean.
But, just because rust continues to be detected in other counties doesn't mean that it will move rapidly up the coast. You must remember that the amount of inoculum is important to the disease's movement.
More details on the last Florida finding were announced last week. The rust was on one small section of vine that had emerged from the soil just on the edge of a dirt road. The intensity on that section was moderate to high. The researcher found no other suspect samples at that site. He subsequently surveyed that site again (with negative results) and will continue to do so on a weekly basis. Based on those observations, the researcher concluded that the intensity level for the entire site to be very low. On the other hand, the rust was found on several volunteer soybean plants across the field in Georgia.
So, rust moving up on kudzu and volunteer soybeans is a worse case scenario. But, more rust than present on the Florida discovery will be required to cause such a movement. Realistically, I don't think the disease will not likely move rapidly until we see large acreage of soybean growing.
So, when will it arrive in Virginia? We don't know. I still think that it'll be late summer. The disease doesn't do all that well on seedling soybean. Only after flowering does soybean rust seem to show itself. If we stick with our traditional maturity groups, or more importantly, if the states to our south stick with their traditional maturity groups, then an inoculum buildup shouldn't start until July or later, when our traditional maturity groups enter into the reproductive stages. If this were the scenario, then we'd probably begin seeing the disease in August. Most of our full-season soybeans will be well on their way to producing pods and seeds by this time. So, a maximum of one timely fungicide application would be sufficient. Double-crop soybeans will be a different story though due to later maturity date.
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So how will keep you informed and make fungicide recommendations? First, Virginia is part of the coordinated framework for soybean rust surveillance, reporting, prediction, management, and outreach. This USDA-facilitated framework will provide soybean producers and other stakeholders with an effective decision support for managing soybean rust throughout the season. The basic objectives of this framework are:
The best thing about the coordinated framework is that it keeps the communication lines open throughout the U.S. In addition, we have access to the best minds regarding this problem. If interested, the framework is posted at http://www.aphis.usda.gov/ppq/ep/soybean_rust/coordfram041405.pdf. This is a 
PDF file and is quite large (42 pages); so it will take a while to download.
Probably the most valuable part of the network to you directly is the USDA Soybean Rust Information site at http://www.sbrusa.net/. (shown below). On this site, you'll find where soybeans (or other hosts) are being scouted, whether or not rust has been found at those locations, disease management recommendations, and scouting recommendations. Since the map is geo-referenced, you can zoom into any county and find details of scouting sites and county-specific recommendations. You can overlay cities, interstate highways, and soybean production areas on the map. You'll see commentary coming from either me or Drs. Stromberg or Phipps, when you zoom into Virginia. In general, site should provide all you need to know about controlling rust this year. So check out the site and learn to navigate around.
The ability to make county-specific recommendations is a valuable component of this site. For instance, let's say you chose the Disease Management thumbnail and zoom into Virginia, you might see something like the map below. Yellow colored counties indicate that no fungicide is yet required; blue that a preventative fungicide can be used; and red that a "curative" fungicide or tank-mix is needed. THE MAP BELOW IS ONLY AN EXAMPLE AND NOT CURRENT RECOMMNDATIONS. While this will not likely be representative of what our recommendations will look like, it gives you an idea of what to expect.
Finally, when we feel that rust spores have moved into Virginia, we will update the scouting map to indicate where intense scouting needs to begin. So, you might see a map such as the one below. Again, this is not our current scouting recommendation.
The web site should provide a valuable means of staying up-to-date on the rust situation. But, the public site is only part of this web-based system. State specialists and designated observers will have access to a restricted (not for public access) part of this system. Here, we'll be able to see all monitoring locations, including sentinel plots, where soybean rust is suspected but not yet confirmed, detailed information from individual monitoring sites, and disease severity models that predict disease progress. This information will help us to make management recommendations.
In addition to the USDA web site, I want to call your attention to another site, the North American Plant Disease Forecast Center. This site has provided valuable information via the internet to tobacco and cucurbit growers for years and is now providing similar information on soybean rust. The soybean rust forecast home page can be found at http://www.ces.ncsu.edu/depts/pp/soybeanrust/. The site provides "timely information on the occurrence of soybean rust and future movement of inoculum (fungus spores) across the North American continent."
As you scroll down the page, you find an outlook section stating whether there is a low, moderate, or serious threat and risk for soybean rust spores to move to new areas. Keep in mind that this is only a weather model and not an actual tracking system of rust spores.
Another important site that I want to call your attention to is our own Virginia Soybean Rust website, http://www.ppws.vt.edu/ipm/soybeanrust/index.htm. Although still under development, we hope to provide Virginia growers with site that most, if not all information pertaining to soybean rust and how it is affecting Virginia can be found. On the home page, you find current Virginia recommendations, the threat of spread from sources of soybean rust, risk in Virginia, and scouting and fungicide recommendations. We'll also provide a direct link to the two sites discussed in this article. From this page, you'll be able to access other sites as well. So, mark this page as a favorite on your web browser.
Finally, we are investigating a call-in service where you can get the latest soybean rust forecast and recommendations. Since most producers are using a cell phone and 800 numbers don't help in that regard, we'll probably just record a message on a phone at one or several of the AREC's.
In summary, there should be no reason why Virginia's are kept abreast of soybean rust in 2005. Our goal is to minimize yield loss and reduce unnecessary fungicide application, both of which will add to the bottom line.
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The point is to aid in our fight against soybean rust. How will this help? It should greatly assist in our monitoring efforts. You see, for some reason, soybean rust does not really do very well on seedling soybeans. Only after the plants flower will the disease begin to rapidly produce pustules and spores. So, even though rust spores may have landed on a soybean field, we might not be able to detect it, if the crop is still in the vegetative stage.
Enter an early-planted MG 3 variety - by planting small fields or areas within a field with a MG 3 variety, we can detect rust two to four weeks before it is detectable in the rest of the crop. These "sentinel" plots give us a "heads up" on where rust has invaded. And if soybean rust has invaded, a "curative" fungicide will be needed when the rest of the crop enters the reproductive stages; "preventatives" will no longer be effective by themselves.
A sentinel can be defined as a sentry or something that watches over or guards a point of entry or passage. So, in a sense, we're using these plots to watch over the rest of the crop. I actually prefer the term "indicator plot" since the plot itself is not actually protecting the rest of the crop. But I suppose "sentinel" sounds better and has evidently stuck; so we'll use it.
The most important function of a sentinel plot is to serve as an early warning system for new rust infections throughout the U.S. soybean production region. The U.S. has set up a sentinel plot network in all soybean growing areas. This network will let us know when and where rust is moving in the U.S., much earlier than if we just relied on traditional maturity groups planted at traditional planting dates. Below is a map showing all sentinel plot locations currently established (as of April 28) in the U.S. The map is not completely up-to-date. I know that North Carolina has about 20 plots planted and I'm sure other states do as well. We have only planted four such plots in Virginia, but that number should grow to about 30 within the next two weeks. But, as you can see, we should be able to track rust effectively.
Another function of a sentinel plot is to learn more about the disease and how it spreads in the U.S. This includes quantifying the timing of spore production in overwintering and growing season sources of inoculum. Some sentinel plots will be used as a means to collect data to better understand the factors involved in the causes and distribution of soybean rust (epidemiological research). Five epidemiological research plots will be located at the Northern Piedmont (Orange), Southern Piedmont (Blackstone), Eastern Virginia (Warsaw), Tidewater (Suffolk), and the Eastern Shore (Painter) AREC's. They will not be sprayed to allow better study of disease development. More detailed data will be collected from these plots versus the others.
So, sentinel plots will basically serve as an early warning system and as a means to understand the disease better. As I mentioned earlier, we're located about 30 of these plots on farmer's fields throughout Virginia, just as we did last year. Keep in mind that the plots not being used for research have extra value only during the early part of the growing season (June and early July). Once our MG 4's enter into the reproductive stages (usually late July and August), those varieties, in a sense, become sentinel plots for later MG's.
I want to make it perfectly clear that if we discover rust in a sentinel plot, growers should not immediately spray the rest of the farm. I do suggest spraying the sentinel plot to keep the disease inoculum load down and to prevent yield loss. But spraying fungicide before the reproductive stages has shown no benefit. Only after flowering should fungicides be used.
As mentioned earlier, the presence of soybean rust in sentinel plots will warn us that a "preventative" fungicide will have less value once sprays are begun on the rest of the farm. Preventative fungicides can still be used, but only in combination with a "curative" product.
That's how we and others in the U.S. will be using sentinel plots. I do believe that they have much value. In Virginia, we will use those plots at a hub for other fields to be scouted in an area or county.
I want to thank several seed companies for providing soybean seed for our sentinel plots. I think this shows commitment to our growers from our seed company partners. The following companies donated seed: UAP/Dynagro Seeds (50 bags!); Pioneer; Delta & Pine Land Co.; Vigoro Seeds
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For those of you that aren't familiar with tramlines, I'll try to briefly describe them. Tramlines are basically traffic lanes placed in a field at planting. These traffic lanes match the width of the sprayer tires and are spaced to match the width of the spray boom. See the diagram below for clarification.
Tramlines have several advantages. One is uniform application of nutrients and pesticides, with no skips or overlaps. With soybean rust, you'll easily be able to tell where the skips are. And doubling of fungicide on some parts of the field will definitely not compensate for the skips in the other parts. Another advantage is that they act as a guide for repeated applications. Tramlines are much easier to follow than foam markers. And, tramlines offer a means to control traffic and reduce compaction. Of course today's technology (i.e., light bars, auto-steer tractors, etc.) will accomplish the same results. But, there are more advantages.
Tramlines may actually help with spraying in wet fields because the unplanted strips become somewhat compacted. There is less likelihood that the sprayer will be stuck in the field. Remember, soybean rust will not wait for the fields to dry.
But, probably the most important advantage of installing tramlines in soybeans is higher yields from not running over 2-3 feet tall soybeans. Of course if you're in wide rows (>20-24"), you won't need tramlines. But, most of Virginia's acreage is planted in 7 1/2 to 20 inch rows, making it much harder to fit a sprayer without damaging the crop. We've seen a rapid move to drills, and we experienced the yield increases associated with that move, especially for our double-crop plantings. But, these yield increases could be negated if we run over one or two rows while spraying for rust.
There really hasn't been very much research conducted concerning the effect of running over soybeans late in the growing season. But, there is some data out of Ohio and it is shown below. The research was conducted on 7 1/2 -inch soybeans and two of the rows were destroyed during pesticide application. Note that the amount of yield loss varies with the spray boom width because less total rows are damaged. But, even with a large boomed sprayer, yield losses approach 1/2 to 1 bushel per acre. You need to just add this cost to your fungicide application cost, if not using tramlines.
| Spray Boom Width (ft) | No. of Rows Covered/Pass | Percent Yield Loss |
| 50 | 80 | 2.5 |
| 60 | 96 | 2.1 |
| 70 | 112 | 1.8 |
| 80 | 128 | 1.6 |
| 90 | 144 | 1.4 |
Do we lose any yield due to tramlines? In full-season soybeans, I'd say no. In double-crop, I would suspect that we'd lose a little. But, I'd also suspect that the yield loss without trams would be higher. I'll be conducting some research to evaluate that this coming year.
In summary, I feel that the time is right for tramlines in soybeans. Installation is fairly simple. For the simplest system, you can just block the drill openings that correspond to the tramlines. Or, you can purchase devices that establish the lanes only where you want them.
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Sincerely,
David L. Holshouser
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