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This issue begins one of several that will specifically address the soybean rust situation. In this issue, we'll focus on getting your sprayer set up and prepared. You may need to order new nozzles, since current "herbicide" nozzles will not likely do the job. And now is the time to place the order because most other soybean farmers are doing the same. I understand there is a backlog of orders.
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These recent finds are very disturbing in that they increase the likelihood that soybean rust will move into Virginia in 2005. Since kudzu is widely dispersed all along southeast, the weedy plant could serve as a bridge to moving rust up the east coast. Keep in mind however, that wind dispersal and the environmental conditions will ultimately determine when and where the pathogen will cause problems.
The worst-case scenario would be that rust moves north as kudzu greens up this spring. If this were to happen, we could find rust even before soybeans enter into the critical reproductive stages.
But, would this mean that we would be spraying soybeans before flowering? No, I don't think so. Rust seems to become recognizable on soybean leaves and begins to reproduce very rapidly after the crop begins to flower. There is little evidence that spraying for soybean rust during the vegetative stages is beneficial. We will not be making any fungicide recommendations before soybeans begin to flower.
However, if rust were to move into Virginia during the vegetative stages, chances of making multiple fungicide applications increase. This still depends on environmental conditions and infestation (inoculum) level. At this point, we feel that soybeans will have to be protected through the early seed development stage (R5). Once the crop reaches full seed stage (R6), yield losses from the disease will be much less. On average, there is about 6 weeks from the beginning flowering stage (R1) until the full seed stage (R6). Fungicides are generally effective for 2 to 3 weeks; so two fungicide applications may suffice in this worse case scenario.
On the other hand, it is not likely that rust will move rapidly until soybean is growing and provides the disease with more acres of suitable host. At this time, I'm sticking with my original assumption that we will not see the disease until August or even into September. Therefore, I still don't foresee us making multiple applications to the majority of our acreage in Virginia.
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The list of select agents and toxins was developed by USDA in conjunction with regulations governing the possession, use and transfer of these agents and toxins, which have the potential to pose a severe threat to public health and safety, to animal or plant health, or to animal or plant products.
This final rule revises the format and content of USDA's regulations, which prescribe registration, biocontainment/biosafety, incident response and security measures for facilities handling these agents and toxins to protect against the use of such agents or toxins in domestic or international terrorism.
Asian soybean rust is a fungal disease which was naturally introduced into the southeastern United States in the fall of 2004. Because the disease spreads primarily by wind-borne spores, it will continue to spread naturally. Asian soybean rust has been removed from the list of select agents and toxins to facilitate timely research on effective means to manage the disease.
These amended regulations are now substantially parallel to regulations promulgated by the Department of Health and Human Services' Centers for Disease Control and Prevention. The removal of soybean rust from the list of select agents was effective upon signature of the rule. The USDA and HHS final rules are scheduled to be published in the March 18 Federal Register. APHIS documents published in the Federal Register are available on the Internet at http://www.aphis.usda.gov/ppd/rad/webrepor.html.
Note by David Holshouser: This is very good news not only because it will facilitate timely research on control methods, but also because it gets the Dept of Homeland Security out of the picture. So, in Virginia, we will approach the first find more from an agronomic/control viewpoint instead of a homeland security viewpoint.
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Whether Virginian farmers will deal with soybean rust in the coming growing season is uncertain, but there are steps in preparing for disease control.
A diligent monitoring program, staying informed of rust movement and advisories, adequate spray equipment, and timely fungicide application(s) is vital in controlling rust in soybean fields this year. To help farmers best prepare for an intense spray schedule, specialists with Virginia Tech have collaborated to formulate a plan of action.
There are no soybean varieties currently available that have high levels of resistance to soybean rust. This leaves Virginian's with only one alternative option: spraying fungicides that are registered to control this disease. However, regardless of which fungicide is used, an effective job of controlling the disease is questionable if the fungicide is not applied properly with the most effective application strategy.
The single most important factor affecting prevention of this disease is complete coverage of the plant with fungicide. Fortunately, we have the technology; however, the producer may incur expenses with adaptation to the current application equipment.
Before listing a number of specific spraying recommendations for Soybean Rust, remember the 5 major principles that result in satisfactory and economic control of the problem: 1) Monitoring and early detection of the disease; 2) Selecting the right equipment, particularly the right type and size of nozzle; 3) Applying the correct fungicide (i.e., preventative versus curative) either before rust arrives or before 3% incidence; 4) Applying the fungicide in a timely manner to all acres; and 5) Checking the accuracy of equipment periodically to confirm correct application amounts based on label recommendations.
First and foremost, calibrate sprayers frequently to confirm the recommended amount of chemical is applied. Too little fungicide results in poor control and reduced yields, while too much wastes dollars and increases the risk of polluting the environment. How uniformly a fungicide is applied to the plant is just as important as applying the right fungicide and rate. Good control can be achieved by using the right equipment at the right time and at the right fungicide rate.
Extension engineers suggest farmers and commercial applicators preparing to control rust should consider three main aspects of operating their spray equipment:
Spraying fungicides is unfamiliar to some Virginia growers, and applying them is different than applying herbicides or insecticides. With a full soybean canopy, spray soybean rust with 20 gallons of water per acre. This is much more water than producers are accustomed to using in grain crops.
Good canopy penetration to reach the lower leaves and coverage are also essential. The key to good coverage with fungicides is having many smaller droplets vs. a few large droplets from the nozzle. "Medium" droplet size is preferred (250 microns ± 100 microns). Small droplets do not reach lower canopy, and larger droplets bounce off, or do not cover leaf surfaces. The actual distribution of different droplet sizes depends on pressure and volume, but this is a good target to shoot for. Higher pressures than those used for herbicide applications may be needed to achieve a medium droplet.
The boom height should assure good coverage over the canopy. Match boom height to nozzle spacing to provide good coverage and avoid skips in the top canopy. A combination that works well is a nozzle spacing of 20 inches and a boom height of 12 to 18 inches above the canopy for wide angle nozzles (110 degrees). Adjust boom height as necessary to improve coverage and penetration.
Timely spraying is also a key to reducing potential rust damage. Do maintenance checks on spray equipment so it will be ready when needed. Be sure equipment is large enough to spray all fields within only
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The single most important factor affecting the outcome of the fight against this disease is to get a thorough coverage of the plant with the fungicide. Research has shown that there is a very strong correlation between coverage and efficacy. We have the technology to achieve this, but it may come with higher equipment cost.
Nozzles producing cone pattern are not recommended for Soybean Rust. The flat-fan pattern nozzles are still the best choice as long as the droplets from these nozzles are categorized as fine to medium (200 to 300 micron). Check the nozzle catalog to find out at what pressure the nozzle you picked should be operated for it to produce fine to medium quality spray (note Table 1, p. 6). A flat-fan nozzle set up with two spray patterns seems to provide a better coverage of plants with fully developed canopies. Research has shown that hitting the target from two different angles, with one forward and one backward spray pattern, provides a more effective coverage than spraying with just one spray pattern shooting down. Several nozzle manufacturers have either the nozzles that provide a twin spray pattern from one tip, or special fittings/caps that allow the producers to place two nozzles in the same cap (Tables 2, p. 7), one pointed forward, and the other one pointed backward.
Soybean rust first shows its symptoms usually in the lower parts of the plant and works up towards the top of the plant. Detecting the disease early and using the most effective control mechanism are keys to controlling this disease. Complete coverage of the disease could be even more challenging if the symptoms of the disease are found at later stages of plant growth, when the plant is close to having a full canopy. Air-assisted spraying may help in facing those challenges. A commercial-scale sprayer with air assistance may add from $10,000 to $15,000 to the price tag of the equipment, but the added cost may well outweigh the income lost due to soybean rust in just one growing season.
Here are some specific recommendations to help achieve the best coverage and control when spraying for soybean rust.
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The spring months are the best time to thoroughly check the sprayer and calibrate it properly. Do this now before the arrival of Asian Soybean Rust. Successful fungicide control will largely depend on proper application. Proper application starts with selecting the right equipment, specifically nozzles, and spraying the right amount of fungicide uniformly across the field.
Pesticide manufacturers have invested heavily to determine the most effective and economical application rate for the fungicides labeled for Soybean Rust. However, the applicator must assure the recommended amount is applied.
Why calibrate? Calibration is the best way to assure you are delivering the desired rate. The window of opportunity to spray for soybean rust is much narrower than for most pests. You may not have the time to calibrate after the rust has arrived.
Results of many "Sprayer Calibration Clinics" show that only a third of applicators are applying chemicals at a rate within 5 percent (plus or minus) of the intended rate. Calibration takes about 30 to 60 minutes and requires only three "tools": a stopwatch, a measuring tape, and a jar graduated in ounces. Several calibration methods are available but the one described below is simple, straightforward, and does not require cumbersome equations.
"Ounce" Calibration Method. When the spray tank is clean, fill it at least half full with water since the amount of water in the tank may affect travel speed. Measure the distance between nozzles in inches and then drive a designated distance depending on the nozzle spacing. For a nozzle spacing of 20 inches, drive 204 feet at normal spraying speed. Drive 136 feet for 30-inch spacing; 113 feet for 36-inch spacing; and 102 feet for 40-inch spacing. Run the parked sprayer at the same pressure level for the same amount of time it took you to drive the designated distance, and collect the output of each nozzle. Calculate the average nozzle output by dividing the total output from all nozzles by the number of nozzles tested. The average nozzle output in ounces equals the gallons per acre applied. For example, if you catch 20 ounces the rate is 20 gallons per acre (gpa).
The next step is to minimize the application error. If the difference between your intended application rate and the actual rate is greater than ± 5 percent of your intended rate you should make some adjustments. For example, if your intended application rate is 20 gpa, the calibrated rate should be between 19 and 21. For small changes in the application rate try adjusting the pressure. For larger changes either adjust the travel speed or replace nozzles with the appropriate size. You need to repeat the calibration process until your application error is no greater than ± 5 percent.
The "Ounce" calibration method is explained in detail in Virginia Extension (VCE) Fact Sheet 442-453, available from your local Extension Office, or from the VCE web site: http://www.ext.vt.edu/pubs/bse/442-453/442-453.html.
Just spraying the right amount of fungicide on each acre is not enough to achieve effective control of soybean rust. Uniform deposition on the spray target is as important as the total amount deposited. Each nozzle type produces a unique spray pattern. Some nozzles require precise overlapping of patterns from adjacent nozzles. Check the nozzle catalog to find out the appropriate boom height for your nozzle spacing that will produce uniform spraying across the boom.
Calibrate frequently. Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used may require a new calibration. A survey showed that the more often a sprayer was calibrated, the more accurate the application rate. Be prepared to spray for soybean rust before it arrives and have your sprayer calibrated.
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Aerial applications have proven successful in controlling soybean rust in Brazil. Because they can cover large acreages very quickly, and are not limited by wet soil conditions, aircraft have significant advantages in timeliness over ground sprayers. By changing deflector angle or orientation of an aerial nozzle, the droplet size spectrum can be altered to best match fungicide application requirements.
The Aerial Spray Nozzle Models (http://apmru.usda.gov/downloads/downloads.htm) developed by the USDA Agricultural Research is a valuable tool that aerial applicators can use in setting up their aircraft. By entering the nozzle type, orifice size, nozzle or deflector angle, pressure, and air speed, the model calculates the droplet spectrum and other valuable information. This allows an aerial applicator to set up the aircraft to create the droplet spectrum required for a job. Good control of droplet size is one of the reasons agricultural aircraft can successfully make soybean rust applications at five gallons per acre.
Agricultural aircraft have the advantage of speed and the ability to spray when field conditions are too wet for a ground sprayer. Thus, aircraft have significant advantages in timeliness over ground sprayers.
While keeping the boom as low as possible works well for ground applicators, flying too low can actually increase drift and reduce deposition for aerial applicators. An ideal height for aircraft to fly is often between 10 and 14 feet above the canopy. Any higher and the droplets are excessively exposed to wind. At lower heights, droplets can become trapped and carried off in air turbulence caused by the aircraft flying so close to the crop canopy. Whether using aerial or ground applications, it is important to follow the proper guidelines as closely as possible.
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A. Nozzles with a flat-fan pattern, compared to cone pattern, seem to be better choices for soybean rust. However, we are not recommending use of air-induction nozzles to treat rust, even though they provide flat-fan patterns. These nozzles produce relatively courser droplets, which do not provide the desired coverage for fungicides in soybeans.
Set up your sprayer so that the nozzle spacing is 20 inches, and then adjust the boom height (above the target) so that proper overlap is achieved on top of the canopy. Check the nozzle catalog for the proper boom height depending on the spray pattern angle of the nozzle.
A small size (size 02 or 03) Turbo TeeJet Duo at 60-70 psi is a better choice than the same size TwinJet. Do not use size 02 and 03 TwinJet nozzles operated at higher pressures, because they create too many small droplets that do not penetrate into the canopy. If you use TwinJet nozzles, the minimum size you should select is size 04 (TJ 8004).
Overall recommendations:
Dr. Bobby Grisso, Extension Ag Engineer
A: Virginia began preparing for soybean rust over a year ago. I visited Brazil last March to see the disease firsthand and better understand how to manage it. Dr. Erik Stromberg has been very active cooperating with other states and regional projectsto develop management strategies and publications.
We formed a Virginia Soybean Rust Task Force last summer. It consists of over 15 people from industry, VDACS, farm and commodity organizations, and Cooperative Extension. As part of this task force, we developed an response and action plan last summer. We recently met on March 23 to review our goals and update our plan of attack. When soybean rust was found last November, the action plan was implemented.
We trained over 75 "first detectors" last September. Attendees were primarily Extension Agents and crop advisors, but also included farmers and other interested personnel. The goal to these all-day classroom and field sessions is to enable a cost-effective, widespread network of trained observers to monitor Virginia soybean fields and report their findings back to a central location.
Last summer, we also conducted a soybean aphid and rust monitoring program at the request of the Virginia Soybean Board. We scouted 78 fields in 33 counties on a bi-weekly basis to detect aphids or rust. Although we did not find any rust, we did find aphids earlier than we've ever detected them in Virginia (early July). We will expand this program in 2005 to include about 100 fields and an increased area of coverage. Due to our experience last year, we feel very comfortable in conducting this survey and will use this as one of our main weapons in fighting the disease. I must commend your Virginia Soybean Board for effectively utilizing your check-off dollars.
Missing from last year's survey was a good communication system for getting out information, advisories, and recommendations. We have plans to implement a tracking, monitoring, and advisory service in 2005. Such a service should allow 24/7 access to our control recommendations and other information regarding soybean rust. A Virginia-specific web site is now being constructed and we also plan to include a call-in phone service.
Finally, we will continue our educational efforts with presentations and field days. We presented rust information at over 20 county grower meetings this winter and those meetings are continuing into the spring. We plan on demonstrating sprayer technology at this year's Ag Expo field day and will continue to test fungicides and conduct other research as part of the On-farm Testing Program led by our County Agents.
In summary, we are prepared.
Dr. David Holshouser, Extension Soybean Specialist
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Table 2. Twin nozzles configurations and the corresponding pressure and travel speed ranges to achieve "Medium" droplets at a 20" nozzle spacing and 20 GPA.
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Sincerely,
David L. Holshouser
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