Ask Dr. Jim

Questions & Answers

Dr. James Barrentine, formerly head of the Department of Crop, Soil, and Environmental Sciences at the University of Arkansas, is Director of Technical Services for Cheminova, Inc. He has been a key player in the development of numerous crop protection products and is recognized throughout the industry as a consummate professional. Dr. Barrentine is a past president of both the Southern Weed Science Society and the Weed Science Society of America, and in 1998, was given that organization's Outstanding Industry Member award. He has both a B.S. and M.S. degree in agronomy from the University of Arkansas and holds a Ph.D. in weed science from Purdue University.

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1. What is TOPGUARD™?
   
   TOPGUARD™ is an Asian Soybean Rust fungicide that has been exempted from registration for emergency purposes to address soybean rust in selected states. TOPGUARD™ is sold in the United States by Cheminova, Inc. This product has provided very effective control of soybean rust in other parts of the world, such as Brazil. TOPGUARD™ has both curative and preventive activities, which means it provides control once the infection starts and protects the soybean plant throughout the growing season at the same time. It provides excellent protection of the soybean plant and preserves the crop's yield potential. TOPGUARD™ has very good systemic activity, absorbs readily, translocates through the plant and protects new leaves as they emerge.
2. Why do growers need a fungicide like TOPGUARD™ when there are several other materials already available for controlling soybean rust?
   
   For one thing, the effectiveness of TOPGUARD™ has already been proven in areas where soybean rust is a serious problem. But TOPGUARD™ has several additional features that growers will like. For example, it is formulated in a way that makes it both easy to manage and easy on application equipment. This fungicide provides a very high level of rust control and plant protection. It also has good residual control of at least 21 days which, depending on the timing of infection, may allow growers to make only one application. And TOPGUARD™ has the ability to get into the plant quickly and protect young leaves very effectively. It can be tank mixed with other fungicides for late season diseases and even with insecticides and herbicides.
3. TOPGUARD™ has both curative and preventive properties. Why is that important to me?
   
   TOPGUARD™ does have both curative and preventative (some people say protective) properties. This is important because there may not always be an opportunity to apply a fungicide before soybean rust is visible. And while you can never let rust levels get very high, this is a disease that's sometimes hard to detect. But TOPGUARD™ will provide control when applied in a timely manner. And because it has systemic activity, it also protects the new, uninfected leaves as they unfold. So it's easy to see that you want a product that has both of these properties when you select a soybean rust fungicide.
4. Why is systemic activity important?
   
   Systemic activity is always important, but it is especially so with a disease like soybean rust. That's because soybean rust infections start at the bottom of the plant where the environment is most conducive to disease development. Once it develops, rust moves from the bottom to the top of the plant. Now, if you use a fungicide that only protects the outside of the plant, you will only control what's already there for about 14 days or so. But with a product like TOPGUARD™ that moves throughout the plant, you protect the leaves that emerge later, as well as any disease that was already present. This allows a longer period of control and your soybeans to reach their full yield potential.
5. What kind of residual control can I expect from TOPGUARD™?
   
   Based on data from Universities and other sources, growers can depend on at least 21 days of protection from a single application of TOPGUARD™. This long residual control, which TOPGUARD™ has, is important because, depending on the timing of the infection, it may save an application.
6. Does TOPGUARD™ offer good soybean selectivity?
   
   Yes, very much so. In the many commercial applications we've seen from flutriafol, the active ingredient in TOPGUARD™, in places like Brazil and Argentina, we've never seen any type of negative crop response. TOPGUARD™ is one of the most selective fungicides currently available for soybean rust, regardless of the soybean cultivar.
7. Why is there a single 7-ounce per acre use-rate for TOPGUARD™?
   
   The use-rate for TOPGUARD™ is 7-ounces-per-acre, although a grower can make two applications per season if necessary. Determining the correct rate is a matter of finding the critical level that offers the most effective protection of the plant, and at the same time giving adequate residual control. Based on our experience with TOPGUARD™, we've found 7 ounces to be the level that provides the degree of rust control needed, along with the amount of residual control a grower needs.
8. How many applications of TOPGUARD™ will a grower experiencing soybean rust likely have to make?
   
   Based on what we've seen so far, soybean rust generally infects the plant during the reproductive stage between early bloom or the R-1 stage, and full-bloom or the R-2 stage. That's when experts seem to think conditions are most favorable for rust to occur. If that's when the infection actually happens, and conditions are favorable for rust, you may need to make two applications, with the second one likely being at the R-4 or R-5 stage. Of course, if the infection happens later, say at full-pod or beginning of seed stages, then one application is probably all a grower would need to make. Fungicide applications made after the R-6 or full seed stage, generally won't provide much economic benefit.
9. When should a grower plan to apply TOPGUARD™?
   
   When and if soybean rust is observed, TOPGUARD™ should be applied as soon as possible regardless of the soybean's stage of growth. This is a disease that requires a lot of scouting, and even experts can have difficulty detecting soybean rust. The bottom line is that you need to spray as soon as possible whenever rust is detected in your soybeans, even if the infection is on as few as 2 leaves per 100. Soybean rust is very difficult to detect, especially in the early stages. Therefore, I recommend that growers keep in close contact with the Cooperative Extension Service for the latest recommendations in their area.
10. Should growers be concerned about soybean rust resistance to fungicides?
    
    As with any pesticide, there is always the potential for resistance to develop, though with TOPGUARD™, the risk is low. Growers should be aware that if they continue to use a fungicide with the same mode of action over a long enough period of time, there is the potential for resistance. This is true for all products including insecticides and herbicides. TOPGUARD™ can be tank-mixed with other fungicides having different modes of actions help reduce or delay the likelihood of resistance.
11. Why is the timing and effectiveness of the first spray so critical?
    
    It's the same as if we were talking about weeds in a crop. It is very critical to control those weeds as early as possible to get the best control and to eliminate competition with the crop. It's the same with soybean rust. This is a disease that must be controlled early because it has the potential to significantly impact yields. That's why it is vital that the first application be made in a timely manner and with a fungicide like TOPGUARD™ that provides effective control and good protection for the new leaves and pods.
12. At what stage is a grower most likely to observe soybean rust in his crop?
    
    Most data indicate that soybeans are most susceptible to soybean rust at the time they start the reproductive process, or about the time they start blooming until full-bloom. Of course, there have been instances in Brazil where they have seen rust much earlier than that. But I think in the U.S., rust is most likely to hit in this timeframe, at least from what we know right now.
13. Is there a threshold of infection severity that signals when it's time to spray for soybean rust?
    
    Scouting is very important because soybean rust can be difficult to identify in the field. But if you do have an infection, and haven't been able to identify it or apply a fungicide, your crop can be devastated within a two week period. I would say that anytime you have between 2 and 10-percent incidence of rust, that is 2 or 10 leaves out of every 100 with a lesion, you should make an application of TOPGUARD™. I would advise growers to use the soybean Sentinel plots in their area as a tool to facilitate the timing of a soybean rust application.
14. What weather conditions are most likely to be conducive to soybean rust?
    
    Moisture seems to play the largest role in allowing Asian soybean rust to develop in a field. Rust needs six hours or longer of extended moisture on the leaf over a period of a few days or weeks to develop. Temperature also plays a role, but apparently not as large a role as moisture. Research indicates that the optimum temperature for rust development is somewhere between 68 and 77 degrees F. However, this doesn't mean rust won't develop when temperatures are outside this range.
15. Does soybean rust reduce seed viability in effected soybeans?
    
    Soybean rust can have an effect on seed, because if you have rust at a level that affects the growth and development of the plant, that's going to impact the quality of the seed it produces. The result can be lower seed viability and germination.
16. How does a grower go about scouting for soybean rust?
    
    Since scouting is so very important with this disease, growers need to rely on the tools that have been developed by our Cooperative Extension Services. In the last two years, the individuals in the Extension Service in all the states have done an outstanding job of developing techniques that allow us to detect soybean rust before it becomes a factor in a grower's field. The Sentinel plots are one good example, so make sure you keep in contact with your Cooperative Extension Service and know what's going on with these plots in your area. Also be sure you know exactly how to look for soybean rust. Remember that it comes in low on the canopy and you'll need a good 20X or 30X lens to see it. But make certain you know what you're looking for because there are a lot of diseases that look similar to soybean rust, especially early in the development.
17. What should growers know about applying TOPGUARD™ to their soybeans?
    
    First of all, growers will find that TOPGUARD™ is a fungicide that's easy to handle and use. It's a good formulation that's easy to manage from an application standpoint. TOPGUARD™ mixes well and we've not seen problems with clogged nozzles. We've also not seen the need for adjuvants or surfactants to be added to spray. And TOPGUARD™ is compatible to be tank mixed with most insecticides and herbicides that are used in soybean production and can be easily applied by either ground or aerial applications. We suggest growers use 10 gallons of water per acre in ground applications and 5 gallons when applied aerially. Use nozzles that deliver medium sized droplets to minimize drift and get the spray down into the canopy. The bottom line is that TOPGUARD™ delivers the kind of control you need to maintain the yield potential of your soybeans.
18. Is ground application better than aerial?
    
    It really doesn't matter which application method you choose because both ways work well for TOPGUARD™ applications. As long as you use the recommended nozzles (ones that deliver medium sized droplets) and volumes of water (at least 5 gallons by air and 10 gallons by ground) you'll get the level of control you need from TOPGUARD™. So just use the method that works best for your particular operation.
19. Can I tank-mix TOPGUARD™ with other materials?
    
    Certainly. In fact, TOPGUARD™ can be tank-mixed with other fungicides, and any insecticide or herbicide that is commonly used in soybean production. If a grower has any concerns about mixing a particular material with TOPGUARD™, he should contact his dealer or a Cheminova representative for more information.
20. Will soybean rust likely be a big issue for U.S. growers anytime soon?
    
    This is a question that is difficult to answer. I don't think anyone can predict exactly what kind of problem U.S. growers will incur from soybean rust. But rust is definitely here in this country, and so is the potential for the disease to spread. But because it is so weather-related, predicting wide-spread distribution of the spores in exact locations is almost impossible. But because we know the disease is present, we can predict that if conditions occur that support wide-spread spore distribution, we can certainly have a problem. So we must be prepared with materials like TOPGUARD™ that can provide the level of protection from the disease that producers must have.
21. How easy is it for soybean rust spores to over-winter and remain viable?
    
    In the U.S., kudzu is the primary plant that serves as a host to the disease. In areas were kudzu can retain at least some living tissue throughout the winter, there is good over-wintering potential. This includes areas like Florida, southern Georgia and Alabama. Where temperatures are lower than 28 degrees F for a significant period of time, the probability of viable spores over-wintering is low. However, the question is how fast and effectively the viable spores that do survive can move via wind currents to different locations. We've seen in Brazil that, at least there, it can and does move rapidly when conditions are right.
22. How long has flutriafol, the active ingredient in TOPGUARD™ been used, and on what crops is it registered?
    
    TOPGUARD™ has been approved for use on US soybeans under emergency exemptions in 19 states. Flutriafol has been in use in more than 60 countries since the early 1980's. It is not yet registered in the United States, but it is registered in other countries on many other crops including wheat, grapes, apples and many others where it has been consistently effective against fungal diseases. This proven track record of effectiveness is the reason we have so much confidence that TOPGUARD™ is an effective tool against soybean rust.
23. Does Cheminova plan to register TOPGUARD™ for use in the U.S.?
    
    Yes. In the U.S. we are hoping to obtain soybean and apple registration, and also are looking at TOPGUARD™ for potential use on grapes, wheat, peanuts and several other crops. While the work we've done so far looks very promising, we will of course, go through the normal company and EPA review processes before any registrations happen.
24. How much damage can soybean rust really do to my soybeans?
    
    Soybean rust is a significant disease that can destroy a soybean crop. In fact, from a soybean disease standpoint, this one is unmatched by any other disease that U.S. growers have seen before. In situations where soybean rust is present and not controlled, yields have been reduced by as much as 90-percent. This is a disease that growers have to take seriously. And anytime there is any sign of soybean rust present, soybean growers need to take immediate action to control it.

TOPGUARD™ has been approved for use on US soybeans under emergency exemptions in 19 states.