In the coastal areas southwest of New Orleans, La., Asian soybean rust is likely to pop up anywhere each and every spring. It's up to Blaine Viator, a Plattenville, La., consultant, to make sure that the disease does not cause economic damage for his clients.
Viator, speaking at the National Alliance of Independent Crop Consultants annual meeting in Seattle says soybean production plays an important second fiddle to sugarcane in Iberia Parish, where Viator consults. Over the years, sugarcane producers have learned that planting Roundup Ready beans once every four to five years can control the weeds that crop up in sugarcane.
While Asian soybean rust is a concern here, it's only one of several diseases that threaten soybean production. Others include pod and stem diseases and frogeye leaf spot.
“The area is so humid that soybean foliage often does not dry off at all during the day,” Viator said. “So we have more disease pressure than other areas. The worst thing we battle is cercospora leaf blight. We have not had much success at all controlling it. It concerns me much more than soybean rust, because I know I can control soybean rust.”
Viator noted that in south Louisiana, “it's not uncommon, especially when soybean harvest is delayed, to see poor quality beans even if the beans have been treated with a fungicide.”
There are some things growers and consultants can do to improve the efficiency of their fungicide programs, according to the consultant.
Viator said disease control can improve significantly when a drop tip is added to spray to the side and underneath the leaves. “Practically, we can only put out about 20 gallons of water per acre with the application, and we urge our growers to go with 60 to 80 pounds per square inch of pressure when we can.
“We do use twin-jet tips, and I have some growers who use flat fans. A lot of researchers are starting to say it doesn't matter what type of tip you use. But it's going to be hard to get fungicide from the top of the canopy down to bottom of the canopy without using a drop tip or an air induction system.
“I tell my growers to stay away from the drift-reducing tips that are becoming more and more common with Roundup applications.”
Viator's Iberia Parish is usually where rust pops up as the soybean-growing season gets under way. Usually it's on kudzu. “At first, we thought the disease could not overwinter in south Louisiana because our winters are a little too cool. We thought it could only overwinter in south Florida.
“We are not sure, but we think that rust is overwintering here, even though it may not be on kudzu. It could be overwintering on some winter weeds or on stems. But every year, we find it in the same kudzu patch in a very small location. When we have an extremely mild winter is when we're going to see the most carryover.”
When rust does explode on the scene, “it can be pretty scary when you see how fast this disease can build up. But one thing in our favor is that in south Louisiana, we were using fungicide applications before Asian soybean rust because of our intense disease pressure. So whether or not we have early detection isn't as crucial as it is in other places.
“But we've realized that (areas north of us) are relying on us to do this early detection, so you can make decisions on your fungicide applications.”
There are several tools to use in the field to help diagnose the disease, according to Viator, including Envirologix QuickStix, “which I use quite regularly. My growers love them. We could run the tests on the tailgate of the truck. They've also improved the product where the ‘positive’ line will be easier to see.”
Viator has tried using a 30X hand lens, “but I have given up on them altogether. I do use a cheap, portable microscope from Edmund Scientific for $130. It has its own light source.
“I've also taken a lot of digital photographs using the macro function and sent them to university and Extension. We coordinate pretty well now.”
Viator puts out his own soybean sentinel plots in addition to the 10 to 15 plots of the Louisiana Cooperative Extension Service. “I like to have the plots on my own clients' fields, and I can scout them regularly. The university has come to appreciate this. We really work together. I'll send them a map with GPS coordinates of all my locations.”
To prepare the plots, Viator uses a push-type garden planter to plant soybeans about three weeks before a grower plants his commercial soybeans. “I plant a few rows in a place that would be hard for them to spray or a place that I can manage. I like to put them by treelines. I can put out five sentinel plots in a day.”
Viator said that more research is needed to determine if there is value in spraying soybeans for soybean rust after they reach the R-6 growth stage. “We were told that once you hit the R-6 stage, there won't be economic losses from rust. We have had some situations when rust came in at R-6 right when the R-3 fungicide application wore off. And when it did, it blew up.
“R-6 is the longest growth stage in our beans, lasting almost five weeks. There are a lot of doubts that maybe at R-6, we're still not quite out of the woods yet. We did have some fields that we think affected us. But I can't say for sure that it was affecting yield that severely. We have to rely on the research for that.”
Viator noted that in 2007, “with the price of soybeans and the disease and quality issues we were having, because we found rust earlier than we ever have, we went with a strobilurin plus a triazole at two different timings, one at late R-2 or early R-3 and three to four weeks later, which we could do because of the price.
“We didn't find rust in any of our fields, even at full maturity, or R-7. In 2006, every soybean field I had, had full-blown Asian soybean rust on the lower part of the canopy.”