Southern soybean growers face a laundry list of nearly two dozen different diseases, some major, some minor, but all capable of reducing yields under the right conditions.
The farmer whose production system includes disease awareness and management is not as likely to be confronted with a disaster as the one who pretty much lets the crop take care of itself, specialists said at a recent soybean field day.
“A bushel lost to this disease, a bushel lost to that disease, and pretty soon it adds up,” says soybean breeder James Davis with Hornbeck Seed Co. at DeWitt, Ark. “One of the best things any grower can do is scout his fields; if he doesn't, when harvest-time comes he may wish he had.” Several diseases have been particularly bad this season in several Mid-South areas, he says.
“Conditions have been really conducive to frogeye leaf spot; I've seen fields that have lost leaves three weeks before maturity.”
Sudden death syndrome (SDS), Davis says, “can take every leaf, every pod off plants. Aerial blight can also take off every pod in a field. Stem canker can ruin a crop.
“I know of fields in Mississippi that have been ready to harvest for three weeks, but the leaves haven't fallen off because of phomopsis. By the time the leaves finally are off, those beans won't be good for anything but hauling to the dump.
“Last year, we heard a lot about soybean cyst nematode (SCN). This year, beans were back on a lot of those fields, with no problems — conditions just weren't right for them to cause trouble.”
Again, scouting is important, Davis says. “If you know you've got areas susceptible to SCN, pull up plants and check the roots. Spend $17 for a soil analysis to determine the race and then, next year, plant a resistant variety.”
Seed companies have varieties with resistance to various SCN races; varieties are also available with varying degrees of resistance or tolerance to several diseases.
“But if you don't scout, so you know what's going on in your fields, you won't know what you need when it comes time to buy seed the next year. It's like playing Russian roulette with your yield potential.”
Ronnie Helms, research agronomist for G&H Services at Stuttgart, Ark., told growers that the fungicide Quadris can be an effective disease control tool, particularly for aerial blight. “In studies since 1998, the least response we've seen is 2 bushels, the most 12, along with an increase in seed size and overall seed quality.”
Keith Driggs, technical support rep for Syngenta at North Little Rock, said 2001 was the first year for a full federal label for Quadris on soybeans, and “there's been a lot used this year. You can tell, to the row, where it was applied on a field.”
Most growers use a 6-ounce rate, which Driggs says, costs 3 to 3.2 bushels for the application. “Yield response has usually been more than enough to pay for it. Plus, you get the bonus of controlling other diseases such as anthracnose and phomopsis.”