Beating yield-robbing diseases requires keeping an eagle eye on your crop throughout the growing season. But while scouting is important, disease management involves much more than burning shoe leather walking your fields. Strategic planning begins long before planting time, and it will make your scouting easier and more effective.
"Nowadays, almost all seed is sold with some degree of seed treatment already applied, so you can spend less time thinking about seed treatments," says Farm Journal Field Agronomist Ken Ferrie.
Use that time to think about which types of diseases you're likely to deal with. "If you have noticed seedling blight in past years, remember these are mostly water molds, driven by cool, wet soil conditions," Ferrie says.
"Planting in ideal disease conditions like that can sometimes offset the effect of a fungicide and the resistance that's bred into a hybrid. So don't push the planting date in fields with disease history when they're wet. If you can wait until the soil is drier, you will have fewer seedling diseases," he adds.If you're fighting seedling blight issues, plant hybrids with good early season vigor and rapid emergence, Ferrie adds.
Think about which disease risk factors exist in each of your fields. "We put a lot of weight on evaluating the risk and respecting it," Ferrie says.
Old-crop residue, left on the surface, while valuable for many reasons, increases the risk of disease. "Although a few of the diseases affecting adult corn plants blow in with the wind, 70% to 80% of them are carried over in last year's crop residue," Ferrie says.
Anytime you leave more crop residue on the surface, disease risk goes up. So if you're growing continuous corn, no-till would have the greatest disease risk, followed by strip-till, vertical tillage and moldboard plowing, in that order.
In a corn–soybean rotation, no-till still carries the greatest risk because disease spores can live in corn residue that is left on the surface from two years ago. Strip-till ranks second, followed by full-width tillage. "If you no-till your soybeans but do tillage ahead of corn, your risk factor is in between," Ferrie says.
"If you're growing continuous corn, which carries a higher corn disease risk, visit hybrid test plots," Ferrie advises. "If a continuous corn plot was not sprayed with a fungicide, it will give you a good comparison of hybrids and show you each one's weak links for disease resistance."
Understand what hybrid disease ratings can tell you about managing each field. "With individual hybrids, ratings tend to be excellent for one disease but poor for another," Ferrie says. "See if there is a ‘sweet spot' for certain diseases. If there is, you don't necessarily have to shy away from that hybrid; but you should plan to do additional scouting in that field and possibly apply a fungicide."
- March 2009