An integrated pest management approach is key for managing field crop diseases, which requires scouting, host resistance, crop rotation and using the right fungicides in a timely manner to succeed.
Speaking at the virtual North Carolina Crop Protection School, Lindsey Thiessen, North Carolina State University Extension plant pathologist, said both a whole-farm perspective and long-term management is critical.
Job one in disease management is scouting. Thiessen said successful scouting requires you to get out of the truck and “getting up close and personal” in looking for pathogens. She emphasized that diseases are not evenly distributed or simply found on the edge of the field.
“When I say ‘getting up close and personal’ that means different things for different pathogens. For foliar diseases, we want to start looking at the bottom of the canopy. And we do that because the lower portion of the canopy is very humid, very warm, and that’s conducive for most of our foliar diseases. That’s where they are going to start first. If we think about things like rusts, they’re going to be in the lower portions of the canopy,” Thiessen said.
Equally important as effective scouting in managing the soybean cyst nematode is a good rotation where non-host cultivars are included. Thiessen advises a year with a non-host followed by a resistant crop then another year with a non-host cultivar. After that, you can plant a susceptible variety that has the agronomic characteristics you want.
“In places where we don’t have host resistance available, we would want at least two years away from soybeans before we plant there again,” Thiessen advised, stressing this is critical for limiting soybean cyst buildup.
She emphasized that disease inoculum buildup is limited when rotations include non-host crops.
In the meantime, Thiessen said continued reliance on fungicides, nematicides and insecticides is creating a big problem of pesticide resistance. “We don’t necessarily see a whole lot of influx of new modes of action and that is going to limit us in what we can do in the future,” she emphasized.
For example, frog eye leaf spot was discovered to be resistant to strobilurin across North Carolina in 2011. Thiessen said resistance tends to be most heavy in parts of the state where there is a heavy reliance on a single mode of action to control diseases.
Thiessen said farmers need to turn to alternative options for managing disease, and they need to use other fungicides, beyond group 11, which is the most common group for managing soybean diseases. “When we are looking at rotating chemistries and picking out modes of action, we want to make sure we avoid those group 11s, those strobilurins, because they are not going to be very effective for us,” Thiessen advised.