MANAGING WHITE MOLD IN SOYBEANS
Four years ago, Frankie Kasowski III reviewed aerial imagery of potato fields at Kasowski Farms near Becker, Minnesota.
“Immediately, we started seeing emergence and seed placement differences between planters,” says Kasowski, who owns Kasowski Farms with his grandfather, Frank Sr.; father, Frank Jr.; and two brothers, Robert and Alex. “We could see which planters were not doing as good of a job as others. Even emergence with potatoes is no different than with corn. We want potatoes to emerge within two days. When that happens, we see a five- to eight- [100 pound] bag-per-acre difference between those fields and those that don’t emerge evenly.”
Differences quickly add up. A difference of five to eight bags at $10 per bag per acre equals $50 to $80 per acre. As a result, the aerial imagery caused the Kasowskis to replace ineffective planters.
The farm also found the aerial imagery could detect maladies such as plugged irrigation nozzles. So, the Kasowskis also began using it in their seed corn production and eventually also adopted aerial imagery in soybeans.
“We wanted to see what we could do to start pushing soybean yields,” says Kasowski.
The Kasowskis focus mainly on growing potatoes. However, they cannot grow potatoes on the same field annually, due to disease concerns. Thus, they rotate ground to corn and soybeans.
Soybeans, though, have one serious downfall in that they are susceptible to white mold as are potatoes. White mold thrives during periods of moderate temperatures and high humidity.
“White mold is a huge game changer up here,” says Kasowski of their farm northwest of Minneapolis. “I’ve seen soybeans that look beautiful – green, medium tall beans with no lodging. Then, they can fall just like that during an August with high humidity and cool temperatures. You can have 60- to 70-bushel [per acre] beans that become 40-bushel beans.”
Narrow rows or high seeding rates that spur a dense canopy also can exacerbate white mold outbreaks, says Sam Markell, North Dakota State University Extension plant pathologist. “Anything that helps keep the canopy wet, such as rain or long, heavy dew, is going to increase the risk of disease,” he says.
Fortunately, control measures exist. “There are some varieties that tolerate white mold better than others, but fungicides also are useful in managing white mold,” says Markell.
Aerial imagery plays a valuable role in tipping off Kasowski Farms to water stress issues that negatively impact crop health two to three weeks before the effects are visible to the naked eye. White mold, though, complicates irrigation and fungicide management of their soybeans.
“I love irrigation, but on soybeans, I hate it,” jests Kasowski.
Irrigation is needed on the higher sandy soils that predominate in this part of east-central Minnesota. White mold, though, thrives in low-lying areas of the field. Balancing these two extremes within a field is challenging.
“We end up starving our knolls [of water] on high ground to the wilting stage because our low ground is still saturated,” says Kasowski. This strategy helps to a point, as plants on high ground can sustain themselves for a short period on dew, he says.
Still, limits exist. “When our knolls start drying up, we turn on the center pivots,” says Kasowski.
Kasowski Farms also uses selective fungicide applications based on Ceres Imaging aerial imagery to curb the spread of white mold on low-lying soils. Guided by aerial imagery, the Kasowskis last year selectively sprayed low-lying 40 acres prone to white mold in an 85-acre field.
“It was just basically boom on, boom off,” says Kasowski. The combination of irrigation strategy and selective fungicide application worked well, he adds.
Fungicide application, though, is challenging. “Timing is crucial,” says Randy Myers, Bayer Crop Science agronomic solutions manager. For optimal control, a preventive fungicide must be applied when 80% of soybean plants are flowering during the R1 phase (beginning bloom), he says. Just a bit sooner or later compromises control, Myers adds.
Because white mold festers in the lower canopy, canopy penetration with the proper nozzle is key for optimal control.
“The most effective nozzle is going to change, depending on the degree of canopy closure,” says Markell. TeeJet trials show that when a canopy is no more than 75% closed, TeeJet nozzles that create fine droplets work best.
“As the canopy passes this point, medium droplets work best,” says Markell. “As the canopy reaches 90% to 100% closure, the most effective control and highest yield differences occur with coarse droplets.”
Optimal droplet size, though, may vary among the nozzles of companies. At high canopy closure rates, Wilger tests show the firm’s nozzles that produce very coarse droplets give better control compared with coarse droplets, says Markell.
Agronomist and crop consultant John Vaadeland sends Kasowski aerial images during the growing season that are based on factors such as normalized difference vegetation index (NDVI). NDVI readings allow users to identify healthy and unhealthy field areas. “My sprayer driver will comment that it matches up perfectly to low areas in the field that are prone to white mold,” says Kasowski. “Aerial imagery has just opened our ey