By Peter Johnson, RealAgriculture agronomist
Many producers can’t wait to put the 2018 corn crop behind them. Despite big yields — even record yields for some growers — mycotoxin levels in the crop has turned harvest into a nightmare. And that’s not to mention the constant downpours and totally saturated fields that will likely make the balance of the harvest a muddy mess.
But let’s look at seven things that played (and maybe didn’t play) a large role in this DON mess. Some things that happened we absolutely expected, but there are a number of trends and observations we could not have predicted. Here is a summary of what we think we have learned to date (all subject to revision, of course):
Weather: Mother Nature is still the driver. There are clean areas, and there are severely impacted areas. Welcome to the world of Fusarium graminearum (Gibberella zeae).
Genetics: We are seeing huge differences between varieties. Disease resistance is an incredibly tough problem, but seed providers MUST do more to figure out the genetics. We simply cannot accept weather and the complexity of the disease as acceptable excuses moving forward.
Planting date: We would have expected that late planted corn would have been far worse for DON. It should have silked and pollinated after the rains started, prime for infection. But not so! Corn planted in the May 8-11 window is often much worse than corn planted later in May. The early corn had mostly tasselled and silked prior to the rain, yet it has higher DON levels. It is almost as if the early corn was so stressed that when the rains hit, defences were weakened and it was more susceptible. Not the result we expected.
Husk cover is the main driver. Smaller cobs that the husk “glued” itself to are all bad news. Further south, cobs that stood upright and grew out the husk, allowing bird and insect damage, are problematic. What we need? Cobs with loose husks that turn down.
Stressed areas are generally worse, as expected. Headlands and stressed areas are often showing higher DON. One field was reported at 8 ppm on the headlands, 1 ppm in the field.
Planting issues: We think that late emerging plants are adding to the problem. They have smaller cobs and are more likely to have tight husks (no data yet). In some cases it may be the refuge hybrid, but doing the perfect job and having uniform emergence certainly won’t make this problem worse!
Testing: DON testing at the elevator is incredibly unreliable. In fact, it is so bad that I wrote an entire article on it.
Fungicide: Spraying results were variable. We have a long way to go here. Many growers sprayed corn with a fungicide, but one that offers NO control of gibberella, and then wondered why they had a problem. Even those that sprayed fungicides that give suppression (Caramba, Proline) did not always reduce DON levels. It was simply so wet, so warm, so humid for SO LONG that the fungicide protection ran out.
Cleaning: WOW! Fines are the issue. Whenever we test fines, they are three to six times higher in DON. Get rid of them! Combine setup is key. Maximum wind, screens to let fines out EVERYWHERE, close the back half of the chaffer sieve. See more on combine setup in this video
Rotation: Lots of questions around corn after wheat. To date, there are no good examples of corn after wheat being worse. There are reports of corn on corn being worse, but not corn after wheat. And the yield benefit is real, with some growers reporting up to 40 bu/ac higher yields on corn following wheat vs. corn following soybeans. Keep growing wheat.
Tillage: Again, many producers wondering if less tillage is part of the issue. There simply is no consistency. Tillage does not solve this problem.
So, how do we avoid this ever happening again? There are no easy answers. The best answer we have is we need good genetics and to use effective fungicides together — not just one or the other. Planting perfection, combine setup, and rotation are all things that will help, but not avoid the issue. It’s not a great answer, but until we can understand this disease better, it’s simply all we have.