Fungicide Call Proved Tricky on Corn This Year

To spray or not to spray- not that easy!

Published on: Aug 14, 2008

Spraying fungicide on corn is still relatively new, and while the window has likely passed for most fields this season, this issue will continue if and until more conclusive, uniform data comes along, either showing that fungicide applications pay or don't pay.

The best answer so far seems to be that odds of getting a return are best in years with heavy disease pressure and then only on certain hybrids. But even then, the decision of whether to spray or not is complicated, at least if you're trying to decide if those dollars will really be a good investment or not.

Here's this year's scenario, illustrating why the call can be a tough one. "The main disease problem we've seen, at least in central and north-central Indiana, is common rust," says Ben Grimme, team sales leader for Beck's Hybrids, Atlanta, Ind. Normally, common rust only appears in significant quantity in commercial corn once or twice in a decade. It may show up more frequently in southwest Indiana. Sometimes growers there also deal with southern rust, although it isn't a problem that far north every season.

Don't be misled- rust is often a problem on seed fields. It may be severe enough to justify spraying. But it's just rarely bad enough o trip the threshold for spraying commercial corn, simply for the rust alone.

"What it can do though is set up corn for stalk rot," says Kevin Cavanaugh, Beck's research director. "Stalk rot could cause significant yield damage if it causes enough lodging to increase harvest losses."

That means just writing off common rust in corn might not have been the best move out of hand, he notes. Instead, you needed to ask more questions. "That's where it gets tricky," Cavanugh says. "Some hybrids susceptible to rust are very resistant to stalk rots. So it still might not have paid to spray just for that reason."

However, there are hybrids that might exhibit common rust, but that also might be susceptible to one or more potentially serious stalk rots. That's when the appearance of significant rust in commercial corn fields might have led to justified decisions to spray a fungicide, he adds.

Earlier in the season, it appeared like this might be a bad foliar disease year. But what's missing to date is the heat. This season is unfolding as a cool, wetter-than-normal one over much of Indiana. In some ways it resembles 1992, when it was cool and wet, and yields were very high, but corn came out of the field very wet. In other ways it resembles 1981, when a wet spring delayed planting, and corn was again very wet at harvest. Yields were average, more or less. Spraying fungicides on corn wasn't a common practice then, so there's no data base to compare back to see how decisions to spray or not to spray might have played out in years with somewhat similar weather patterns to this season. Neither of those seasons featured huge floods, like those that occurred this year. That was the 1993 season, but it was confined to the western Corn Belt. Big floods didn't hamper Indiana farmers that year.

Put all that together and what you have is that 2008 will go down as a unique season. A few farmers who have gotten just the right amount of rain, and who got rain this past two weeks when crops started to need it, will remember this as a good year. Others will likely put it down as a year to forget, at least in terms of weather and growing crops.