By Brian Hefty
As soon as you saw the title to this article, you probably thought, “Wait a minute. I haven’t even sprayed soybeans for the first time. How can it be late?”
The main reason I call it late is because if you want to spray Flexstar or any product containing fomesafen, there is a 10 month rotational restriction to corn. In other words, if you want to plant corn April 10 next year, June 10 is your last day to apply Flexstar.
Another reason it is already starting to get late is if you want to apply another residual-only herbicide, since we like to see that done shortly after emergence. For example, Warrant, Outlook, Zidua, and Dual (all Group 15 herbicides) are popular choices to extend your pre-emerge residual control. In a heavy weed pressure situation, using pre-emerge herbicides may not be enough, so adding one of these Group 15s gives you better late-season control for less than $10 per acre. Since the Group 15s have zero burndown activity, they need to be sprayed before weeds emerge, as they need a little time to get rained in.
Did you know that volunteer corn can host corn rootworms, in effect negating the “rotation” advantage of planting soybeans? If you have volunteer corn, you need to spray it almost as soon as you see it. Weed for weed, volunteer corn is the worst yield-robber there is. It may already be getting “late” to spray volunteer corn if you want fewer rootworms in your corn next year. It only takes rootworms in the Midwest about a month to go through that “worm” stage of their life cycle. If they have no host (like corn roots) when they hatch, usually in late May or early June, they will die in a few days. That’s the goal, so spray volunteer corn early.
In terms of nutrients, it’s probably also “late”, even though soybeans don’t take up most of their nutrients until July or August. Yes, you can foliar feed, but if you need big amounts of fertilizer to achieve huge yields, it’s hard to apply that after planting and get good uptake. The reason why is the relatively small root system of the soybean plant. They say that on average, a soybean plant’s root mass is about one-fifth the size of corn. Unless you have very high soil fertility levels or place your fertilizer right where the roots will grow, it’s hard to apply lots of fertility this late and have it get used by your crop this year.
When it comes to controlling most diseases and insects, it’s still on the early side. We’ll talk next month in more detail about fungicide and insecticide use in soybeans, but if you have harmful insects or diseases in your field now, you may have to spray now. In most cases, the earliest we see spraying pay off is at R1, first flower.
Soybean yields have been on the rise the last few years, so do what you can to protect your income potential. Spray timely, and always address issues on the early side, rather than being too late.