Considerations for Soil-Applied Herbicides

Mark VanGessel, Extension Weed Specialist;

Planting any summer crop without a preemergence herbicide is a real risky proposition. Preemergence herbicides should be used in almost all situations. But what type of preemergence herbicide program should you use? A number of factors go into this decision; but cost should not be your number one consideration. An inexpensive herbicide program that does not provide effective control for your situation is going to be expensive in the long run.

Effectiveness is the number one criteria. Consider what are your common and problem weeds and select the herbicide(s) accordingly. This does not mean that you need to select an expensive herbicide, but you want to be sure you have the right active ingredients for your needs. Is your postemergence herbicide program highly effective and are you confident you can get to this field in timely manner? If the answer is yes and yes, then you can factor this into your decision. Otherwise, you may need to include “a little extra insurance” with your preemergence herbicide.

When are you putting out your preemergence herbicides? Usually with conventionally tilled crops these herbicides are applied within a few days of planting, but with no-till these herbicides might be applied 2 to 3 weeks before planting. Some herbicides remain active longer than others, but all soil-applied herbicides are only effective for a matter of weeks (not months). If you want to get 5 to 6 weeks of residual control you need to select accordingly, just be aware that few herbicides will provide effective control for this long.

Speaking of herbicide longevity, what are you going to planting into the field this fall or next year? Is herbicide rotation going to be an issue for you?

Have you thought about resistance management? Do you have species that are prone to developing resistant populations? Are you rotating your herbicide mode of actions, so you are not relying on the same ones? Weeds are resistant to soil-applied herbicides as well as postemergence herbicides and so you need to think of a herbicide resistance management beyond a single application or single season to be sure you are not setting yourself up for problems down the road.

Do not think of your soil-applied herbicide in isolation, think of it as part of a program and select the herbicide(s) that best fit your situation. And what works for your neighbor may not work for you.