Roundup and all glyphosates are way down in price, as is 2,4-D, dicamba, and just about anything else you want to use for a fall burndown!

Here are some of the most commonly asked questions about burndowns at this time of year, along with my answers. Most importantly, do not let weeds go to seed or you could be fighting them (and spending a lot of money to do so) for many years.

Can’t I Just Use Tillage Instead of Spraying a Herbicide?

Absolutely. We use tillage on our farm, too. While tillage has advantages, including how no weed is resistant to iron, it does have several drawbacks. You will have more erosion, slightly lower organic matter levels, use more fuel, take more time, and catch less snow over the winter.

Do I Need a Post-Harvest Burndown?

If there is a chance weeds will go to seed prior to the weeds being killed by frost this fall, then a burndown is important. You don’t want to fight massive weed populations in the future.

Do I Need Residual Control?
Or Should I Just Worry About Burning Down What Is There Today?

Here again, this depends on how long you have until winter kill does its job. If that won’t happen for a long time, adding a residual herbicide may save you a second trip across the field. You could also consider using enough product so you gain some early spring weed control. For example, people who have used fall Valor or Fierce have loved the clean fields they typically have through May and into June.

Which Product(s) Should I Use?

Post-harvest, I almost always suggest having Roundup/glyphosate in the tank, because even though there are resistant weeds, the vast majority of weed species can still be controlled with Roundup, and it’s super-cheap this fall. Adding Distinct, my favorite fall burndown product, will eliminate pretty much all broadleaves. Distinct is Status without the corn safener. Residual is short, so carryover shouldn’t be a concern, and Distinct is far superior to straight dicamba or 2,4-D. If you want to add residual, Valor is my favorite product because you can rotate to many crops, but there are a number of other choices depending on your target weeds and crop rotation. In the fall we’ve used Group 15 herbicides, HPPDs, yellows, PPOs, and just about anything else that has residual, all with good success.

Do I Need Spray Adjuvants?

In a hot, dry growing season, weeds develop a thick, waxy coating on leaves. In order to better penetrate that wax and deliver the herbicide to the growing point(s), the use of crop oil or methylated seed oil is usually very beneficial. When you aren’t worried about damaging a growing crop, you can ramp up your adjuvant choice and rate to achieve better weed control. Ammonium sulfate is another product that can help, too, as well as other water conditioners like Water-Rite that tie up hard-water ions and lower spray solution pH.

What Rate(s) Should I Apply?

You need to spray a high enough rate to control your weeds. Since Roundup is so cheap, keep the rate up, especially if you are after perennials. With Distinct, use 6 ounces. With dicamba, you can use 1 quart instead of the 1 pint in-crop rate if you have tough-to-control weeds like marestail or dandelions. In terms of 2,4-D or anything else, just make sure you use a dose that doesn’t leave half-dead weeds out in the field. In terms of residual herbicides, use the maximum rate. For example, in the fall we recommend 4 ounces of Valor instead of the 2 or 3 ounces you usually apply pre-emerge in the spring.

Will What I Spray Impact a Cover Crop or Next Year’s Cash Crop?

First of all, let’s be clear about what a “cover crop” actually is versus a “cash crop”. If you are baling, grazing, or in any way gaining income off your “cover crop”, that’s not a cover crop. That’s a cash crop. A cover crop gives you zero short-term economic benefit. Personally, I don’t care much about residual herbicides hurting true cover crops because if weed control is better in your cash crop, you will make more money. If you are going to bale or graze a crop yet this fall, then by all means be careful about what you will apply in your burndown. As much as I love having residual herbicides in my burndown, products like Valor will kill or damage most cover crops if seeded soon after the Valor application. Sharpen is one of the few residual herbicides labeled pre-emerge for small grains and a few other grass cover crops, so that could be an option for you instead. Roundup has no residual, but even dicamba, 2,4-D, and Distinct have enough residual to hurt many cover crops for a week or two, so be careful about what you apply and when.