By Darren Hefty

Kochia has always been a tough weed in wheat country.  ALS herbicides like Glean used to be good until ALS resistance hit.  Roundup used to work great in burndowns, but now Roundup resistance is spreading quickly.  Starane has been the “go to” product for years; but in North Dakota, there is some kochia that NDSU says is resistant to Starane.  That is still a topic of debate, but I think you can see where I’m going here.  Weeds like kochia and others are becoming harder to control.  Even if you haven’t had a need for a pre-harvest burndown in the past, it may be something you need to do this year or in the near future.  There are options.  Also, post-harvest burndown (perhaps hand in hand with a cover crop for some farms) will be as important as ever this year.

PRE-HARVEST BURNDOWN

First of all, there are two categories here:

  1. Seed Fields – Pre-harvest burndown of weeds may be necessary in seed production to keep those weed seeds (especially noxious weeds) out of the seed.  Let’s talk about an old myth that says something like, “If you spray weeds before the seed is completely made, you might just get lucky and hurt the germination on them.”  From experience (and Murphy’s Law) I would say that your chances of hurting germination on weed seeds is slim and your chance of hurting germination on your wheat or barley is higher.  Timing is very important, as you should not spray until at least 10 days after heading (and this varies depending on the herbicide), and most products (like Roundup and Clarity) have a 7-day pre-harvest interval.  In fact, according to work done at SDSU, seed moisture needs to be down below 30-35% to minimize potential damage to seed germination.  Roundup is not recommended in seed fields because it has more potential for seed germination injury than others.  Another good tip is to spot spray rather than spray the whole field to minimize any potential risks you’re taking on.
  2. Non-Seed Fields – In this case, you’re not so worried about seed germination effects.  You’re strictly concerned about yield and harvestability.
    Herbicide choices include Roundup, Clarity, 2,4-D, Aim, and several others.  Roundup is best for grasses and many broadleaf weeds, but you can only use 22 ounces of RT3 or PowerMAX, so don’t expect a quick knockdown of weeds.  Eight ounces of Clarity can be used and works fairly quickly.  Up to a quart of Amine or four-pound Ester can be used, too.

POST-HARVEST BURNDOWN

After harvest, you have all herbicide choices at your disposal.  Your concern at this point is drift and crop rotation.  Roundup is pretty much a given because it controls more weeds than any other herbicide.  The tankmix partner becomes the real question.  Personally, I like to use something with a good deal of residual.  If you’re coming right back with wheat in 45 to 60 days, then you may consider Valor or Sharpen.

To just get more burn, typically the choices come down to what’s cheap.  Historically, that’s been generic dicamba or some form of 2,4-D.  There’s a little more residual control out of the dicamba and a little more kick on some of the tougher weeds like wild buckwheat, field bindweed, and dandelions.  I prefer to use a full pint.  Where crop rotations allow, Brian will push it to a quart where we have dandelions and other tough perennials or biennials.

GREEN BRIDGE – We saw mite problems this year in large areas of wheat production.  Mites need a living host to stay in a field, which is one of the big reasons we strongly recommend eliminating the “green bridge.”  Make sure nothing green is living in the field for two weeks or more ahead of seeding your next crop.

If weeds are a problem in small grain fields, a pre- or post-harvest burndown could be critical for you.  There are lots of choices and a number of considerations, so work with your agronomist on a specific recommendation for your fields.