Brassica Food Plot Weed Control: The Weeds You Cannot Spray

There is a specific, unfixable problem in a brassica plot, and University of Georgia Extension states it in one sentence about canola: no herbicide available for use in conventional canola will control either wild radish or wild mustard.

Wild radish and wild mustard are brassicas. So are your turnips, your rape, your kale and your radishes.

The weeds you most want to kill are the ones that most resemble the crop — and selectivity needs a difference to work with.

The Six To Eight Week Window

Start with the good news, because it changes what the rest of the job is for.

UGA’s canola bulletin notes that the crop generally shades the row middles in six to eight weeks, and after that period “canola is extremely competitive with weeds.”

You are not defending a plot for a season. You are getting it through about two months. After the canopy closes, the crop is doing the weed control itself, for free, better than any product you could have sprayed. Weeds that appear afterwards are mostly cosmetic.

Which means every decision that matters is made early — and most of them are made before the seed is in the ground at all.

Nothing Selective Kills A Mustard In A Mustard

Selectivity is not magic. It works by finding a difference between the crop and the weed big enough to exploit — a metabolic pathway, an enzyme the herbicide binds to, a rate of conversion.

Close relatives do not offer one. UGA’s list of what is labelled for conventional canola in Georgia is short: “trifluralin … clethodim … sethoxydim … quizalofop.” One soil-applied product, and three grass killers. For broadleaf weeds in a broadleaf crop of the same family, there is nothing.

This is the same trap as a clover plot, arriving from the opposite direction. In clover the crop is a legume and ordinary broadleaf herbicide kills it, so 2,4-DB exploits a slow metabolic conversion to squeeze selectivity out of a narrow difference. In a brassica plot facing a wild mustard, the difference is narrower still — and no product has found a way through it.

Canola is Brassica napus. So is the forage rape in your food plot bag. Turnip is Brassica rapa, kale is Brassica oleracea, and the wild mustard and wild radish that colonise disturbed ground are in the same family as all of them. This is not a gap in the market that a better product will fill. It is a botanical constraint.

Grasses Are The Easy Half

Everything that is hard about broadleaf weeds here is easy about grass weeds, for exactly the same botanical reason in reverse.

Clethodim is an ACCase inhibitor. Grasses have the target site; broadleaf plants do not. So a rate that removes crabgrass, foxtail and volunteer cereal from a plot leaves turnips, rape and kale untouched.

Two things decide whether it works.

The adjuvant is the first and the one most often skipped. Most clethodim labels call for an oil-based adjuvant rather than a plain nonionic surfactant. Reaching for the surfactant you already own is the standard reason a clethodim spray browns the grass and then lets it recover.

The label site is the second. A product labelled for canola is not thereby labelled for a wildlife turnip plot. UGA’s list describes canola grown as a crop in Georgia — useful for understanding what the chemistry can do, not a permission slip. Buy the product whose label names food plots or names your crop.

And whichever you use, coverage decides the outcome as much as the choice does. Our sprayer guide covers the calibration; the short version is that pressure and nozzle move your applied rate more than the pump ever does.

The Control Happens Before You Plant

This is the spray with real chemistry behind it, because before the crop exists nothing has to be spared.

Michigan State University Extension’s guidance for seeding brassicas into grass sod is to suppress it with glyphosate two to three weeks before planting. The interval is doing work: a systemic needs time to move down into the roots, and drilling into vegetation that is wilted rather than dead means your seedlings race something still alive — and lose, because it is established and they are not.

Since there is no in-crop broadleaf option, a broadleaf weed you do not kill now is one you keep all season. That is a harder deadline than a clover plot faces, and it is the reason this article spends more space on the seedbed than on the sprayer.

A note on the second product in that MSU sentence. Michigan State names one other herbicide for suppressing sod. It is a Restricted Use pesticide requiring a certified applicator licence, it is lethal in very small quantities if swallowed, and there is no antidote. We do not cover it anywhere on this site and we are not going to start here.

If the ground you are converting is established lawn or pasture sod rather than an old plot, how to kill a lawn before reseeding covers confirming a complete kill before you commit seed to it.

Seed Depth Is A Weed Control Decision

Brassica seed is very small, and small seed cannot be planted deep.

UGA’s instruction for canola is a quarter to a half inch deep in a clean, firm seedbed. Michigan State’s figure for forage brassicas agrees: no deeper than half an inch.

Three consequences follow, and all three are about weeds.

1. You cannot bury the problem. On a crop planted half an inch down, you are not turning soil deeply enough to bury a weed seedbank away from the surface. Whatever is in the top inch is competing with your crop from the same starting line.
2. A rough seedbed produces a thin stand. Broadcast seed that lands in clods or loose fluff makes poor contact and germinates unevenly. Mississippi State’s Southeast guide puts brassicas at about 5 pounds per acre drilled and 10 broadcast, planted September 1 to October 15 — the broadcast rate is doubled precisely because contact is worse.
3. A thin stand never closes the canopy. Which returns you to the six-to-eight-week window and removes the free weed control waiting at the end of it. This is the failure loop: rough bed, thin stand, open canopy, weeds all season, no product available to fix it.

Our food plot seedbed guide covers the liming and soil work that has to start months earlier, and it applies here with more force than it does to a legume plot, because here the seedbed is most of your weed programme.

The soil-applied product UGA names for canola is trifluralin, incorporated before planting. Trifluralin and pendimethalin are both dinitroanilines and they are not interchangeable: the consumer pendimethalin on a lawn shelf is labelled for turf and ornamentals, and a wildlife brassica plot is neither. Given that the seed sits a quarter inch down in the same layer the herbicide occupies, crop safety here depends entirely on the label naming the crop.

The Short Version

A brassica plot gives you a grass herbicide and a deadline.

Kill everything before you plant, because that is the last time selectivity is not your problem. Plant shallow into a firm, clean bed at a rate that closes the canopy fast. Spray clethodim, with an oil adjuvant, if grass comes through.

And accept the one thing that has no answer: a mustard growing in a mustard plot stays.