When to Spray Roundup on Food Plots

Spray timing matters more than the brand on the jug.

I spray Roundup on food plots when the weeds are actively growing, the forecast gives me 6 to 24 hours with no rain, and daytime temps are sitting between 55 degrees and 85 degrees.

If the weeds are drought-stressed, frost-bit, or muddy-cold and not growing, I wait, because you are about to waste money.

I have sprayed plots in Pike County, Illinois where every mistake costs you two weekends and $127 in seed.

I have also sprayed on public ground in the Missouri Ozarks where you might only get one clean window before the forest turns into a green wall.

Decide if you are killing weeds or just buying time.

Most guys say “I’m spraying Roundup.”

What they really mean is they want a clean seedbed or they want to knock weeds back so their plot gets a head start.

Here is what I do when I want a clean seedbed for fall brassicas.

I spray once to kill what is there, wait until it is crispy, then spray again or lightly disturb the soil to trigger a new flush and hit it again.

That second pass is the difference between a plot that looks good on opening day and a plot that turns into a ragweed mess by October 10.

If you are just buying time until you can get back with a disc, then a single spray can be fine.

Just do not tell yourself it is “done” if you still have green stems waving at you a week later.

Mistake to avoid: Spraying right before rain because you are “out of weekends.”

I learned the hard way that Roundup does not work on my schedule.

Back in September 2014 in the Missouri Ozarks, I sprayed at 5:30 PM with storms coming at 9:00 PM, and I watched half the plot survive like I watered it.

My buddy swears by “two hours rainfast and you’re good.”

I have found two hours is the minimum on the label, but 6 hours is what keeps me from re-buying chemical and burning another trip.

If you are hunting public land and you drove 2 hours to get there, forget about “good enough” timing and focus on a clean weather window.

I would rather spray one week later with a dry forecast than spray “today” and do a half-kill.

Decide based on temperature, not the date on the calendar.

Roundup works best for me when it is warm enough for the plant to be growing and moving sap.

My sweet spot is 60 degrees to 80 degrees during the day with nights above 45 degrees.

If it is 42 degrees at daylight and the high is 54 degrees, I still spray if the weeds look perky and green.

If it is 94 degrees and everything is wilted at noon, I spray at 7:00 AM and quit by 9:30 AM.

I learned the hard way that drought-stressed weeds are a money pit.

In August 2020 on my Pike County lease, I sprayed during a dry spell, and the foxtail just shrugged and came right back.

Two days after a half-inch rain, I re-sprayed and the same patch died in five days.

Tradeoff: One heavy spray now or two lighter sprays that actually work.

Guys love to “burn it down” with a hotter mix.

The tradeoff is you can scorch leaves fast and still not kill the root if the plant is stressed or too mature.

Here is what I do for most food plot kill-down.

I mix to the label rate, add ammonium sulfate if my water is hard, and I focus on coverage instead of trying to create napalm.

If the weeds are knee-high and waxy, I would rather spray, wait 10 days, then hit the survivors again.

That costs more in time, but less in replanting and frustration.

Make the call: Spray before you till, or skip tilling and spray twice.

I grew up poor and learned to hunt public land before I could afford leases, and that taught me to do things the cheap way that still works.

Skipping passes with equipment is usually the cheapest “upgrade” you can make.

If I am doing a no-till or throw-and-mow style plot, I spray first, then I plant into dead thatch.

If I am going to disc, I still spray first if the plot is thick, because discing green weeds just spreads them and makes a mess.

But if the plot is already mostly bare dirt with a few weeds, I will lightly disc, let the weed seeds sprout, then spray that new flush.

That is the best way I know to get ahead of pigweed and ragweed without living on a tractor.

Mistake to avoid: Spraying after you mow, then wondering why it did not kill.

I learned the hard way that mowing can save weeds.

Back in July 2016 in southern Iowa, I mowed a clover patch low, sprayed the next morning, and most of it came back.

The plant had less leaf area to drink the herbicide, so it lived.

Here is what I do now if I have to mow.

I mow, wait for 6 inches of new green growth, then spray on a warm week.

If I have enough leaf to spray before mowing, I spray first, wait 7 to 10 days, then mow the brown down.

Decide what weeds you are actually fighting, because it changes timing.

Grasses and broadleaves do not always die on the same schedule.

Foxtail and crabgrass can take longer than you think, especially if they are headed out and mature.

Young broadleaf weeds die quick and make you feel like a hero.

Then the grasses survive, and your seedling plot gets choked later.

Here is what I do when I see mature grass with seed heads.

I spray early morning after a decent rain, and I plan on a follow-up spray or a second tactic like mowing later.

If you see glossy, waxy leaves on weeds, forget about “a quick pass” and focus on spray coverage and a second check in 7 days.

My Quick Rule of Thumb

If weeds are green and growing and the forecast shows 6 to 24 rain-free hours, spray Roundup that day.

If you see wilted leaves at noon from drought or heat, expect a weak kill, and wait for rain or spray at daylight.

If conditions change to cold nights below 40 degrees or a first frost, switch to waiting for the next warm spell or plan a mechanical reset instead of wasting chemical.

Tradeoff: Spraying for deer attraction versus spraying for plot success.

I have watched deer browse a weedy plot like it was a salad bar.

I have also watched the “weeds are deer food” idea turn into a plot that never establishes and feeds nothing in November.

If my goal is a fall kill plot in Kentucky-style small acreage, I want clean and simple, not a science project.

If my goal is a summer snack plot on a corner of my Pike County lease, I might leave a strip weedy on purpose for cover and browse.

If you are hunting pressured ground like Buffalo County, Wisconsin public edges, forget about making your plot “pretty” and focus on making it huntable with cover nearby.

Deer do not walk across open dirt at 6:30 PM just because your clover is perfect.

Here is what I do for spring plots versus fall plots.

Spring plots punish late spraying because weeds explode once the sun gets strong.

Fall plots punish early spraying because you get a second weed flush before planting.

For spring planting, I spray as soon as I have consistent 60 degree days and a dry window.

Then I plant as soon as I see the weeds yellowing, because spring moisture is a gift.

For fall planting, I like a two-step.

I spray 3 to 4 weeks before I plan to seed, then I spray again 7 to 10 days before seeding to catch the new flush.

This connects to what I wrote about deer feeding times because a plot that establishes on time changes daylight movement fast.

Mistake to avoid: Thinking more scent control matters more than weed control.

I wasted money on $400 ozone scent control that made zero difference.

I should have put that money into seed, lime, and a second spray.

Deer live with farm smells and diesel all the time.

They do not live with a plot that fails and turns into a jungle.

If you want to understand why deer pick certain foods over others, start with what I wrote about best food plot for deer because the crop choice changes how strict you need to be on weed control.

Decide if you are doing this with a backpack sprayer or an ATV boom, because that changes your day.

I have done it both ways, and I still use a backpack on small kill plots.

Coverage is king, and a cheap setup can still work if you are careful.

Here is what I do with a backpack sprayer.

I mark my lanes with flags, I keep steady pressure, and I walk the same pace like I am mowing a yard.

With an ATV boom, I slow down more than I want to, because going too fast leaves stripes.

I learned the hard way that “looks wet” is not the goal.

The goal is even droplets on every leaf, not puddles on the dirt.

Product I actually use: Roundup Custom for Food Plots and a cheap surfactant.

I have used Roundup Custom for Food Plots because it is easy to dose and it is made for this job.

The last jug I bought was about $54 at my local farm store, and it did exactly what it should when I sprayed in good conditions.

I add a basic non-ionic surfactant when the weeds are waxy, because it helps coverage and I do not like gambling on a one-shot spray.

My buddy swears you do not need surfactant if you “mix it hot.”

I have found surfactant plus good timing beats a hot mix on a bad day.

Make the call on water quality, or you will blame the chemical for your water.

Hard water will steal your punch.

If your well water leaves white crust on a bucket, do not pretend it is fine.

Here is what I do.

I use ammonium sulfate in the tank, I mix it first, then I add the herbicide, then I add surfactant last.

I learned the hard way that tossing everything in and shaking like a paint can gives you clumps and uneven spray.

If you are hunting the Missouri Ozarks and hauling water in jugs, forget about “whatever water is around” and focus on clean water from home if you can.

Decide how long to wait before planting, because “brown” is not the same as “dead.”

I like to wait 7 to 14 days after spraying before I plant, unless rain is coming and I need to move.

If I spray and plant the next day, I am asking for weeds to rebound and compete with seedlings.

But if I am planting something like cereal rye as a nurse crop, I will plant sooner because it can handle mess better.

For brassicas and small seed clover, I want the weeds dead, not “thinking about dying.”

If you want my take on what deer do during weather shifts around planting time, this connects to where deer go when it rains because rain changes both spraying windows and deer movement.

Mistake to avoid: Tracking results by feelings instead of checking the plot in 7 days.

I hunt 30 plus days per year, and I still force myself to check plots like a farmer.

Here is what I do after spraying.

I come back in 5 to 7 days, I take pictures from the same corner, and I look for living green centers in the weeds.

If I see survivors, I do not argue with myself.

I hit it again, because the second spray is cheaper than replanting.

FAQ

How long does Roundup need before rain hits?

I plan for 6 hours minimum with no rain, and I sleep better with 12 hours.

I have had “2 hour rainfast” work, but I have also watched it fail on thick weeds.

Can I spray Roundup in the morning if there is dew on the leaves?

I do it if the dew is light and the forecast is dry, but heavy dew can dilute coverage.

If the leaves look like they just got misted with a hose, I wait until they dry a bit and then spray late morning.

How soon can I plant after I spray Roundup on a food plot?

I usually wait 7 to 14 days for a clean kill before planting brassicas or clover.

If I am racing a rain, I will plant sooner, but I expect more weed pressure.

What temperature is too cold to spray Roundup?

If nights are below 40 degrees and the weeds are not growing, I wait.

I have sprayed with daytime highs around 55 degrees and had success if the plants were still active and green.

Why did my weeds turn yellow but not die after spraying?

You probably sprayed stressed weeds, had rain too soon, used hard water, or missed coverage.

I have seen all four happen, and the fix is almost always better timing and a second pass.

Should I spray Roundup or mow first for a better plot?

If you have tall weeds with lots of leaf, spray first, then mow after they brown down.

If you already mowed, wait for regrowth to 6 inches and then spray.

When you are trying to plan plots around actual deer movement, I check do deer move in the wind because wind changes both spray drift and how deer use a plot edge.

If you are new to deer basics and want to talk clearly with your kids or hunting buddy, I still point people to what is a male deer called and what is a female deer called because it keeps camp talk simple.

If you are building a plot near bedding cover, this connects to deer habitat because weeds, edges, and security cover matter as much as groceries.

And if your whole goal is more deer on a budget, I would rather see you read inexpensive way to feed deer than waste cash on gimmicks like I did.

My last pass before I leave the farm.

Here is what I do before I pack up the sprayer and act like the job is finished.

I walk the plot edges and I look for green “islands” I missed, because that is where weeds come roaring back.

I learned the hard way that the edges are where I get lazy.

Back in August 2018 on a little hidey-hole plot in the Missouri Ozarks, I smoked the middle perfect and missed a 6 foot strip on the downwind side.

By October 3 that strip was shoulder-high ragweed, and it stole light from my brassicas like a curtain.

If you are hunting pressured ground like Buffalo County, Wisconsin and your plot is small, forget about “close enough” and focus on those edges, because deer stage there and weeds love it there.

Decide what you are doing about drift, or you are going to smoke something you wanted to keep.

Roundup is not picky.

If it touches your clover, your beans, or the neighbor’s garden, it will try to kill it.

Here is what I do when the wind is sketchy.

I do not spray with a steady wind over 10 mph, and I really like it under 6 mph.

I use bigger droplets and I keep the nozzle low.

I also spray away from the field edge first, then come back and “feather” the edge when the wind lays.

My buddy swears he can spray at 12 mph if he just drives faster.

I have found driving faster just makes stripes and drift, and then you get to buy more chemical and more seed.

This connects to what I wrote about do deer move in the wind because the same wind that makes deer spooky also makes your spray job sloppy.

Mistake to avoid: Spraying and then forgetting you still have to hunt the plot.

I have killed good bucks on ugly plots, and I have watched perfect plots get hunted like garbage.

If your access trail walks right across the food, you are going to educate deer fast.

Here is what I do on my Pike County, Illinois lease where every mature buck has been burned before.

I pick one downwind entry trail, I trim it in July, and I never walk through the middle after August 15.

If I need to check the plot, I glass it from 180 yards with binoculars and I leave.

That is the tradeoff most guys miss.

A plot can feed deer, but it can also turn into a place deer only visit at 2:00 AM if you treat it like a backyard garden.

Product I trust for clean coverage: A Solo backpack sprayer that does not fight me.

I have burned money on gear that did not work before learning what actually matters, and sprayers are on that list.

I wasted $19 on a cheap big-box sprayer that leaked down my leg and lost pressure every 30 pumps.

I switched to a Solo 425 backpack sprayer, and it has been worth it for small plots and touch-ups.

I paid about $129 for mine, and I have replaced one set of seals in six seasons.

Here is what I do with it.

I keep one tip set for herbicide only, and I do not cross-contaminate it with fertilizer or anything else.

Make one simple decision after the kill, or your plot turns into bare dirt.

After Roundup works, you have two choices.

You either cover that dirt with a crop fast, or you invite a brand new weed flush to move in.

Here is what I do if I am not planting for 2 to 3 weeks.

I leave the thatch alone, and I do not “clean it up” with the disc just because I want it to look nice.

Sun on bare dirt is a weed factory.

If you are planting soon, I disturb the soil as little as possible and I plant into dead vegetation whenever I can.

If you want help picking what to plant after you spray, start with what I wrote about best food plot for deer because the crop choice changes how perfect your spray job needs to be.

A real-world check I use: Deer tell me if my timing worked.

I am not a professional guide or outfitter, and I do not pretend I run a farm.

I just hunt a lot and I watch what deer do.

When a plot establishes right after a good spray window, I see daylight use change in about 10 to 14 days.

When it fails, I see deer skirt it and feed somewhere else.

Back in November 2019 in Pike County, Illinois, the morning I killed my 156 inch typical, I watched does filter to a green strip at 7:18 AM after a cold front.

That strip only existed because the weeds were dead and the seed got sunlight.

This connects to what I wrote about deer feeding times because a food plot that actually grows pulls deer into a pattern you can hunt.

One last thing I tell my kids before I let them help spray.

I take two kids hunting now, so I think about simple rules more than I used to.

I tell them Roundup is not magic, and it does not fix a bad plan.

Here is what I do with them on small plots.

I pick one calm morning, I spray steady, and I do not rush just to be done.

Then I come back a week later and show them what died and what lived.

That one check teaches more than any label on a jug.

Wrap-up from a guy who has re-sprayed more than he wants to admit.

If you remember one thing, remember this.

Spray Roundup when weeds are growing, the weather stays dry long enough, and your water and coverage are not working against you.

I have lost deer I should have found and found deer I thought were gone, and I treat food plots the same way.

I try to do the boring parts right so I am not scrambling later.

If you keep your timing tight, you will spend more evenings hunting over green groceries and fewer Saturdays staring at weeds and wishing you had waited one more day.