Pigweeds & Better Weed Management | Great Days Outdoors

Fighting the battle against unwanted plants

Pigweed (Palmer Amaranth) has been a frequent topic of conversation among farmers and food plot guys in the last several years.

Pigweed has been causing severe problems because of its rapid growth and in many parts of the county, resistance to glyphosate, which leads to problems in glyphosate resistant crops that are being grown.

In warm season food plots, whether it is a spring planted perennial or annual blend, pigweed can very quickly become a problem and overtake the plot. When left to mature and go to seed, pigweed grows a substantial amount of seeds that can continue to cause problems for years down the road.

They key to killing and controlling pigweed is early identification and proper herbicide application. Imazamox is a great broadleaf control herbicide with chemistry that has excellent results and residual control on pigweed and other broadleaf weeds.

Imazamox (brand names Weed Reaper or Raptor) can be sprayed over legumes including clover, alfalfa, beans, peas and lablab. Ideally, broadleaf weeds should be less than six inches high for the best kill.


My first experience in testing imazamox was on a severe infestation of pigweed on more than 10 acres of spring planted lablab a few years ago. The lablab was less than two weeks out of the ground when I noticed a solid carpet of pigweed beginning to emerge. Left untreated, the lablab would have easily been outgrown by the rapid growth of pigweed and my summer crops would have been non-existent.


This clover and chicory kept clean with selective herbicides will stay healthy for most of the year. Photo by Austin Delano


95 Percent Kill Rate

I tested Weed Reaper Broadleaf Control (active ingredient imazamox) at a rate of four ounces per acre with AMS (ammonium sulfate) and a surfactant as a tank additive. I was pleasantly surprised on my return trip to the fields to find a better than 95 percent kill on all broadleaf weeds including the solid carpet of pigweed that was completely nuked.

The only areas I could find with less than ideal results were due to inconsistent spots in the spray pattern and not failure on the herbicide. These were all at the end of my turn rows where I didn’t get quite enough overlap.


“The use of herbicides is one of the greatest tools a wildlife manager can utilize to keep weeds under control and get the most out of your plantings. Here are a few tips to get the most from your efforts.”

If you have trouble growing warm season plots because of broadleaf weeds, imazamox may be your answer. Nobody likes to spend the money and effort of planting only to have it ruined by problematic weeds.

One of the most common problems in food plots, especially perennials, is weed competition. Weeds rob your plot of essential nutrients, water and root space. Given time and opportunity, weeds will quickly mature, produce seed and overtake a well-intended food plot. The use of herbicides is one of the greatest tools a wildlife manager can utilize to keep weeds under control and get the most out of your plantings.

Tips For Better Management

Here are a few tips to get the most from your efforts.

  • Read the label. The information on the herbicide labels contain great info and will identify what weeds they control and what crops the product is designed to protect.
  • Spray when grasses or broadleaf weeds are young and thriving. If you wait to spray when they are tall and mature, the results will often be less than desirable. If weeds are already tall and maturing, mow first and return seven to 10 days later to spray the new re-growth.
  • Spray in good conditions. Cloudy and still days are best. Windy and rainy days do not allow good conditions for spraying.
  • Make sure spraying equipment is functioning properly and carry some spare spray rig parts to the field. There’s nothing worse than having a busted hose or clogged tip in the field and be without the tools to fix it.
  • Make sure to add a surfactant or crop oil when needed. Many grass-specific herbicides do not work well without one.
  • For optimal results, use AMS in your tank mix when spraying selective herbicides. AMS will increase the effectiveness of the herbicide by helping the weeds readily trans-locate it to the roots for a good kill.
  • Know the size of the fields you are going to be spraying so you can apply the appropriate amount of solution. To practice and calibrate your sprayer, find a field and measure it with a GPS or use a rangefinder to determine the acreage. Fill your spray tank with just water and take note of the speed you travel and the amount of water you apply over the known area. This will help take out a lot of guesswork on applying the correct amount. Most herbicides work best when 12 to 20 gallons of water are used over an acre with the appropriate herbicide.


Make sure to always read labels with any herbicide application. Photo by Austin Delano


Sprouting Up

Another very common problem is the flush of weeds you get after planting warm season annuals such as soybeans, peas or lablab. Anytime you disturb the ground with a piece of equipment like a disc, harrow or tiller you are likely to get a fine crop of weeds that germinate from seeds that have been in your soil profile for years waiting on their chance to grow.

Frequently, these weeds will outgrow the crop you have planted and end up choking it out. I typically use this sequence in the spring when planting my warm season annuals. Keep in mind that glyphosate (Roundup) is a contact and non-residual herbicide. If it doesn’t contact something green and growing, it is basically inactive. It does not have any residual activity in the soil and will not affect seeds you are preparing to plant.

I generally spray the area to be planted after a good portion or the entire plot has a good flush of spring weeds. In the South, this is usually around early to mid-April. Wait about a week. Then, go in and work the soil with a disc or tiller or whatever your primary tillage equipment is.

This disturbance of the soil should create a new flush of weeds over the plot in a relatively short period of time. After I see a good carpet of weeds starting to emerge, I spray again with 41 percent glyphosate (generic Roundup).

Wait just three to five days and lightly prepare the top two to four inches of soil again and plant. This second spray application seems to really cut down on early weed problems in spring planted plots. Giving the plot you are planting time to get established and canopy out to shade the soil will drastically cut down on the amount of weeds that can grow.

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