Things you can do NOW to have fewer weed issues LATER

It is difficult to believe that with Labor Day weekend fast approaching summer and the 2025 growing season are winding down. In my travels in northwest Minnesota during the wheat and sugarbeet pre-pile harvest, I have captured a couple of pictures of ‘low-hanging fruit’-type actions that one could take that would assist you in your battle with weeds in years to come. These include managing weeds on field edges, harvesting around (not through) weedy patches, taking notes about weed management successes and failures in 2025 and rogueing weeds.

Edge of field weed management

Consider pulling out the mower and spending some quality time in the mild temperatures, fresh air and sunshine to mow down all of the tall weeds growing up along the outside edges of your production fields (Figure 1). Mowing and blowing the chaff in the opposite direction of your production field ensures that weed seeds are deposited outside of your field. Mowing may also help to destroy a significant proportion of viable weed seeds. Lastly, once weed seeds are in contact with the soil or other plant material, they are more likely to be consumed by insects and other small animals and microbes looking for a meal.

Figure 1. Mowing weeds on field edges and blowing chaff away from the production area can decrease weed seed viability, increase the chances that seeds are eaten by animals and reduce the potential that seeds add to the field’s weed seed bank. Photo: Angie Peltier

Combines are GREAT weed seed spreaders

Sending weeds with viable seeds through a combine during harvest is demoralizing, particularly after spending so much time and money on weed management during the growing season. What might not immediately come to mind, however, is that combines are really great at spreading weed seeds away from their point of origin in the direction of harvest, thereby making the field area in need of intensive weed management next year larger than the area impacted by weeds in 2025.

While it may seem like leaving money on the table by leaving yield in the field, in this low-commodity-crop/high-input-price environment, it might be an economical yield loss to harvest AROUND rather than through weedy patches when one thinks of the difficulty of battling troublesome weeds into the long-term over a larger area (Figure 2).  

Figure 2. Notice this weedy patch left standing in an otherwise-harvested spring wheat field near Crookston, MN. Leaving weeds standing in place rather than running them (and their seeds) through a combine can reduce the field area in need of intensive weed management in future years. Photo: Angie Peltier

Take notes of weed management successes and failures

As you check your crops for maturity and moisture in preparation for harvest, be sure and have your smart phone, notebook or other notes capturing tool handy to take notes of your weed management successes and failures in 2025. If one weed management burndown, pre- and post-emergence regimen worked well in your spring wheat crop in 2025, plan to reserve this regimen for the next time you grow spring wheat, planning to use herbicides from different herbicide groups in 2026.

Active ingredients from the same herbicide group act similarly in a plant and so if, for example, your field’s waterhemp population is resistant to the herbicide Flexstar (herbicide group 14), your field’s waterhemp population will also be resistant to Cobra (also in herbicide group 14). Rotating among herbicide groups and tank mixing herbicides from more than one herbicide group are strategies to slow the speed that weed populations evolve to overcome genetic herbicide resistance. Tank mixing herbicides from different groups means that if a weed plant is resistant to one of the herbicide groups but not the other, the application would still be able to manage that weed as there is less of a likelihood of a single weed plant simultaneously evolving resistance to more than one herbicide group. If a management strategy that you used in 2025 didn’t work so well, consider working with your co-op, agronomist or University of Minnesota Extension to devise an alternative strategy for 2026.

Pulling weeds is time well spent

If you are anything like I am, besides soil sampling, there is very little else about raising crops that I like less than pulling weeds. However, we know way too much about herbicide resistance to NOT pull weeds.

There are two primary ways that a herbicide resistant weed seed develops: random mutations and gene shuffling during sexual reproduction. Whenever cells replicate, the genetic material called deoxyribonucleic acid (DNA) also replicates. Sometimes simply due to random chance, mistakes are made during the DNA replication process. While a proofreading mechanism exists in cell nuclei to fix these mistakes, sometimes these mistakes aren’t corrected. Should a mutation occur in a gene that when expressed allows a weed plant to better survive a herbicide application, the weed plant with this mutation is able to reproduce to set seed after an application, while those without this mutation cannot.  

To visualize how genetic recombination (gene shuffling) works, we only need to think about one of the toughest weed menaces in Minnesota – waterhemp. Waterhemp has male and female plants and has to outcross (pollen from the male plant fertilizes ovaries from the female plants) in order to produce seed. During sexual reproduction, chromosomes (concentrated DNA molecules from each parent) from the female parent line up next to the same chromosomes from the male parent. While each parent has similar genes arranged across the length of a given chromosome, they may have different versions, or alleles of the same genes. For example, both parents have a gene for seed coat color, but one may have an allele that when expressed produces pale seed coats, while the other parent has an allele that when expressed produces dark colored seed coats. When the genes align during reproduction, portions of the seed coat color gene can break and move from the male-supplied chromosome to the female-supplied chromosome and vice versa resulting in alleles for seed coat color different from either parent.

Gene shuffling and/or randomly occurring mutations that occur in a portion of the genome that allows a plant to survive a herbicide application to reproduce and set seed results in a herbicide tolerant weed population. This process all begins in a single seed. This means that if one observes a single surviving plant in a field that had been sprayed with a herbicide, there is a possibility that the plant is herbicide tolerant (Figure 3). Be sure that you bring along a large contractor's bag or other sturdy, leak-proof bag that you can use to carry weeds out of the field for later burning, composting or burying. Leaving weeds in the field after pulling them also leaves weed seed in the field. Rogueing or hand-pulling that plant can be the difference between taking out a single, herbicide-resistant weed plant in 2025 and battling a herbicide tolerant weed population for years to come.

Figure 3. Hand pulling weeds that survived your 2025 management is time well-spent as you may in fact be pulling out a herbicide resistant plant. Bag the plant and carry it out of the field to burn, bury or compost it and keep it from dropping viable seeds in the field. Photo: Angie Peltier