Cultural Weed Control Practices

Mark VanGessel, Extension Weed Specialist;

A number of questions this spring have started with “what’s the cheapest herbicide program to control …”. Lots of folks are looking to cut input costs and expenses and herbicides are an obvious target. Keep a few things in mind.

  1. Respraying to control weeds that escaped the first application is not cheap
  2. If you do not have herbicide-resistant weeds, you do not want to get them. Herbicide-resistant ragweed and Palmer amaranth are not cheap or easy to control and once you allow them to go to seed, they will be there for years to come.
  3. In many situations WHEN a herbicide is applied can be as (or more) important than WHAT herbicides are applied. A really good herbicide applied too early before planting or to weeds that are too large or not actively growing can result in poor control
  4. Know your problem fields and be realistic about your workload. Do you own a sprayer? Can you get to the problem fields in a timely fashion? Are the problem fields close to your base of operation? If you answer yes to all, you have more flexibility in your herbicide selection. If you have problem fields, but they are not in close proximity to your main operation, then you need to think about using a program that provides longer residual control or more effective on larger plants, and often times this means a more expensive program.
  5. Crop management is critical for full-season weed management. A vigorously growing crop that develops an early crop canopy that shades the ground is one of the best tools. Using a well-adapted variety or hybrid, planted at the right time, with a good fertility program is vital.
  6. Row spacing is very important for soybeans and sorghum; planting in 15-inch rows dramatically improves full-season control compared to 30-inch rows. This is due to how quickly these crops form a dense soybean canopy to shade shorter weeds. Other crops planted in narrow rows such as corn have not shown the same benefit for weed suppression.

Use an effective herbicide program. Most situations require more than a single herbicide application, so consider all herbicide applications when developing your program. If you are planning on a two-pass program and you are likely to get your herbicide applied in a timely fashion, you probably will not need the high price program to achieve excellent control if you can replace cost with timely management.