Learn About Equipment and Pesticides

This question can only be answered if you know the calibration rate – how many gallons per acre (GPA) your sprayer is applying. Several factors influence the calibration rate of your sprayer, including pressure, speed, sprayer type, and YOU the applicator. Even when using a gallon-sized hand sprayer, it should be calibrated or else you risk significantly over- or under-applying the herbicide.

To calibrate your sprayer, see How do I calibrate my sprayer below.

If your sprayer is already calibrated, here is an example calculation to determine the amount of herbicide to put in your sprayer:

  • The label of Product A recommends that you apply one quart (32 oz) of herbicide per acre. Your 2-gallon hand sprayer has a calibration rate of 40 gallons per acre.
    • (32 oz herbicide / 1 acre) * (1 acre / 40 gal) = 0.8 oz herbicide per gallon of water
    • (0.8 oz herbicide / 1 gal water) * 2 gal / tank = 1.6 ounces herbicide / tank
      • You would need 1.6 ounces in this 2-gallon sprayer
    • Remember, applying more than the recommended rate may have negative impacts and is in violation of the label.
    • Want more examples? Try a few practice problems here and check your answers!

The best calibration method depends on the type of sprayer you are using.

Equipment should be calibrated at least once per season under conditions that are similar application conditions (i.e. a bumpy field vs. a paved parking lot).

Rinse and flush equipment after use.
Dispose of rinse water away from water supplies.
Rinse a second time adding household ammonia- 2oz/gallon of water.
Circulate through equipment and let stand for several hours.
Flush the solution out of the handgun or boom.
Rinse the system and circulate twice more with water.
All containers must be triple rinsed and recycled. The triple rinse procedure is as follows:
Empty the remaining contents into your application equipment and allow to drain for 10 seconds.
Fill container ¼ full with water and shake with lid tightly secured for 10 seconds.
Empty and drain into equipment.
Repeat two additional times.
Make sure to puncture the container so that is cannot be mistakenly used for anything else.
The Wyoming Weed and Pest Council promotes Integrated Pest Management (IPM). This approach uses multiple control techniques with the specific goals of; decreasing costs, increasing control, creating synergistic effects, monitoring success, and continued effort.

IPM methods include-

  • Cultural control – modifying behaviors to prevent noxious weeds from being introduced and includes; education, prevention, early detection of new invasions, modifying grazing habits, replanting disturbed or previously infested areas with native species, and monitoring successes and failures.
  • Physical control – this is the use of physical or mechanical methods to control weed infestations. Physical control can be; mowing, chopping, pulling, cutting, burning, and tilling. Remember to identify what weeds are to be controlled, as some physical control methods can aggravate root spreading perennial weeds! Mechanical Control Video
  • Biological control – this is the use of introduced competition or predation. Often introduced noxious weeds are problems because they have been removed from their natural enemies. Biological control includes introducing insects, predators, and pathogens to control weeds as well as correctly timed grazing by species that will eat the weeds.
  • Chemical control – is the use of herbicides to control weeds. This is often the most effective control technique and if used correctly can safely and greatly reduce infestations.

In summary a good IPM plan will be a mix of all of these techniques, please consult your local Weed & Pest District for help in creating your comprehensive control plan as these may vary depending on property size, weeds present, and extent of infestation.

When considering your options for difficult to control weed species, the selection of an appropriate surfactant or adjuvant can be nearly as important as choosing the appropriate herbicide. Adjuvants and surfactants are additives to your spray solution that make your control efforts more effective. The most common surfactant is a non-ionic surfactant. These surfactants work by helping to break the water tension of your spray droplets allowing each droplet to better spread out across the leaf surface – increasing the potential for the herbicide to do its job. In a bind, you can try using a couple of drops of dish soap to create a similar effect but, soap is ionized and can potentially impact your herbicide’s effectiveness. See why here.

For plants that have a thick waxy cuticle like Dalmatian toadflax or for plants with a hairy leaf like houndstounge – a more complex surfactant might improve your results. Many Districts have started using a three way blended surfactant that includes; a non-ionic surfactant, methylated seed oil, and a wetting agent. These surfactant blends allow the herbicide to stay on the plant with better coverage while helping to successfully penetrate the cuticle.

So the next time, you’re not seeing the results you expected instead of adding more active ingredient – consider trying a surfactant to improve your results; it’s probably cheaper and it’s likely better for the environment.

Please follow the directions on the label or consult your local Weed & Pest District.
All of the Weed and Pest Districts make a concerted effort to use the best management practices available and the safest pesticides for staff, residents and the environment. For details on specific products please consult your local Weed & Pest District. To learn more about pesticide safety in general, check out the National Pesticide Information Center.
The Wyoming Department of Agriculture website contains all the information you will need in order to learn about completing your applicator exam. Please visit their website at: WY Dept. of Agriculture- Pesticide Applicator Training