Overreliance on a single weed-control method causes resistant weeds to develop and puts the herbicide-tolerant system used and the ability to grow a crop in a specific field in jeopardy. When resistant weeds develop, farmers face the additional costs required to control them—unplanned herbicide applications, intense manual labor, and in extreme cases, total crop loss. Integrated Weed Management practices help to preempt these issues and result in successful management of resistant weed populations.
Integrated Weed Management techniques are effective in reducing problems with herbicide tolerant and or herbicide-resistant weed biotypes. It is best to use multiple practices to manage or delay resistance, as no single strategy will be completely effective on its own.
1 Know Your Weeds. Know Your Fields.
Proper identification of weed species will help pinpoint which herbicide program will work best on every acre. It is equally important to understand the weed pressure and history within each field. Closely monitor problematic areas with difficult-to-control weeds or dense weed populations. Scout for weed escapes and look for the following indicators to identify resistant weeds.
Indications of Potential Weed Resistance:
- A patch of weeds occurs in the same area year after year and is spreading.
- Dead weeds appear next to surviving weeds after the same herbicide application.
- Many weed species are managed, but one particular weed species is no longer controlled. For example, following a glyphosate application, actively growing marestail can still be seen in the absence of other weeds.
- The field has been sprayed repeatedly with the same herbicide mode of action, particularly if there was no mode-of-action diversity in the weed management system.
2 Start Clean
Effective tillage or the use of a burndown herbicide program can control emerged weeds prior to planting. Regardless of the tillage system, a pre-emergence or early postemergence soil-applied residual herbicide should be a part of every weed control program.
3 Stay Clean - Use Overlapping Residuals
In any weed management program the goal should be to control at least 80 percent of the weed population with residual herbicides. Residual herbicides applied at burndown, planting or tankmixed in the first post application with Liberty® herbicide help ensure optimal weed management, particularly if environmental conditions delay timely post applications.
Under intense weed pressure, use overlapping residual herbicides to minimize weed competition for soil moisture, light and nutrients. Maintain soil residual herbicide activity with overlapping soil residual herbicide applications from burndown through canopy closure. This reduces weed selection pressure and helps avoid weed escapes.
4 Apply Herbicides Correctly
Ensuring proper herbicide application maximizes weed control and minimizes potential for weed escapes.
- Apply to actively growing weeds - Herbicides provide peak performance when applied to small, actively growing weeds. These weeds absorb more of the active ingredient, particularly with adequate soil moisture, sunlight and optimal soil nutrients.
- Apply when weeds are no more than 3 to 4 inches - Apply postemergence herbicides soon after crop emergence when weeds are no more than 3 to 4 inches tall. This is typically 10 to 14 days after crop emergence. The use of pre-emergence residual herbicides provides critical control of early season weeds that result in the greatest crop yield reduction. Plus, residual herbicides help ensure optimal weed management, particularly if environmental conditions delay timely post applications.
- Follow label instructions - Read and follow all label instructions to ensure proper application. Factors affecting weed control include spray coverage, carrier volume, application speed, adjuvants and tankmix partners. When you apply a herbicide at a rate less than listed on the label, the result can be insufficient control and will have a significant impact on the immediate weed control and resistance risk.
5 Do Not Allow Weed Escapes
Treat every weed escape as if it is a resistant weed. Problematic weeds that escape herbicide applications should be controlled to reduce weed seed production. Consider spot herbicide applications, row wicking, cultivation, hand removal of weeds and other techniques to stop seed production and improve weed management for the subsequent growing seasons.
6 Zero Tolerance - Reduce the Seed Bank
Do not allow surviving weeds to set seed in order to decrease weed population shifts from year to year and prevent major weed shifts. One Palmer amaranth plant can produce up to 1 million seeds per plant in optimal conditions. The weed seed bank grows by allowing partially controlled weeds to reproduce and set seed. The larger the pool of weed seed in the soil seed bank, the greater the probability that weed resistance will arise.
7 Clean Equipment
Avoid moving equipment that has not been thoroughly cleaned. This will help prevent the spread of herbicide-resistant weeds and their seeds and reduce the potential of introducing new invasive weeds onto other acres.