Decisions are easily put off until we absolutely must make a choice. To some degree prolonged decision making has caused us to lose ground in the prevention of herbicide resistant weeds. For many, reliance on glyphosate has been very convenient for delaying crop selection for a particular field until about the time the planter rolled into it. However, reliance on this single chemistry has put extremely high selection pressure on weed species like Palmer amaranth. After many years of applications under a single chemistry application significant weed populations of resistant weeds have developed. Currently in the United States, there are 145 or so weeds that have been identified as resistant to herbicides. Globally 404 unique cases of herbicide resistant weeds have been observed.
Growers can do several things to reduce or prevent the development of herbicide resistant weeds. The first is applying residual herbicides with multiple modes of action. Unfortunately, that may force a grower into locking in a decision as to what will be planted on a given location, but it is an important first step in managing weed resistance. During individual herbicide applications, multiple modes of action can be utilized with premix or tank-mixed herbicides. Rotating from one crop to another will also typically allow for rotation to herbicides with different modes of action for a particular field. Ensuring that we plant into weed free fields is essential; be that done with herbicide or cultivation. Although cultivation is often important to successful crop establishment, this mechanical form of weed control can also aid in efforts to prevent resistance. Scouting fields and surrounding boarders/turn-rows for weeds can help in weed management efforts. Catching young actively growing weeds will improve whatever control option is selected and prevent a new distribution of weed seed.
As always, the herbicide label is the law. Not only should we always follow the label in regards to application rates, but we should also follow suggested amounts of carrier to apply herbicides and include any recommended adjuvants.
Reliance on a single mode of action herbicide may very well be a low cost flexible weed management option today, but continued reliance on this type of system will guarantee that your neighbor’s problem or the problem of a grower a few counties away will soon be your problem. Palmer amaranth produces up to one million seeds per plant. With those kinds of numbers it doesn’t take long for a single resistant plant to cover a field with other resistant weeds. Therefore as we move closer to planting, growers should begin making crop selection decisions and applying appropriate pre-emergent herbicides.
Individuals with disabilities, who require an auxiliary aid, service or accommodation in order to participate in any of the mentioned activities, are encouraged to contact the County Extension Office eight days before all programs for assistance. Extension programs serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability or national origin.