Palmer amaranth is a weed species that must be thoughtfully and carefully managed; simply attempting to control Palmer amaranth often leads to ineffective herbicide applications, substantial crop yield loss and increasing weed infestations. Ignored or otherwise not effectively managed, Palmer amaranth can reduce corn and soybean yield to near zero. The threat of Palmer amaranth during the 2014 growing season is very real across a large portion of Illinois.
These weed management recommendations were developed in accordance with the somewhat unique growth characteristics of Palmer amaranth. The goals of the recommendations are to reduce the potential for Palmer amaranth to negatively impact crop yield, and to reduce Palmer amaranth seed production that ultimately augments the soil seed bank and perpetuates the species.
1. Prevention is preferable to eradication. Prevention refers to using tactics that prevent weed seed introduction and weed seed production. The myriad ways in which Palmer amaranth seeds can be transported, makes preventing seed introduction extremely challenging. Once Palmer amaranth populations become established, utilizing any and all tactics to prevent seed production becomes of paramount importance.
2. It is not uncommon for annual herbicide costs to at least double once Palmer amaranth becomes established. There are simply no soil- or foliar-applied herbicides that will provide sufficient control of Palmer amaranth throughout the entire growing season. At least three to five herbicide applications per growing season are common in areas where Palmer amaranth is well established.
3. Control of Palmer amaranth should not be less than 100%. In other words, the threshold for this invasive and extremely competitive species is zero. Female Palmer amaranth plants produce tremendous amounts of seed and in less than five years a few surviving plants can produce enough seed to completely shift the weed spectrum in any particular field.
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