Palmer amaranth recommendations for 2014 growing season
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 increased weed infestations, said a University of Illinois weed sciences researcher.
“If ignored or otherwise not effectively managed, Palmer amaranth can reduce corn and soybean yield to nearly zero,” said Aaron Hager. “The threat of Palmer amaranth during the 2014 growing season is very real across a large portion of Illinois.”
The U of I weed science program has developed recommendations for management of Palmer amaranth in agronomic crops. These recommendations were developed in accordance with the unique growth characteristics of this weed species. The goals of the recommendations are twofold: to reduce the potential for Palmer amaranth to negatively impact crop yield, and to reduce Palmer amaranth seed production, which ultimately augments the soil seed bank and perpetuates the species.
Three general principles of Palmer amaranth management include:
- Prevention is preferable to eradication. Prevention refers to utilizing tactics that prevent weed seed introduction and weed seed production. “Palmer amaranth is not native to Illinois so any population discovered in the state originated from seed that somehow was moved into the state,” Hager said. “The myriad of ways in which Palmer amaranth seeds can be transported, however, 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.”
- 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.
- Control of Palmer amaranth should not be less than 100 percent. “In other words, the threshold for this invasive and extremely competitive species is zero,” the researcher said. “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.”
Recommendations based on Palmer amaranth germination and emergence characteristics include:
- Be certain to control all emerged Palmer amaranth plants before planting corn or soybean. Burn-down herbicides or thorough tillage are effective tactics to control emerged Palmer amaranth plants before planting. Keep in mind, however, that glyphosate will not control glyphosate-resistant Palmer amaranth and that growth regulator herbicides (such as 2,4-D or dicamba) are most effective on Palmer amaranth plants less than 4 inches tall. If pre-plant scouting (which is especially important prior to planting soybean) reveals Palmer amaranth plants taller than 4 inches, consider using tillage instead of herbicides to control the plants.
- Apply a full rate (based on label recommendations for soil texture and organic matter content) of an effective soil residual herbicide no sooner than seven days prior to planting and no more than three days after planting. Many soil residual herbicides that are effective for controlling waterhemp are also effective for controlling Palmer amaranth. In soybeans, products containing sulfentrazone (Authority) or flumioxazin (Valor) have provided effective control of Palmer amaranth. Application rates of products containing these active ingredients should provide a minimum of 0.25 lb ai/acre sulfentrazone or 0.063–0.095 lb ai/acre flumioxazin.
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