Palmer amaranth has emerged as a top problem weed in the state of Nebraska in recent years — both in terms of higher infestation numbers and resistance to several herbicide chemistries, including glyphosate, atrazine, ALS inhibitors and HPPD inhibitors.
With a declining number of chemical control options, Amit Jhala, Nebraska Extension weed specialist, says integrated approaches are becoming even more important in the fight against Palmer amaranth.
This includes methods such as narrow row spacing in soybeans to limit light interception and soil temperature fluctuation — which weeds like Palmer amaranth need to emerge. However, one practice alone will not be enough to keep weeds in check, Jhala says.
"Without a preemergence herbicide, a 15-inch row spacing alone will not help," he says. "That's why we have to have an integrated approach. Of course, narrow row spacing may help because you will close the canopy earlier, and Palmer amaranth seeds are photosensitive — they need a little light to emerge. In that case, if you nave narrow row spacing, it may reduce the total amount of light that Palmer amaranth seeds are exposed to."
Listen to Jhala discuss other components of an integrated approach — including chemical options and last-resort options for preventing the weed seed bank from growing — in the latest Down in the Weeds.