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U OF ARKANSAS SPECIALISTS: PALMER AMARANTH FOUND RESISTANT TO FIELD RATES OF GLUFOSINATE
Source: blog by Tom Barber, Jason Norsworthy and Tommy Butts, University of Arkansas

To view the complete report, click here.

Last summer an article was written about two fields of concern in Mississippi County where three applications of glufosinate failed to control Palmer amaranth. Upon first observation of these fields, a familiar sinking feeling started to appear.

These left-over pigweed plants were in only a few spots (Figure 1 ) across each field and appeared to be the result of seed from a surviving mother plant the year before. Usually, if resistance is occurring it will be in small spots across the field or in a combined pattern from harvest the year before. These two fields had that "look" and were very suspicious, to say the least.

Figure 1. Palmer amaranth survivors following three applications of glufosinate in Mississippi Co.


Areas of live plants were flagged in each field, and as stated in the earlier post, plants were soaked with 2% solution of Liberty and evaluated ten days later. At time of evaluation, few plants were dead in the area that had been sprayed earlier. Seed was collected from both field sites from matured plants for screening in the greenhouse over the winter in Fayetteville, AR.

Dr. Jason Norsworthy's weed science program at Fayetteville, AR has evaluated both samples from Mississippi County along with another sample collected the previous year from Crittenden County (Figure 2). Initial greenhouse experiments involved a rate response study to evaluate glufosinate effectiveness on these samples.


Figure 2: Palmer amaranth survivors following 5 applications of glufosinate in Crittenden Co.


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