Project Details:

Title:
Late Herbicide Applications for a Palmer Amaranth: Can We Prevent a Train Wreck?

Parent Project: This is the first year of this project.
Checkoff Organization:Delaware Soybean Board
Categories:Weed control
Organization Project Code:
Project Year:2018
Lead Principal Investigator:Mark VanGessel (University of Delaware)
Co-Principal Investigators:
Kurt Vollmer ((not specified))
Keywords: herbicide, Palmer Amaranth

Contributing Organizations

Funding Institutions

Information and Results

Comprehensive project details are posted online for three-years only, and final reports indefinitely. For more information on this project please contact this state soybean organization.

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Final Project Results

Updated November 6, 2019:
Palmer amaranth control with a single POST application did not provide acceptable control, with 83% control from Enlist Duo being the highest. Liberty plus Enlist One provided only 75% control at 5 weeks after treatment, yet no Palmer amaranth plants were present at harvest. In this trial, Reflex plus glyphosate provided better control than Flexstar GT.

Sequential applications of Engenia plus glyphosate, Enlist Duo, and Liberty provided 97% control or better when rated 4 weeks after treatment. Sequential applications of PPO herbicides Reflex, Cobra, or Flexstar provided similar level of Palmer amaranth control as a single application. Adding Cobra with sequential applications of Engenia, Enlist Duo or Liberty did not improve control; tank mixtures with Enlist Duo resulted in less control than Enlist Duo by itself.

Weed seeds per plant were quite variable and ranged from 4,748 to 38,584. The nontreated plants had the highest number of seeds, yet it was lower than what is often reported. The soybeans were drilled in 7-inch rows presumably increasing soybean competitiveness and helping to limit Palmer amaranth seed production.

There were no yield differences among treatments with the same soybean variety. Herbicide treatments that caused soybean leaf burn (Cobra) did not impact soybean yield, nor did they delay soybean maturity.

Based on preliminary results from one year, sequential applications of dicamba, 2,4-D choline or Liberty are needed to control larger Palmer amaranth plants. Provided Palmer amaranth plants are not taller than 17 inches, excellent control can be achieved with sequential applications of dicamba, 2,4-D choline or Liberty. Sequential applications of PPO herbicides, or including Cobra with sequential applications did not improve control.

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Based on preliminary results from one year, sequential applications of dicamba, 2,4-D choline or Liberty are needed to control larger Palmer amaranth plants. Provided Palmer amaranth plants are not taller than 17 inches, excellent control can be achieved with sequential applications of dicamba, 2,4-D choline or Liberty. Sequential applications of PPO herbicides, or including Cobra with sequential applications did not improve control. Nontreated plants had the highest number of seeds, but narrow row spacing (7") likely contributed to lower overall seed production than reported in the literature due to soybean competition with weeds that limited Palmer amaranth seed production. Future work will examine using cover crop systems to reduce weed emergence and early-season weed growth, in addition to the use of residual herbicides. Such work will provide recommendations on the use of residual herbicides in fields with cover crops.

Project Years