With the discovery of glyphosate-tolerant pigweed in northeast Arkansas what are some treatment recommendations? Bob Scott and Ken Smith, Arkansas Extension weed scientists, offer the following:
• Begin clean by utilizing a good burndown program of either glyphosate or Gramoxone plus Valor at recommended rates. Tillage can also be utilized instead of chemical control and is good resistance management.
• Where tillage is used to start clean, begin with a true pre-emergence application of either Valor of Dual Magnum. Whether used in a burndown or pre-emergence application, under favorable conditions, the two products should provide three to four weeks of residual control of pigweed.
• Flexstar at 1.25 pints per acre in-crop will provide good control of Palmer amaranth that is below 2 inches tall. This can be tank-mixed with glyphosate for effective control of other weeds present.
• Prior to pigweed emergence, Sequence herbicide (glyphosate plus Dual), or a similar tank-mix can be used early post to extend the residual control of pigweed.
• Crop rotation to rice is a good resistance management strategy. However, care should be taken to control pigweeds around field edges and levees.
• If you suspect a field has resistant pigweed always clean equipment prior to moving from that field to another area.
• A yellow herbicide such as Treflan or Prowl applied ppi will prevent many pigweeds from becoming established early season.
• Applying Cotoran, Caparol or Direx pre will also delay the emergence of pigweed.
• Metolachlor products such as Dual Magnum applied with glyphosate before cotton reaches fifth leaf will control pigweed until the crop is large enough to make post-directed herbicide applications.
• Post-directed and lay-by applications that include a herbicide with residual properties will keep pigweeds under control until the canopy creates sufficient shade to control pigweed seedlings. Herbicides such as Caparol and Direx in post-directed programs — or Valor at lay-by — have been extremely effective in keeping pigweed under control.