3 min read
redroot pigweed

Cotton commodity prices have plummeted over the last weeks and are now at or well below the cost of production. Looking for ways to survive, some growers are thinking about a “dirt cheap” way to manage this crop.

In such situations, chemicals and fertilizers are typically among the first inputs to reduce. But overly reducing weed control efforts could seriously affect future operations. Weeds are persistent problems and cannot walk or fly away from a field or farm. One year of sloppy pigweed management can result in significant expenses for cleanup over the next 3 to 5 years.

The following are recommendations for maintaining sufficient weed control but not at a high cost.

Burndown

  • Marestail fields: Roundup + Sharpen 1 ounce/acre.
  • No-till or conventional till cotton fields: Roundup + Valor 2 ounces.
  • If generic glyphosate is used: add NIS surfactant at 0.5 gallons per 100 gallons of spray solution.

PRE (From 3 Days before Planting to 3 Days after Planting)

  • Pigweed and grassy fields: Warrant 3 pints/acre.
  • Fields general broadleaf weeds such as pigweed, sicklepod, morning glory, teaweed, etc.: Cotoran 2 pints/acre.
  • Heavy pigweed and grass pressure: Reflex 8 ounces + Warrant 2-2.5 pints/acre is a great choice.
  • For PRE herbicide activation, a 0.5-inch rainfall is needed for activation. If soil moisture is very good at herbicide application, 0.25-0.5 inch rainfall may can activate these herbicides too.
  • Add 1.5-2 pints of Gramoxone if weeds have emerged at planting.

For Fields with Pigweed

  • First POST over the top of cotton (at 20 to 25 days after planting): Roundup PM 32 ounces + Xtendimax/Engenia (Xtend Cotton) or Enlist One (for Enlist Cotton only) + Warrant 2.5 pints or Dual Magnum 16 ounces or Outlook 13 ounces (or a generic version of these Group 15 herbicides). Timing is absolutely critical. Treatments need be made when weeds are less than 3 to 4 inches tall. As soon as pigweed can be seen on the ground, get sprayer ready and spray them.

Follow-up Post or Layby

  • If first POST applications for pigweed were made in a timely manner and if residual herbicides from Group 15 (Warrant, Dual, Outlook, or generics of these herbicides) have been activated by rainfall, apply Valor 3 ounces or Cotoran 2 pints/acre about 2-3 weeks later using a layby, hooded, or post-direct sprayer. Cotton needs to be at least 10 to 12 inches tall to minimize crop damage. Use a coarse droplet nozzle if possible. If some pigweed survived first POST, spot spray Liberty or a generic glufosinate and follow with the layby, hooded, or post-directed treatment. Add MSMA in layby or directed spray will enhance grass and nutsedge control.
  • Two generic glufosinate (Liberty) products, Scout from Valent and Interline from UPL, performed equal to Liberty in AL trials last year. Liquid AMS has shown promise in enhancing the control of large sicklepod and pigweed with glufosinate.
  • The game plan is simple. Try to start clean, spray everything timely, and use plenty of cheap residual herbicides in PRE, first POST, and layby applications, hopefully to avoid a second broadcast treatment over the top using more expensive POST herbicides. If the rain continues and growing conditions remain mostly normal, producers should get through in-season weed management at about $30 per acre with discount programs from manufactures and using cheaper generics.
  • Don’t forget to cut off pigweed seed heads before picking cotton. Pigweed produces many seeds per female plant and should not be ignored.

For Fields without Pigweed

  • First POST over the top (at 20 to 25 days after planting): Roundup PM 32 ounces + Warrant 2.5 pints/Dual Magnum 16 ounces/Outlook 13 ounces/or a generic of these Group 15 herbicides. Add liquid AMS to enhance control of large broadleaf weeds and nutsedge. Use 2 ounces of Staple LX with Roundup instead of Group 15 herbicides if morning glory and nutsedge have been problematic in the past. After another 2 to 3 weeks, if fields remain mostly clean and cotton is more than 12 inches tall, apply Valor 3 ounces or Cotoran 2 pints/acre in a hooded, post-direct, or layby sprayer. Add MSMA in layby application to provide grass and nutsedge control. If some weeds survived first POST, spray Roundup again to finish them off. Add a NIS to generic glyphosate to enhance efficacy. Spot spray pigweed or morning glory with Liberty. Then follow with the hooded, post-directed, or layby application.

 

Featured image by Phil Westra, Colorado State University, Bugwood.org

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