Alabama Cotton: Gramoxone – A Good Substitute for Glyphosate?

Due to the high price and short supply of glyphosate, many row crop growers are interested in using Gramoxone or generic paraquat products to burndown cover crops and winter weeds before planting. Some have reached out to me for recommendations. We can use paraquat to clean up crop fields and burndown cover crops, but there are a few things growers should keep in mind:

1. Paraquat is not a systemic herbicide; it does not translocate when spray droplets hit plant surfaces. The result is a quick, contact burn that desiccates plant tissues within 2 to 3 days.

Paraquat usually provides a fast kill but does not control regrowth and growing points deep inside the canopy. Therefore, it works better on short vegetation and sporadic weeds. If a field is covered with a thick cover crop and winter weeds that exceed 1 to 2 feet, paraquat is not a good burndown option and significant regrowth should be expected after application.

2. Light intensity is very important for paraquat efficacy. The sunnier the better.

3. Coverage is critical. Use at least 15 gallon per acre water and a surfactant such as crop oil, methylated seed oil and 3 lb/A of AMS to increase efficacy. Higher spray volumes — 20 GPA –may be needed on dense vegetation. Sprayer speeds should be less than 10 MPH for maximum coverage.

4. Coarse droplets offer a balance between surface coverage and canopy penetration. Addition of drift reducing agents may increase canopy penetration and improve control efficacy in thick vegetation.

5. A follow-up application may be required before planting to clean up any regrowth and plants that survived the initial treatment.

6. Tank mixing paraquat with 2,4-D or a PPO herbicide such as Valor, Reviton or Sharpen is feasible to increase broadleaf control efficacy. However, pay attention to mixing sequence as prescribed on product labels to minimize compatibility issues.

7. Clethodim is not a good option to terminate large cereal grain and ryegrass. Tank mixtures with paraquat are required to ensure efficacy. 

Our spring burndown plots were sprayed in mid-late February with AIXR nozzles at 15 GPA. Gramoxone did a good job in terminating cereal rye but was ineffective on crimson clover and tillage radish within the lower canopy. Addition of 2,4-D is required in this case.

Gramoxone-based treatments were less effective on thick ryegrass and large curly dock as compared to Roundup treatments (Note: this ryegrass population is still sensitive to Roundup).

Reviton is a new PPO herbicide which offers comparable burndown efficacy to Valor and Sharpen at a 1 oz/A use rate. It is more active on large cereal rye than Sharpen and Valor, as can be seen from plot pictures. It is mainly used as a burndown herbicide pre-planting on row crop fields with minimum residual activity. Plant back restrictions are 0 days for corn and wheat, 14 days for cotton and soybean.