Due to the weather, a number of no-till soybean fields have not received a burndown treatment yet. As a result, many are asking about options for control. First a number of considerations:
2,4-D ester: Rate of 2,4-D may need to be adjusted. Most 2,4-D brands require a 4 week delay between application of 1 qt and planting soybeans. Rates less than 1 qt/A does not provide the same level of horseweed control. The interval between application differs with 2,4-D rates and brands. Be sure to read the label of the brand you intend to use.
Kixor products: These products have good activity on glyphosate and ALS resistant horseweed, but they have a number of restrictions due to crop safety:
|Sharpen Use Rate
|Days Before Planting|
|Coarse Soils Less Than 2% OM||All Other Soils|
|No Other PPA Used||Other PPO (Group 14) Herbicide Used|
Other Group 14 herbicides include all the Authority/Spartan products, Sonic, Valor, Valor XLT, Fierce, Envive, Prefix. Valor has fair activity for control of field pansy (johnny jump up); otherwise most of the PPO herbicides will cause some leaf burn, but they do not improve overall burndown control.
ALS-herbicides/Group 2: These products have been used for dual purpose, help with burndown as well as provide residual control (Canopy, Valor XLT, Envive). A number of fields contain ALS-resistant marestail and these products will not control them. They are fair to good on many winter annuals when used at full rates. So if you want burndown activity from these products, be sure to use the full rates.
Glyphosate: Since most weeds are larger then we typically treat them, consider increasing rates to compensate for the larger size.
Liberty or Gramoxone: Some may be tempted to use Liberty or Gramoxone in place of glyphosate, keep in mind that this year weeds are larger than usual at burndown and these products are less effective on larger plants. Furthermore, both perform much better when applied during full sunshine and require good spray coverage (i.e. 20 gallons per acre of spray volume). Including metribuzin with either Liberty or Gramoxone improve overall burndown activity.
Burndown weed control for no-till soybeans will be challenging this year due to the prevalence of horseweed resistant to both glyphosate and ALS herbicides, and the size of many of the winter annuals. Evaluate the winter annuals present, as well as consideration of the summer annual weeds anticipated, and develop herbicide programs on a field by field basis. In fields with history of difficult burndown weed control it may be best to use the higher rate of 2,4-D and apply the residual herbicides at planting (two passes) which may delay planting, but provide highest level of weed control.
The use of residual herbicides for soybeans is something many are aware of and are looking at using for fields with Palmer amaranth and morningglory. Remember, the residual herbicide needs to be effective on the targeted species. An ineffective herbicide or low rates probably will not provide the activity you anticipate or need.