Q: What is your recommendation for someone who wants to plant wheat, but has a lot of winter annuals coming up, including marestail? I’d like to no-till the wheat and use a burndown, but am concerned about using 2,4-D right before planting. Can it damage the wheat seed and hurt germination?
A: Nebraska Extension Weeds Specialist Amit Jhala: The 2,4-D label for fall application is a little complicated for use as a burndown before planting wheat. For example, the label of 2,4-D LV4 is a little vague about the required waiting time between application on fallow or stubble ground and wheat planting.
When used on fallow ground or crop stubble, the label states you can plant only those crops listed on the label within 29 days after application of 2,4-D LV4. Wheat is one of the crops listed on the label, so that’s fine; however, the label also states that wheat and other crops listed on the label may be at risk of crop injury or loss if planted soon after application, especially during the first 14 days.
The risk of injury to wheat following a 2,4-D application to fallow or crop stubble increases:
- at higher use rates,
- if soil temperatures have been cold, or
- if soils are excessively wet or dry in the days following application.
All of these factors affect the degradation of 2,4-D LV4 after application. The greatest risk of crop injury to wheat would occur with 2,4-D application close to planting and a good rainfall shortly after planting.
In practice, the risk of injury is probably minimal if you allow a seven-day waiting interval between application of up to 1 pint/acre of 2,4-D LV4 and planting wheat.
- Glyphosate can be tank-mixed with 2.4-D to improve efficacy.
- Sharpen should provide good burndown activity, but limited residual control of marestail that emerge after application. The rate can be increased from 1 to 2 oz/acre to improve the length of residual.
- Elevore (halauxifen-methyl) can be applied at a rate of 1 fl oz/acre for marestail control; however, it requires a 14-day interval before planting wheat.
- Gramoxone should also effectively control small seedlings of marestail and other winter annuals.
- Aim (carfentrazone) and Amber (triasulfuron) have no planting restriction and can be applied anytime as a burndown or after wheat has emerged.
- Harmony SG (Thifensulfuron) and Express (Tribenuron) can also be used anytime, except during the period of wheat emergence through the one-leaf stage; however, remember that several marestail populations are resistant to ALS-inhibiting herbicides. If your marestail does not respond to these two herbicides, it is more likely resistant to an ALS-inhibitor.
Be sure to use the appropriate adjuvants with any of these, and increase spray volume to 15 to 20 gallons per acre to ensure adequate coverage with Sharpen or Gramoxone.