Below is an overview of some options to consider for preharvest weed control in small grains. However, before applying any product, here are a few considerations:
- This may be a great opportunity to control perennial weeds prior to double crop soybean or prior to establishment of a late summer hay crop or covers. Although late summer/early fall is still the best time for perennial weed control, this is certainly better than early summer applications and may help fit into certain crop rotations.
- Don't expect miracles with harvest aids. It is still easier to control smaller weeds (less than 4 inches tall) than larger ones (2-3 feet). In some cases, the lower portions of the weeds may still be green and unaffected.
- It takes time to bring down a large weed. It usually requires about a week or more to obtain good control or dry-down of some weeds. This time may increase if cool/wet weather conditions prevail. Some of the small grain herbicides labeled for preharvest are systemic and slower-acting than a contact herbicide.
- Harvest aids are meant to help facilitate harvest and reduce harvest loss. Any yield loss is likely already due to weed competition throughout the growing season. Also, any weed seeds produced will contribute to next year's weed problems.
- Harvest aids are not intended to (and usually do not) help speed up crop maturity. If applied too early, they can interfere with the natural crop maturation process. Illegal herbicide residues can result if specific application timing and other label guidelines are not followed. See the specific product label to determine the correct rate, timing, weed species controlled, and other restrictions with this type of application.
- Herbicide drift from these applications at this time of year will cause injury/death to sensitive crops/plants in surrounding areas.
- Adhere to all restrictions regarding grazing and feeding of straw for each of these products.
2,4-D
Some formulations of 2,4-D ester are labeled for preharvest applications in wheat, barley, oat, and rye. (Only certain 2,4-D products have all of these small grains listed on their label under preharvest, so consult the specific label before application.) Use 1 to 2 pints per acre depending on the product (no adjuvants are recommended). Applications should be made after the small grain is in the hard-dough stage and at least 14 days before harvest. Do not apply to small grains with a legume underseeding. If a preharvest application of 2,4-D ester is made, double-crop soybeans can be planted 7 days later for 1 pint or 30 days for 2 pints. 2,4-D is volatile and can potentially damage nearby sensitive crops. Avoid use if temperatures are expected to exceed 75°F. (Enlist One/Duo and Freelexx are not labeled for this use.)
Source : psu.edu