By Dallas Peterson
Once again it appears that weeds are going to cause harvest problems in wheat. Thin stands from winterkill in some areas and the abundant rains in May and June have resulted in weeds showing up in many wheat fields, especially if not treated earlier. No one wants to spend extra money on a below-average crop, but these weeds can make harvest very difficult.
Unfortunately, there aren’t many good options at this point in time. There are also a lot of questions about which herbicides are approved and the “use guidelines and restrictions” for pre-harvest treatments in wheat. Listed below are the various herbicide options growers can use as pre-harvest aids in wheat. There are differences in how quickly they act to control the weeds, the interval requirement between application and grain harvest, and the level or length of control achieved. All of them will require good thorough spray coverage to be most effective.
Sharpen is now labeled for use as a pre-harvest treatment in wheat and is approved in North America, but is not included in the table because it does not have Maximum Residue Limit (MRL) approvals for use as a pre-harvest wheat treatment in some key export markets. Some grain marketers have indicated they will not accept wheat that was treated with a pre-harvest application of Sharpen, so it is not being promoted for that use at this point in time.
Please note that the 2,4-D rate approved for pre-harvest weed control in wheat has been reduced to a maximum of 0.5 pound per acre, which is equal to 1 pint of a 4-pound formulation or two-third pint of a 6-pound material. 2,4-D also has a 14-day pre-harvest requirement.
Another herbicide that is sometimes mentioned as a possible pre-harvest treatment is paraquat. Paraquat is not labeled for pre-harvest treatment in wheat. Application of paraquat to wheat is an illegal treatment and can result in a quarantine and destruction of the harvested grain, along with severe fines.