I have received several questions recently about pre harvest burn down in wheat. I hear kochia is the main weed issue, but others are scattered throughout. There are a few herbicides registered for burn down in wheat, namely Aim, Ally, various glyphosate herbicides, various 2,4-D amine and ester herbicides, Clarity, Sterling Blue, and Valor. Of these, the Aim (strong) and Valor (weaker) are burners or defoliators for wheat weeds, while the glyphosate, 2,4-D and dicamba products are more systemic. Gramoxone is not registered. Systemic nature is not really an issue, as the main goal is not necessarily complete plant death, but defoliation and at least partial stem drying of the weeds. If weeds do not completely die, however, fall regrowth may be difficult to control.
Various restrictions are in place:
- Wheat needs to be at the hard dough stage before applications.
- No seed use of harvested seed recommended with glyphosate or dicamba applications. I extend this as a recommendation to all preharvest burndowns, or at least I absolutely recommend a germination test for saved seed where the use is allowed at all.
- There are straw use restrictions (do not feed) for all 2,4-D labels that I am aware of and for Clarity and Sterling Blue dicambas.
- Pre harvest intervals are shortest for Aim alone (3 days), are generally 7 days for glyphosate products and vary by other products from 10-14 days. Refer to the specific product labels for the most restrictive limiting product in a tank mixture.
Other effective use tips:
- Don't cheat on rates. Full recommendations provide the most complete burndown and defoliation.
- Watch maximum use rates per season, if preplant burndown was used. For example, the maximum total usage rate for Aim is 2 oz per acre per year.
- Use adjuvants and AMS/ nitrogen source. Follow label recommendations for use to get effective and rapid uptake.
- Use enough water. Within reason, more water will cover more growing points on the plants.
Managing weeds may not be the easiest, but if there is time, a burn down will increase harvest efficiency and post-harvest storage.