Pre-harvest weed control for small grains

Farm Forum

The rains that lasted up until a few weeks ago have tempered to much drier conditions recently, but that moisture resulted in a flush of weeds in a number of wheat fields. Mixed reports can be found among combine operators as to the problems that weeds pose during harvest operations and the help that pre-harvest weed control provides, but dense weed infestations may justify an herbicide application. If they haven’t already gone to seed, noxious weed infestations should definitely be treated. Factsheet FS953, “Harvest Aid Weed Control for Small Grain” is a resource that has been around for a few years, but is still valid regarding the herbicides that are available, recommended rates, timing of application, and other considerations. The document is available at your SDSU Regional Extension Center, your local County Extension Office, or online at:

Herbicide options include: several 2,4-D Ester or Amine products, Dicamba (Banvel, Clarity or Sterling), Ally, Aim, and a number of Glyphosate products. Several options allow tank mixing with other labeled products, and many do not allow feeding straw or grazing stubble from treated fields. Some of the products are not recommended for seed fields, or extra caution is recommended so that they don’t go on too early. The time between application and harvest ranges from as little as 3 days to a maximum of 10 days.

The hard dough stage, or less than 35% kernel moisture, is the earliest recommended time for application for at least some of the products. Earlier applications are particularly risky when plans include keeping the crop for seed. Research showed that 81% of the seedlings grown from a crop that received a glyphosate application at 50% seed moisture were abnormal and 3% were nonviable. When glyphosate was applied at less than 35% seed moisture, only 2% of the seedlings were abnormal and 1% were nonviable. Wheat seedling emergence was not affected by most of the other pre-harvest treatments of application timings.

Other strategies include windrowing, or simply straight cutting through the weeds.

Read and follow label directions and use caution to avoid drift to adjacent crops when pre-harvest spraying.