Interesting weather throughout the spray season has left some fields with more weed problems than normal. There is still an opportunity to keep some of these weeds from having viable seed and also help with killing the weeds to make harvest easier.
2,4-D, a growth regulator herbicide, can be sprayed on corn after the brown silk stage on most labels. Use the maximum rate for control of broadleaf weeds. Growth regulator type herbicides can kill or reduce the germination of most weed seeds provided they are not fully mature. Other herbicides used for pre-harvest weed control have to be applied after the crops are mature and in the dry-down stage.
The following are options in row crops:
- Corn – 2,4-D, Aim, paraquat, and glyphosate
- Soybeans – Aim, dicamba, paraquat, and glyphosate
- Sorghum – Aim and glyphosate
- Sunflowers – paraquat and glyphosate.
In all cases go by the rate on the label of the product that is being used. With generic products like 2,4-D, dicamba, glyphosate, and paraquat rates will vary from product to product. Remember if glyphosate was used earlier this season and did not control all the weeds it is unlikely that it will control them now. Before using any product pre-harvest make sure that the chemical that is being used is labeled to control the weeds that are being sprayed for. Make sure to follow all time restrictions before harvesting the crop. Secondly if forage is going to be used for feed or bedding from the field make sure the label does allow for this practice.
(Source – http://www.farms.com/news/pre-harvest-weed-control-in-row-crops-81727.aspx)