We are beginning to see flag leaves emerging in some of the more advanced wheat fields. This is an important step in the development of the wheat plant. It is also a critical period in herbicide application. Once the flag leaf emerges, there is a direct channel down into the whorl to the developing head. Phenoxy based chemicals (Badge, 2,4-D, Estaprop, MCPA) can damage the small developing head, resulting in poor seed development and yield loss. If you are still considering spraying, the risk of yield loss due to weed pressure needs to be weighed against the potential yield loss from crop injury.
The extent of the crop injury cannot be determined prior to spraying. It is affected by crop stress, the chemical being used and the crop stage of the wheat. The plants ability to metabolize chemical is based on its growth rate. A plant stressed due to drought, excess water or extreme temperatures may not be able to metabolize the chemical quickly enough, resulting in increased crop injury. There is a risk of injury from all phenoxy herbicides but the hotter chemicals such as Estaprop have an increased risk of doing damage versus a milder phenoxy like MCPA Sodium. The plant is developing quickly at this time and the difference from one day to the next may be enough to expose the head to chemical exposure and damage.
While weed control is important to crop growth and harvestability, once the flag leaf is out, you must weigh the cost of crop injury versus yield loss from weed pressure. If weed growth is heavy, the better option may be apply a pre-harvest burn down once the wheat has reached maturity. Contact your Veritas team if you have any questions.
Veritas – May 2014