While herbicides are often an ally to cornfields by controlling competitive weeds, they can also cause injury if not applied properly. An incorrect herbicide application, off timing, spray drift, an excessive rate, an incomplete tank cleanout or carryover are all potential suspects for herbicide injury.
Understanding how herbicides manage weeds is useful for selecting the proper herbicide for your fields, managing resistant weed populations and diagnosing herbicide injury. To help determine exactly what happened, it’s important to first be aware of the herbicide mode of action applied. Having this information at hand will help you diagnose the symptoms of herbicide injury.
There are two herbicide modes of action – contact and systemic. Contact herbicides are not able to move within a plant, so are therefore highly dependent upon uniform coverage of treated soil or plant tissue. Systemic herbicides are distinguished by the crop’s ability to metabolize the herbicide as it moves throughout the various plant parts. Regardless of mode, injury symptoms are often most prominent where the herbicide is concentrated.
Particular weather patterns can increase the likelihood of crop injury from post-emergent herbicides. If applications are made as the days turn hot and sunny, the risk of damage is greater because the waxy leaf layer has not developed. This results in the plant surface being more tender and susceptible to injury.
If you have to spray during these weather conditions, switch to a “softer” additive if the label allows. For instance, use a crop oil concentrate over a methylated seed oil. But first, be sure to read the label and see what is allowed by the manufacturer.
In the case of herbicide injury, there is oftentimes little that can be done to remedy the situation right away. With this constraint in mind, ask the right questions to determine if herbicide injury is really the case. Nutrient deficiencies, fertilizer burn, compaction or disease can all show symptoms similar to herbicide injury. You will want to rule those out before proceeding.
To ensure your fields are free of herbicide injury, scout throughout the season from emergence to tassel. While walking your fields, keep in mind early herbicide injury can leave plants susceptible to later issues like greensnap, inadequate root development, stand loss and shortened internodes. During the pollination and grain fill stages, inspect your crop for pinched ears and missing or aborted kernels. Right before harvest, check for ear retention, standability or stalk integrity issues.
Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.
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