Precautions for Post-emergence Herbicide Application on Corn Seedlings

The period of 2-10 leaves after emergence is a critical time for weed control in corn. Every year, corn growers in different regions use post-emergence herbicides, but they often encounter issues such as herbicide damage to corn, ineffective results, and sometimes the weeds survive while the corn is affected. This can be quite frustrating for farmers. Today, we will discuss the best and safest timing for post-emergence herbicide application on corn, how to achieve the best results, the optimal spraying time, spraying methods, precautions, and how to identify the leaf stage of corn.


Best Timing for Spraying Post-emergence Herbicides on Corn

The best time to apply post-emergence herbicides on corn is when the corn has 3-5 leaves, and the weeds are at the 2-4 leaf stage. After the six-leaf-one-tassel stage of corn, be cautious when using herbicides like nicosulfuron and MCPA to avoid damage. Topramezone has relatively higher safety and can be sprayed later.


Precautions for Spraying Herbicides on Corn

(1) Ensure that most of the weeds in the field have emerged, and spray when most weeds are at the 2-4 leaf stage. Spraying too late may result in increased weed resistance and reduced herbicidal efficacy.

(2) Spray when the temperature is between 15-25°C, relative humidity is above 65%, and wind speed is below 3 on the Beaufort scale. Use appropriate spraying equipment and nozzles following the spraying operation standards.

(3) Dilution: For machine spraying, dilute with 700-900 pounds of water, ensuring uniform and thorough coverage.


How to Identify the Leaf Stage of Corn

During the herbicide spraying stage, it is essential to determine the fully expanded leaves. The best time for post-emergence herbicide application is when the corn has 3-5 leaves, and the weeds are at the 2-4 leaf stage. How can we determine the leaf stage of corn?

Usually, the number of fully expanded leaves on the main stem of corn is used to define the leaf age. Fully expanded leaves refer to leaves that have completely unfolded, showing clear leaf collars and leaf auricles at the junction with the stem. In the early growth stage of corn, the number of leaves is relatively complete, so we can judge the leaf stage based on the number of fully expanded leaves. In the image below, there are three fully expanded leaves, so we determine it as the 3-leaf stage.

Note: This method can accurately determine the growth stage of corn. However, the developmental stages of all corn plants in the same cornfield are not entirely consistent. When more than 50% of the plants in the field are at the same stage, it is considered to be at that corresponding stage. The third leaf collar of the young seedling emerges from the collar of the second leaf, indicating the 3-leaf stage, and the leaf stage is 3. Typically, this occurs around 2-3 weeks after sowing.

4. Recommended Post-emergence Herbicide for Seedlings

For corn at the 3-5 leaf stage, we recommend using Mesotrione + Atrazine 55% SC. This product is a specialized herbicide for cornfields and can effectively control various annual weeds, including barnyard grass, goose grass, purslane, crabgrass, and green bristlegrass. It has a broad spectrum of weed control, long-lasting effectiveness, and fast herbicidal action. Additionally, a dedicated adjuvant is added to enhance penetration and accelerate the herbicidal effect.

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