Weed control strategies for drought affected fall crops

By Blake Jackson

Drought in Pennsylvania has raised concerns about the effectiveness of herbicide applications on fall crops and weeds. While the cooler temperatures may mitigate some of the heat stress experienced during summer droughts, the lack of rainfall can still impact both crop and weed growth.

Soil-Applied Herbicides and Rainfall:

For soil-applied herbicides, adequate rainfall is crucial for activation and weed control. If rainfall is delayed, the effectiveness of these herbicides may be compromised, especially for emerged weeds. Post-herbicide rescue applications may be necessary in such cases.

Crop Injury and Post-Herbicide Applications:

Drought stress can make crops more susceptible to herbicide injury. To minimize risk, avoid combining multiple herbicide applications and adjuvants in a single tank mix. Stick to essential products and consider reducing rates if necessary.

Weed Response to Drought:

While some weeds, like common chickweed, annual bluegrass, and downy brome, are sensitive to drought, others, such as marestail, quackgrass, and Canada thistle, are more tolerant.

The growth and susceptibility of weeds to herbicides can vary depending on their specific characteristics and the severity of the drought.

Herbicide Application Considerations:

• Timing: Apply herbicides when daytime temperatures are above 50°F and nighttime temperatures are above 40°F to ensure optimal activity.
• Adjuvants: Use adjuvants as recommended on the herbicide label to enhance efficacy. Consider using MSO or COC adjuvants in drought conditions to improve herbicide uptake and control.
• Herbicide Selection: Choose herbicides that are effective against the target weeds and have a lower risk of crop injury under drought stress.
• Application Techniques: Proper calibration and application techniques are essential for effective weed control and minimizing environmental impact.

By carefully considering these factors, farmers can make informed decisions about herbicide applications during drought conditions and protect their crops while minimizing environmental risks.

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