As drought conditions become more frequent and intense across many agricultural regions, understanding how water stress impacts pesticide performance is critical for effective pest management. University and Extension research has shown that drought can significantly reduce the efficacy of herbicides, insecticides, and biological control agents in the field.
Herbicide Challenges Under Drought
Dry conditions cause plants — including weeds — to develop thicker, waxier leaves and slow their growth. These changes reduce herbicide uptake, especially for systemic products like glyphosate. Pre-emergence herbicides also become less effective without adequate soil moisture, as they may not activate properly or move into the root zone where emerging weeds absorb them.
Additionally, higher temperatures and low humidity increase the risk of herbicide volatilization and spray drift, leading to off-target impacts and poor weed control.
Insecticide Performance Also Drops
Systemic insecticides, which rely on plant uptake and internal movement, can lose effectiveness in drought-stressed plants. Reduced transpiration limits the pesticide’s ability to move within plant tissues, resulting in inconsistent protection and increased potential for pest survival.
Spray-applied insecticides are also more prone to evaporation and drift under hot, dry conditions, leading to reduced on-target deposition and efficacy.
Biological Controls Are Not Immune
Research into biological pest control — such as viruses used against pests like the fall armyworm — has shown that plant stress from drought can interfere with the pest-pathogen interaction, weakening control outcomes. This underscores the importance of adequate irrigation not just for crop growth, but also for supporting biological pest suppression.
What Growers Can Do
- Time applications carefully: Apply pesticides when plants are less stressed — early morning or after light rainfall can help with absorption.
- Read and follow all pesticide labels: Labels contain critical guidance, including temperature restrictions. Avoid applying pesticides, herbicides, or fungicides if temperatures exceed label-specified thresholds — often around 85°F (29°C), but this varies by product.
- Use proper adjuvants: Surfactants and other additives can improve pesticide coverage and uptake during dry conditions.
- Monitor closely: Adjust pest thresholds and scouting intensity during drought, as pest dynamics and plant sensitivity may shift.
- Integrate IPM practices: Relying solely on chemicals becomes riskier under drought. Incorporate cultural, mechanical, and biological strategies to build resilience into your pest management program.
- As weather patterns shift, adapting pest control strategies to environmental stressors like drought is essential for sustainable crop production. For more guidance, contact your local Extension office or crop advisor.
Author Rachel Maccini, Field Specialist, Extension
Additional Resources
University of California Agriculture and Natural Resources (UCANR)
