Mike Roberts

Getting Herbicide Applications Right on Time

Timing for herbicide applications starts to get tricky once Florida’s rainy season gets underway. Florida’s May-to-October rainy season brings nearly daily rain showers that can both delay herbicide spraying and decrease the effectiveness of the herbicide through reduced absorption and translocation. Timing your herbicide applications just right can help maximize the application’s effectiveness and reduce waste and herbicide movement.

Tips on Timing Herbicide Applications

  1. Know the weather. The most important tip is to keep an eye on weather forecasts to monitor current and upcoming weather. The UF/IFAS Florida Automated Weather Network (FAWN) weather app offers information on current rainfall, current wind speed, 7-day rainfall, radar, and rain forecasts—just to name a few—from weather stations across the state. 
  2. Know the “rainfast period” of your herbicide. Knowing the rainfast period is also very important; it is the interval required between herbicide application and any water touching the leaves—such as rain or overhead irrigation—that is required for the herbicide to be absorbed by the plant for optimal efficacy. Many post-emergent herbicides used in citrus have a rainfast period of half an hour to an hour, though some are as long as six hours. Each herbicide has a different rainfast period; You can find it on the product’s label. Rain that occurs within the rainfast period will dilute and compromise your herbicide’s efficacy, meaning during the rainfast period is not the “Right Time” to apply the product when viewed through the 4R lens.
  3. Do not spray immediately after rain. The plant’s leaves must be dry before applying an herbicide or the application will not be as effective. Water on the plant’s leaves will dilute the herbicide and compromise the herbicide’s effectiveness. Spraying herbicide after rain will also have the undesirable effect of moving the product into the soil and possibly into groundwater, and the cost of the product will be lost as well.
  4. Don’t try to fit an herbicide spray in between rain showers. Leaves must be dry during application and the product must have time to be absorbed. Again, this will also waste herbicide and introduce it into environments where it is not needed nor wanted.

Pay attention to windy conditions. Too much wind will cause herbicide drift, which means your sprayed herbicide can drift and settle on something other than your target, such as your citrus trees or other crop, your neighbor’s field, etc. Spraying herbicides during windy weather can damage your crops, waste your product, and put herbicide where it shouldn’t be. Windy weather, either with or without rain, is also not the “Right Time” to apply herbicides.

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