Weather, Wind & Weeds: Keys To Herbicide Success

Now that seeding is wrapped up and we enter spraying season it is important to remember key factors for herbicide efficacy. When the weather is unpredictable, finding the proper conditions to spray in a timely matter can be a challenge. Temperature swings, strong winds, drought or excess moisture can all influence the performance of your spray application. Understanding these factors can help maximize weed control and ensure you get the most out of every application.

Temperature

Temperature influences herbicide effectiveness by affecting plant growth, absorption, translocation, and metabolic activation. Herbicides typically will be most effective when plants are actively growing. Most post emergent herbicides are most effective when applied at temperatures between 10 to 29 degrees Celsius. When temperatures drop below 10 degrees Celsius, plant metabolism slows, growth is reduced, and processes within the plant such as transpiration and photosynthesis decrease. It is important to remember not all herbicides are affected the same. The optimal temperature to spray Extendimax (dicamba) is 10 to 25 degrees, with low humidity increasing the chance of volatilization for dicamba. Systemic herbicides will be less effective as plant growth is slowed because they need to move through the plant. Typically, systemic herbicides perform better at lower temperatures than contact herbicides as excessive heat (30+ degrees) can also slow plant growth. It is important to understand how your herbicide works.

Wind

When it comes to wind, optimal spraying conditions in the wind are anywhere from 5 to 15 kilometers an hour. Anything stronger than 20 kilometers an hour it is highly recommended to park the sprayer. Completely calm conditions are not ideal as they can create inversion risks that allow spray droplets to drift unpredictably. If you are in a pinch for time, adjusting speed, dropping the spray boom or increasing the volume of water can help maintain droplet size and reduce the risk of herbicide drift.

Environment

Drought can affect plant growth which can directly influence the effectiveness of systemic herbicides. Drought influences plants (including weeds) to develop thicker, waxier leaves. This can reduce herbicide uptake for systemic products like glyphosate. If experiencing drought this season it is important to look at adjuvants or surfactants that can help penetrate thicker, waxier leaves and improve herbicide efficiency. When it comes to excess moisture, pre-emerging herbicides need adequate moisture to activate. But too much moisture can leach residual herbicides away or too deep for shallow root systems, diminishing the long-term control of the herbicide. Keep these factors in mind when spraying this season!
~Derek Keddie