How to spot a temperature inversion
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While the early morning calm weather may appear like optimal spraying conditions, farmers run the risk of encountering a temperature inversion that could result in small spray droplets remaining suspended in the air and moving off-target. Unfortunately, post emerge herbicide timing coincides with the increased risk of temperature inversions.
How to spot a temperature inversion
Early mornings and evenings can be the most appealing, but challenging times for spraying because of air temperature inversions.
A temperature inversion occurs when a layer of warm air covers a layer of cooler air and acts like a lid, preventing the cooler air from rising and dissipating into the upper atmosphere. During a temperature inversion, spray particles can become trapped in the warmer layer of air and stay suspended until wind movement increases, resulting in off-target movement. Never spray if you suspect a temperature inversion. You risk damaging susceptible plants in nearby fields, lawns and gardens. Wait until later in the day and check again for a more favourable application environment.
It is never recommended to spray a pesticide when a temperature inversion exists, and most product labels provide guidelines to follow in order to avoid applications during one.
How to check for a temperature inversion
Follow these clues to check a temperature inversion is not occurring before every herbicide application:
- Monitor temperatures and always check field conditions.
- If temperature is within 3oC of the overnight low, closely check wind speed and particle movement in the field.
- Use smoke or powder, to indicate particle movement. The smoke or powder should drift gently with the wind. If it gathers in a stationary, suspended cloud, that indicates a temperature inversion – do not spray.
- Measure wind speed using an anemometer. If wind is less than 3 km/hour – do not spray.
- Measure the temperature at ground level (approximately 1 m or 3 ft) and at 2 m or 7 ft above ground. If the difference is more than a few degrees, it is considered an inversion.
Learn more about temperature inversions
Looking for more information about how to avoid temperature inversions and reduce spray drift? Here are a few helpful links:
- Sprayers 101blog - Thermal Inversions for Sprayer Operators
- Ontario Ministry of Agriculture, Food and Rural Affairs factsheet - Thermal inversions and spray drift