A few years ago, temperature inversion was a common winter meeting topic. The themes often centered on spray drift during a temperature inversion or volatility occurring after spraying. These topics are still major points of discussion at the farm gate today. However, it is important to understand that temperature inversions and volatility are two very different occurrences.
Volatility occurs when a liquid, such as an applied herbicide, converts to a gas before becoming suspended in the air. The gas can potentially move off-target while suspended. On the other hand, a temperature inversion occurs when cooler air lies below warmer air near the ground surface. For example, if you watch smoke billowing from a chimney in the morning and it stays in a horizontal line as it travels, that is indication of a temperature inversion. Basically, the inversion prevents liquid from falling to the ground, suspending the material in the air. Figure 1 shows typical conditions versus those prevalent during a temperature inversion.
Volatility, or the suspension of a product such as an herbicide, is a big deal for agriculture. There are many products like dicamba, 2,4-D, and glyphosate that can cause major problems if suspended and move (blown) off-target from the intended pest. Even a slight wind can move suspended herbicide droplets to another location. This can become a problem if the herbicide moves to a susceptible crop and results in crop damage.
Temperature inversions can be mitigated by closely monitoring the weather along with the timing of the application. Inversions can be discovered by measuring the temperature within a foot above the soil surface (if crops are not emerged) and taking another measurement of temperature at around 8 to 10 feet in the air. If the temperature is higher at the 8 to 10 feet range, an inversion is present. As the difference between the two temperatures increases, so does the inversion intensity. Some other conditions that may indicate an inversion is the presence of mist, dew, fog, frost, a wind speed below 3 mph, distant sounds that become easier to hear, or cumulous clouds that spread as evening occurs. Observing these conditions can provide advance warnings to applicators as they monitor weather conditions.
As technology changes with agriculture pesticides, our need to be more aware of weather, application timing, and application requirements, increases. There are always challenges within the industry around growing crops. If we can mitigate risk by adhering to the correct product specifications and eliminate tasks that are not recommended, we can minimize the occurrence of instances where temperature inversions and damage caused by volatility result in problems for the agriculture industry.
For additional information, please see Channel® Advice, Air Temperature Inversion Effects on Pesticide Spray Drift.