As crops continue to grow and post emergence spraying is in full swing, the risk of spray drift increases. Over the last few days I have looked at more than one spray drift issue. While you may chuckle at sayings like “spray drift is a great way to meet neighbours”, the truth is, spray drift is a serious and potentially expensive issue.
There are two types of spray drift, particle drift and vapour drift. Particle drift results when small droplets are blown by wind to non-target areas. This can be minimized by increasing droplet size, decreasing spray pressure and only applying when wind speeds are low. Vapour drift occurs when chemicals volatilize or evaporate off the crop or soil as temperatures rise. This tends to be more prominent with certain chemicals. The label will provide any warnings or precautions to reduce this risk. Vapour drift is more likely when conditions are hot and dry.
Nozzles directly influence the droplet size. Larger particles reduce the risk of drift but may decrease the efficacy of the chemical. This is often the case with fungicides or foliar contact sprays. The product label will let you know if specific nozzles or droplet sizes are needed. Inspect nozzles for blockage or wear. Output for each nozzle should be within 5% of the recommended nozzle rate. Increased boom height will increase drift potential. Keep boom height only as high as needed to ensure good coverage.
Always measure wind speed and direction before, during and after spraying and always keep records. Be aware of any surrounding sensitive crops or public areas. A simple wind meter is an excellent investment for the sprayer. This is a link to a company named Kestrel that make a wide variety of cheap and effective wind meters that can be ordered on line. http://kestrelmeters.com/ Wind speeds between 3-7 mph are preferred but check the label for any product specific information. If wind speeds exceed 10 mph or wind changes direction, change buffer distances, move to a new location or stop immediately.
Temperature inversions occur when warm air rises and cooler air settles to the ground. These conditions often form at dusk and breakup at sunrise and can produce what we see as ground fog. When these conditions occur, there is no mixing of air and spray droplets do not disperse. They remain concentrated near the ground and can move with airflow to off target sites. Be aware of these conditions, especially when spraying at night.
As the operator of the sprayer, you are responsible for any drift problem, even if nature is the cause of the issue. Read the label, check your equipment and beware of environmental conditions. Always consider your safety, that of others and the safety of the surrounding area. And above all, never forget to use your common sense. If you do not have a label or have any questions, contact your Veritas agronomy team for more information.
Jason Van Maanen
Veritas – June 2014