Spraying in adverse conditions

Finding the best time to spray to get the most coverage and action can be a challenge for farmers. 

One of the biggest challenges for farmers when spraying is the wind.

Dr Tom Wolf, a research scientist and co-owner of Agrimetrix says we're fighting wind all the time and there's really not much we can do.

He says they went back into their data for spray drift to look at what happens to the droplets when the wind takes them away.

"The answer is that more leaves, but the coarser we spray, the less leaves. So we do have that opportunity, lower booms, slower travel speeds. Those are the big three that help. The other thing we looked at in the data was where does the spray go after it leaves? It turns out that if it's windy, the spray doesn't necessarily cause as much downwind damage as we think. The damage is about neutral, so it's not great that we're losing more spriters, but it's also not necessarily a big threat to our neighbors, provided we do something about it."

He points out that for years we've been telling farmers to spray when it's calm - early morning or late evening, but now we're realizing that might not be the best time.

"The fact of the matter is when it's windy, the atmosphere is turbulent, so it mixes the spray cloud into the atmosphere and dilutes it. It doesn't come down to the ground that concentrated, it doesn't cause that much damage. So actually, spraying in the wind is a better option than spraying in the calm because the calm in the early morning/late evening when we traditionally look for those calm conditions is associated with temperature inversions, in which case the damage can be much worse, much more widespread."

He says every summer night is a potential for an inversion. So it's risky to do that, especially when we're diversifying into lentils, where the price is pretty good right now, and we're spraying with volatile products.

"So we want to avoid the situations that will cause damage to our valuable crops and that means avoiding inversions. Better to spray when it's a little breezier and then use the three methods I mentioned, coarser spray, lower booms and slower travel speeds. Particularly in the outside rounds to protect your neighbors crops."

So what kind of wind speed is safe and what's the cutoff?

Wolf says there's no hard and fast number on that he's as perplexed as everyone else about giving that number as it depends on what's in the tank and what's downwind.

For more information and tips on spraying visit the Agrimetrix website "Sprayers 101".