Minimising Spray Drift
Mid-North consultant, Mick Faulkner talks about the problems of spray drift, and offers some management solutions.
One of the biggest issues facing is farmers of recent times is the drift of agricultural chemicals onto susceptible crops but also into urban areas. Environmentally, we’re dropping some chemicals into resources like our rivers and streams We’re all familiar with direct drift, and that’s where we spray along a fenceline and we get drift over to the adjoining paddock.
Different Types of Spray Drift
There is another type of drift and that’s the drift that goes over many many kilometers it’s been reported drift as a result of inversion layer conditions can go for a hundred kilometers it is not as predictable like to think about where it goes because inversions chop and change in terms of the air movement.
What happens is we are producing droplets that prone to drift and then we’re getting the conditions that make them drift and the way that that occurs is when we have, we have traveling at high speeds, and when we travel at high speeds it simply means the droplet has further to go in the air, and if it has further to go, it has more chance of drifting while it’s travelling, it’s getting smaller, and as it’s getting smaller, it’s going to be picked up into the atmosphere and move off into the inversion layer, so speed is a big issue.
Spray Application Height an Important Factor
Another one is height off the ground. When we actually have the boom higher than 50 centimeters, then gravity’s still taking effect from the 20cm and we might be trying to float through 2m a meter of air to get to the target, and the droplets evaporating all that way, so it’s either gonna drift off or certainly not going to reach its target.
Really the two most important things are speed and height of the boom The third is the flicking on the ends of the boom. The wider the boom the more it flicks as it traverses at the end of the boom. throws droplets high into the air and every time that happens there’s more droplets being thrown into the air that cause a problem The issue is the droplet size itself.
Medium droplets become small droplets with evaporation pretty quickly and medium droplets on its own is quite prone to drift. When we do use very coarse to extra coarse droplets we are very confident that that we can reach the target, we can get very good weed control and we can go out and spray during the day.
From what I’ve seen the inversion layers occur in the mid north of South Australia on an average of 5 out of 7 evenings, nights and mornings during the a Summer month. Just about every day we can see we’re going to get an inversion layer unless of course there’s a continuous breeze over 11km an hour or full cloud cover.
Code of Practice for Spraying
The code of practice, that is a statewide code of practice, says not to spray within an hour and a half prior to sunset through to an hour and a half after sunrise unless there is no inversion layer, so if there’s full cloud cover at night, there’s a breeze 11 km and I feel comfortable about spraying in those conditions but as we’re getting into the afternoon, we’ve seen that the wind’s starting to drop out.
We’re pretty sure its going to be an inversion layer. It’s time to stop. Don’t be afraid of those temperatures the perhaps we are used of don’t be afraid of spraying during the day. Let’s make sure that we produce droplet sizes we maintain operating speeds of less than 18 kilometers an hour for a summer spray because the downside of all this is, unfortunately losing product.
and I don’t think any of us want to lose the products so valuable to us for spraying from spring summer and early autumn. So, let’s just keep our herbicides in our own paddocks, it’s not that difficult, we’re pretty sure that we can solve these problems of the harm that we cause to others.