Drift issues have grabbed a lot of attention this year. Herbicide drift, in particular, can have a dramatic effect on your crops, and it naturally gets most of the attention when drift issues are discussed. Yet even insecticide, fungicide, or other spray material drift can create problems.
Frankly, I consider any drift to be like a white elephant gift: You shouldn’t give it, and you don’t want to get it!
Before diving into ways you can reduce drift, make sure you’re taking care of a basic maintenance issue: calibrating your sprayer one or more times a year. There’s just no excuse not to. If you won’t do it, hire someone to.
Here are four steps you can do right now — with any sprayer on most any crop — that will help reduce your spray drift.
1. Apply in the Right Wind Conditions
Do you really know the wind condition now, when you are spraying? You should. That said, it’s not as straightforward a process as it might seem at first. Here are the steps you can take to truly know what wind conditions you’re working with.
- Buy and learn to use a good quality handheld wind meter, and keep it with the sprayer.
- Document wind direction and speed at the beginning, middle, and end of the spray. Winds change. Proving you’ve stayed within label conditions is the cheapest “CYA” insurance you’ll ever buy.
- Make sure you get a good wind measurement. Structure at the field edge can block wind and fool you; the real wind speed is found six to eight times the height of any windbreaks downwind.
- Walk into the field to get a read.
- Hold the meter face height, arm’s length out, and rotate slowly to the direction the wind reads strongest. Product labels often give guidance on maximum wind speed; follow it. If there isn’t any, you’ll need to decide what’s safe for the specific application. The higher the wind speed, not only the higher the drift, but also the lower your canopy penetration will be.
A steady gentle wind is your friend. Did you know you also can have too little wind? It indicates “unstable air” that typically rises and mixes, dispersing drift quickly. Around 3 miles per hour and up, wind direction tends to become more stable too, so you can better manage where the drift might go. Below 3 mph, wind direction becomes highly variable and the turbulence dies into stability, both warning signs of temperature inversion.
Inversions can be dangerous to spray in because of the lack of air mixing. Concentrated clouds of drift move laterally, causing higher off-target residues, sometimes over long distances. It’s important to learn to identify temperature inversions.
One strong indication of temperature inversions can typically be seen in the early morning and late evening. What you should watch for is when you see fog in horizontal streaks close to the ground. That may be the only time the wind goes down enough to spray; a tough paradox in places where daytime winds can be strong. Bottom line is: Inversions increase drift risk and should be avoided.
2. Pay Attention to the “Release Point”
Everyone knows what boom height is, but most growers are unfamiliar with the concept of a “spray release point.” Once understood, it gives you powerful insight into spray placement and drift control. So what is it?
The release point is the point a droplet is released out of the spray stream into the ambient air. Where spray is released determines largely whether it becomes an effective application or a drift risk.
Coarse droplets tend to act like bullets, traveling straight from the nozzle to the leaf surface. For these, the release height is zero (the canopy surface) and thus the drift risk is low.
Many of the smaller droplets typically chosen for deep canopy coverage in veggies may slow down and release from the spray jet within 5 to 10 inches of the nozzle. High boom height, high travel speeds, or the presence of wind will all cause increasing numbers of these fine drops to release at increasing height above the canopy. The higher they release, the higher the drift risk.
Lowering the release point can be simple to complex. Here are a few ways that can be done:
- It’s not hard to get your boom down to the recommended height over the canopy, usually 20 inches, and keep it there.
- Minor hardware adaptations like changing nozzles that make larger droplets are straightforward, but can sacrifice coverage.
- Adding drop nozzles onto the boom moves spray into the lower, often poorly covered regions of the plant. Once a droplet is captured inside the canopy, there is little if any wind to drift it.
- Adding and properly using spray hoods has been shown to reduce drift up to 95%.
- Air-assisted spraying, typically requiring special machinery, also is shown to be drift-reducing when used properly.
3. Slow Down
(Full disclosure: the following requires recalibrating your sprayer.) Even half a mile per hour reduction improves coverage and reduces drift. How?
- Better boom height control, and more time spent spraying over each target, which increases your ability to push into the canopy (lower release point).
- Lower spray pressures are needed at lower speeds, creating larger droplet spectra/fewer fine droplets.
- Driving slower means producing less of your own wind. Less wind keeps the spray jet more uniform, so more small droplets get pushed down to the target (lower release point).
4. Explore Drift-Control Adjuvants
Adjuvants can be part of the drift reduction strategy by reducing the portion of spray in the smallest, highly-driftable drops.
Don’t expect a silver bullet. Just pouring a product in your tank won’t save you from poor application methods, and it may turn out you needed those fines for deep canopy coverage.
Before going all in, get compatibility data from the supplier for your conditions, chemicals, and crops; experiment a bit, and do your homework.
With these tips (and a calibrated sprayer) you’ll be sharing more vegetables, and less spray, with your neighbors this season.