Tips for spraying in wind

June 11, 2014 - Issue 10

Herbicide drift injury on canola. Drift can be costly on your own farm and especially awkward and costly if it carries to a neighbouring farm.

Herbicide drift injury on canola. Drift can be costly on your own farm and especially awkward and costly if it carries to a neighbouring farm.

How do you spray weeds in a timely fashion when every day seems too windy? Too windy, according to the Guide to Crop Protection, is wind above 15 km/h. But we know that some operators will go with winds of 20 km/h and maybe a bit above. Here are tips to improve performance and limit the drift risk in wind:

Early spraying is important, so use low drift nozzles. Using a low drift nozzle so you can spray weeds early is better than waiting longer for a relatively calm day suitable for a finer spray.

Find a nozzle that can achieve a coarse spray at a broad range of pressures. But too coarse and you’re not getting adequate coverage, especially at low water volumes. Click here for a full article with images, including water-sensitive paper that demonstrates coverage based on droplet size and water volume.

Choose a nozzle that produces a coarse spray in the middle of its pressure range. A nozzle that produces a coarse spray through the middle of its pressure range gives you the most flexibility to change spray pattern and droplet size as you adjust ground speed and pressure.

Canola herbicides and droplet size.

—Glyphosate is suited to low drift (coarse droplet) sprays, but remember that at the low water volumes that favor glyphosate, coarse sprays may not provide enough droplets per square inch. A combination of coarse spray and low (but not ultra low) water volume is best to make sure you get droplets on even the smallest weeds.

—Liberty can work with a coarse spray nozzle but it needs at least 10 gallons per acre to maintain efficacy. Instead of increasing pressure to increase volume output consider using a larger nozzle. The Liberty label does not recommend using air induction nozzles.

—Group 2 products for the Clearfield system in general perform well with coarse sprays.
Click here for a more detailed article.

Aim for 100% overlap nozzle to nozzle. This provides equal coverage across the whole boom width.

Aim for 100% overlap nozzle to nozzle. This provides equal coverage across the whole boom width.

Keep your boom low to reduce drift, but make sure to use a nozzle with a fan angle to provide 100% overlap at low heights. See the image above. Spray from one nozzle should reach to the middle of the spray pattern of the adjacent nozzle.

Some breeze is good. When spraying on dead calm mornings or evenings, spray can hang in the air, making it impossible to predict when and where it will settle. (See the next paragraph for tips to identify these air inversion conditions.) A dense cloud of spray hanging in the air can do a lot of damage if carried to a neighbour’s crop or yardsite. Bright sunny days with some breeze are ideal times to spray to minimize drift damage. If those days are hard to come by, click here for tips for spraying in wet conditions.

Watch for air temperature inversions*. Early morning and evenings when conditions can be the best for spraying can also be the worst because of possible air temperature inversions. Air temperature inversions (when air temperatures rise with elevation) create ideal conditions for tiny spray droplets to become suspended in the air and drift considerable distance from their target. This cool air mass can flow like water to valleys and lower areas. The following factors often signify that an air temperature inversion is in play:

—Large temperature swings between daytime and nighttime conditions
—Very calm (<3 km/h wind) and clear conditions —Intense high pressure and very low humidity —Mist, fog, dew and frost —Smoke or dust hangs in the air and/or moves laterally in a sheet —Odours seem more intense —Daytime cumulus clouds tend to collapse toward evening, —Overnight cloud cover is 25% or less, —Soil conditions that make inversions worse include low soil moisture, freshly tilled, coarse soils, heavy residue, closed crop canopy. Tom Wolf adds that air temperature inversions don't happen during the day, with very rare exceptions related to cold air moving in from a body of water, or a strongly transpiring crop canopy. However, you can assume the atmosphere starts to become inverted as the sun sets, that the inversion will build in strength overnight, and that it reaches its peak height and severity at sunrise. Therefore, if it's late evening, night or early morning, assume you have a temperature inversion unless (1) winds are consistent and (2) cloud cover is pretty solid. Jason Deveau, a sprayer specialist with the Ontario Ministry of Agriculture and Food, recommends this factsheet from NDSU Extension Service: Air Temperature Inversions

Talk to people who might be affected. If you have to spray on days that are not ideal, talk to neighbors who might be affected by spray drift. Damaging a sensitive crop or a relationship is probably not worth the risk.

Spray apps from SSCA

Saskatchewan Soil Conservation Association (SSCA) has three smart phone apps to help with spray decisions. They are:

SSCA Spray Quality Finder: The app produces a list of nozzle candidates, and for each candidate, shows a table identifying the nozzle manufacturer, nozzle type, and model, with recommended pressures and corresponding spray qualities. The database contains all nozzle products for which spray quality information exists from TeeJet, Hypro, Greenleaf, Hardi, Wilger, Lechler, and Albuz.

SSCA Buffer Zone Calculator: Canadian pesticide labels may contain buffer zones (no-spray areas) downwind of an application. These buffer zones can be reduced if the applicator can show that application conditions are conducive to less risk than assumed on the label. This app conducts the required calculations for ground, aerial applications, orchard as well as chemigation application to determine modified buffer zones.

SSCA Tank Mix Calculator: The user enters the application volume, the pesticide and adjuvant product rates, and the tank capacity to estimate the amount of water and product required. The amount remaining in the tank at fill-up can be entered to calculate the net amount of pesticide and water to put in tank. Optional entries allow for further calculations. Supports all common imperial, US, and blended measurements units including L/acre and acres/case.

Click here to see more on the apps, and find links to download them.

*Thanks to Jason Deveau and Brian Hall from OMAFRA and Tom Wolf from AgriMetrix in Saskatoon for the inversion information.

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