Blog: The Wheat Sheaf

Scheduling Spray Operations when Time is Short: 10 pointers for prioritizing the tasks to ensure everything gets done with the least risk 

It’s a common problem with farm work.  Too much to do, not enough time to do it in. In an industry where everything we do is time sensitive, the stakes are high. Marketing grain. Purchasing inputs. Seeding. Spraying. Harvesting. A few days outside of the optimal timing window for any of these activities can be costly in terms of yield, grade, ease of harvest, overall return.

Let’s look at spraying in particular. It’s not uncommon for the weather to offer very narrow windows of opportunity, especially in a year when seeding started late and plant development tends to be faster. It’s often too windy, too wet, or too hot to get the job done, or the crop may be in the wrong stage. What are some guidelines for prioritizing the tasks to ensure everything gets done with the least risk? Here are some pointers:

  1. Maintain an active scouting schedule. Awareness of the crop or pest stage is essential. Things happen fast during the growing season, and a crop or weed growing out of its staging window is all too common. Scouting creates a list of priorities. Identify the urgency, in days that treatment must occur.

  2. Use a trusted weather forecasting system. Good weather is the main go-ahead factor for a spray operation. Understanding approaching weather systems is essential to scheduling the tasks. Some products require rain to be activated. Others have long rainfastness requirements. Very importantly, some products can be sprayed with coarser sprays without loss of efficacy, and those can be left for the higher wind conditions. We’ve been using Windfinder or Ventusky for their tremendous graphics that show wind speed and direction trends over time, at 1 h intervals.

  3. Be aware of the surrounding areas. What product are you planning to spray? Are neighbouring crops sensitive to this product, or doe they have MRL issues? What are the acceptable wind directions or speeds for this situation? It’s frustrating to have everything ready and find that the downwind area won’t permit a safe application.

  4. Consider the entire range of products that are suitable for your situation.  Some modes of action allow for coarser sprays, or have lower risks if they do drift. For example, glyphosate, Group 2, and Group 4 products can be sprayed in remarkably coarse sprays, Extremely Coarse is usually acceptable and works reliably. This provides an opportunity for spraying under somewhat windier conditions. Obviously downwind sensitivities matter a great deal, so do your homework.

  5. Save contact products for calmer days. Products that should be sprayed with finer sprays include Group 1, 6, 10, 14, and 22. These are all essentially contact modes of action. On the fortunate side, few of these are implicated in drift complaints because their effectiveness at low doses usually drops off very rapidly. Nonetheless, wait for better conditions to apply these so that the finer spray/better coverage can be achieved.

  6. Don’t be tempted to spray under inversion conditions. Late evenings, overnight, and early mornings under clear skies are high risk for inversions. The risks are very high. Buoyant spray droplets don’t disperse in inversions, and can concentrate at the bottom of sloped terrain. On flat terrain, they can linger for long periods of time, even reversing direction, and cause significant and widespread damage.

  7. Wind isn’t all bad. While we don’t advocate for spraying when it’s windy, those conditions do have some advantages over inversions
    •  Wind direction is relatively certain, so sensitive areas can be avoided.
    • Mechanical turbulence disperses the spray, making it less potent
    • If it’s also sunny, thermal turbulence enhances dispersion even more than mechanical turbulence
    • You can adjust machine settings to minimize drift risk, such as lowering booms, slowing down, lowering pressure, adding water volume, selecting a coarser    nozzle.
    • Drift deposits diminish very rapidly with distance. A buffer strip allows you to get the majority of the work done while protecting sensitive regions.
    • Consider productivity enhancements. Improved filling and cleaning procedures save time and make the most of the weather you have. We’ve written about these on
  8. Consider productivity enhancements. Improved filling and cleaning procedures save time and make the most of the weather you have. We’ve written about these on

  9. Consider a checklist. Sure, you’re a pro. But when time is at a premium, don’t risk not having all the supplies needed for filling and cleaning, spare nozzles and bodies. Stopping to wait, or a trip back to the yard, should not be necessary.

  10. Don’t clean plugged nozzles. Save them for later cleaning and simply replace them with a new one that you brought along.

A properly prepared operator will have a list of fields and their required treatments, and the optimal date for application. Someone who is more prepared will identify sensitive areas near those fields. Finally, the expected wind directions in the short and reasonably longer term will identify a window where those sites can be treated. Match modes of actions with coarser sprays where possible and allow those to be applied on windier days if necessary. Be prepared enough that good spray weather isn’t wasted on non-spraying tasks. And finally, be creative when pushed into a corner. Go slower, lower the booms, use more water, and get a set of low drift nozzles for that field that must be treated before the next rain.  Call the field owner if you’re concerned about potential damage downwind. That courtesy may be very helpful later.

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