Pro and custom applicators understand that their methods play a big part in how successful and effective they are at making a crop chemical applications. And, they know that a successful spray must also use their time, chemicals and water resources efficiently, and limit any environmental impact. So what is the right way to apply a pesticide or herbicide?
To answer the question properly, you need to look at four factors:
Canopy
Water volume
Target type and droplet behavior
Mode of action¹
To start, look at the crop canopy to be sprayed. If it’s an early season spray into a seedling crop, then the canopy won’t provide much of a barrier. Therefore, think about using a lower water volume. Droplet size will depend on the crop and the mode of action.
If it’s a later-season application into the bottom of a maturing canopy, the foliage may intercept the spray before it reaches the target area. You might need more water, and droplet size may become more critical for getting the spray to its destination. Dense canopies can be a significant challenge. Lower canopies usually benefit from finer sprays because small droplets can better turn corners around foliage.
Regardless of canopy, the “right way” is a range of application possibilities, and will depend on water volume and spray quality combination. It’s simple math: Assuming some constant amount of coverage on each leaf, more layers of foliage will require more water. Using less water volume will make it necessary to use finer sprays to keep droplet numbers constant. More water will allow coarser sprays. This decision has implications for spray drift, and by extension, impacts the number of hours you can spray in a day. More drift tolerance means better application timing and overall productivity.
Source: Wolf, T. (2015). Deciding on the Right Way to Spray. |
Whatever spray you use, the target plant and/or insect or weed needs to intercept, collect and retain the spray droplet. Target leaves may be vertical or horizontal, large or small. Their waxy surface may be easy-to-wet or difficult-to-wet. The general rules of thumb are: Larger, more horizontal and easy-to-wet surfaces are better suited for coarser sprays – they are intercepted more efficiently and stick readily¹. That’s one reason why most broadleaf weeds and crops are very compatible with low-drift sprays.
On the other hand, smaller, vertically oriented and difficult-to-wet plants require finer sprays for effective targeting. Larger drops tend to miss these targets or bounce off them. Most grassy, and some broadleaf weeds (especially at early growth stages), fall into this category.
Source: Wolf, T. (2015). Deciding on the Right Way to Spray. |
You’ve heard “mode of action” when discussing herbicides, pesticides and fungicides. But what exactly is a mode of action (MOA)? To begin with, the MOA is the way in which the herbicide/pesticide/fungicide controls the target. It also generally describes the biological process or enzyme that the chemical interrupts, affecting normal growth and/or development of the target. Sometimes, the MOA might be a generalized description of the symptoms seen on vulnerable plants².
There are nearly 30 MOAs in the herbicide world, another 10 modes for insecticides and 15 for fungicides. Knowing a little bit, generally, about each MOA is a critical step in choosing the proper herbicide, pesticide or fungicide for each crop, as well as diagnosing crop injury and designing a crop management program you can implement effectively. Also, over-reliance on a single MOA—or active ingredient—may lead to herbicide resistance over time².
For starters, the impact of droplet size and water volume on uptake and translocation (the movement of the chemical from leaves to other tissues in the plant) varies among MOAs, so it’s important to recognize and consider this when using various MOAs. We’ve said it a lot, but the best source of information will always be the product’s label.
Successful DIY sprayers establish a good routine but plan for the unexpected. Not all, but many farming operations are making the same type of routine applications that are broad-spectrum, targeting large and small broadleaf and grassy plants. You want to establish a good working process to approach all of your spraying applications, with enough time for preparation and planning up front, but plan for flexibility when things you cannot control undoubtedly pop up.
Many sprays include tank mixes of several modes of action. Keeping detailed records, testing before you spray and understanding how each MOA and tank mix partner interacts—both in the tank and when sprayed on the crop—can make all the difference.
You may have to adjust your plan if you incorporate a new cover crop or plant a new seed variety. This depends on your crop rotation. Every consideration in your cropping plan can impact your chemical management plan and thereby your approach to your spraying applications.