After the asian soybean rust scare hit in autumn of 2004, many of us in the sprayer industry began advocating the use of twin flat fan nozzles to better treat the disease. It turns out we were wrong. By creating two spray patterns out of one, twin flat fan nozzles reduce the force of each spray by half, meaning there is not much force with which to penetrate the soybean canopy.

The need to penetrate the canopy to get the fungicide down low on the foliage where the disease starts has been widely reported. While it’s true that twin flat fans provide excellent coverage of the upper canopy, this type of nozzle doesn’t provide much canopy penetration. Yet, some nozzle catalogs still promote the twin flat fan for this purpose.

Consider the analogy of a soft drizzle versus a hard rainstorm; the soft drizzle will merely wet the top surfaces of the plant, while a hard rain will wet the entire plant.

If penetration requires only that the spray pass conveniently through some openings in the top of the canopy, then little spray force is required. But if the spray must overcome the resistance of a fully-developed top canopy, then more force is required.

Physics Matter.

Consider the physics and separate the misinformation from the science of spray pattern dynamics as they apply to coverage and canopy penetration.

Let’s define the terms for droplet size, velocity, distance and penetration and the relationship of these factors:

Mass per unit time refers…