Applying insecticides and fungicides to large soybean plants is much different than applying systemic post-emergence herbicides to weeds that are 2 to 4 inches tall.

In fact, entomologists and pathologists don’t recommend tank-mixing herbicides with insecticides or fungicides due to the timing and application incompatibilities.

Producers need to be aware of the key differences and make the necessary equipment and operating adjustments to maximize insect and disease control in soybeans.

Leaf coverage is much more important with insecticide and fungicide applications than it is with systemic herbicides.

Another key difference is that insecticide and fungicide droplets need to penetrate large and dense soybean canopies.

The following recommendations will help you achieve the canopy penetration and leaf coverage required for good insect and disease control in tall and dense soybeans.

Spray volume has the greatest impact on canopy penetration and leaf coverage. Increasing spray volume increases penetration and coverage.

Spray volumes of 15 gallons per acre are required when applying insecticide and fungicides to soybeans through growth stage R3 (pod development). After R3, 20 gallons per acre are necessary.

Droplet size is the second most important factor affecting canopy penetration and leaf coverage. Small droplets provide the best leaf coverage, but lack the momentum to penetrate the canopy.

Large droplets easily penetrate the canopy, but don’t provide adequate leaf coverage.

Research has shown that fine to medium droplets having volume median diameters (VMDs) ranging from 200 to 350 microns will provide the optimum canopy penetration and leaf coverage.

All nozzle manufacturers use a common spray quality classification system that divides droplets into six droplet size categories.

Ground speed is an important consideration as it affects spray volume and vertical droplet velocity.

As ground speed increases, spray volume per acre and vertical velocity of the droplets decrease, reducing canopy penetration. Ground speeds of less than 10 miles per hour are recommended.