When applying fungicides to control rust in soybeans, both coverage and canopy penetration are critical. Achieving this usually will require some changes from the traditional sprayer setup, including:
Different spray nozzle tips
Different spray carrier volumes
Different spray pressure
Different orientation of the spray tips
Slower travel speed
Most labels recommend using 10-20 gallons of water per acre with the fungicides for ground applications and 5 gallons per acre for air applications. Always follow label directions. Higher carrier rates improve coverage and penetration. Remember, to control rust its critical that you cover as much crop foliage as possible. Many producers are most familiar with spraying for weeds and insects where an average spraying performance may provide satisfactory results. This will not be the case for preventative and rescue rust treatments.
While fine spray particle size provides the best coverage and penetration, you might consider nozzles that produce particles in the medium size category. While very small spray droplets can increase coverage, they are susceptible to off target movement and evaporation. If nozzle tips are available in stainless steel or ceramic, they probably are your best investment because of their excellent wear life.
To increase penetration and coverage, angle the spray tips back 45 degrees and ensure that the height of the spray boom provides 100 percent overlap at the target height the top of soybean plants. If you have to use a higher boom height, reduce the angle to less than 45 degrees so the pattern provides a 100% overlap. One hundred percent overlap is where the pattern from the nozzle tip ends up under the next nozzle.
Cooperative Extension NebGuide G1548, Spray Boom Set-Up for Field Sprayers, is helpful for making these boom adjustments and changes.
Dave Varner is an Extension Educator with the University of Nebraska Cooperative Extension office in Dodge County. Dave may be contacted at 727-2775, 1206 West 23rd Street in Fremont, or at dvarner1@unl.edu
