Spray Volume and Droplet Size Considerations
Simer Virk and Bob Kemerait, UGA
Timely and effective fungicide applications throughout the season are an important tool for growers to
manage and protect yield from diseases like white mold and leaf spot in peanut. While selection of a
good fungicide program is critical, it is also important to ensure that the application efficacy is
maximized through proper selection of spray parameters including spray volume and droplet size. The
type of nozzle selection to attain proper droplet size has also been one of the common questions from
the Extension agents and growers in the past as well as this year. Below are few considerations for spray
volume and droplet size selection to improve spray coverage and canopy penetration in peanut along
with some illustrations:
1. Spray Volume: One of the most effective ways to improve fungicide application efficacy is by
using enough spray (water) volume. The images below show spray coverage for fungicide
applications made at three different spray volumes of 10, 15 and 20 GPA. It is obvious from the
images that 20 GPA provided the highest coverage followed by 15 and 10 GPA. It was also
noticed in these studies that the highest volume (20 GPA) also improved the coverage at the
middle of the canopy due to more volume penetrating through and into the peanut canopy. As
most fungicide labels have a minimum spray volume requirement (for ground applied) of 15
GPA to attain adequate coverage, so it is important to not use the spray volumes below the
minimum recommended since it can affect both fungicide coverage and efficacy.
2. Droplet Size: Size of the spray droplets is another important consideration for maximizing the
effectiveness of fungicide application. The images below show coverage obtained at three
different droplet sizes (medium, very coarse and ultra coarse) for the spray volume of 15 GPA.
Again, it can be seen that smaller droplets provided better and more uniform coverage while the
larger droplets, especially ultra coarse, had less and non-uniform spray distribution. It was also
noticed that the larger droplets were unable to penetrate the peanut canopy resulting in
considerably reduced coverage at the middle of the canopy. Selecting nozzles that can produce
medium to coarse droplets at the nominal operating pressure(s) is recommended to attain
adequate coverage and maximize application efficacy.
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