Aerial Spraying of Asian Soybean Rust

Asian Soybean Rust is being found in more and more locations in the United States, with new locations in the southeast showing up almost daily as this article is being written. Wide spread infestations may not occur or be too late to have a major impact on this year’s crop. Aerial applicators need to be prepared to respond though when, or if, applications are needed. Spraying for “Rust” is somewhat new, but applications of fungicides certainly is not!

There are a new publications coming out daily with recommendations on Asian Soybean Rust control. These may not all be in agreement on exactly how to accomplish this task but a key in all is the need even and complete coverage of the complete plant – no matter what type of spray platform is being utilized. It is essential to get as much material in the lower portions of the plant canopy as possible, because this is the area that is most susceptible to Rust establishment.

CP Products nozzles are one of the most flexible on the market. Utilizing the correct setting is key to obtaining the correct droplet spectrum. Medium category sprays in the range of 250 to 300 microns, VMD, are expected to have the best results. One would utilize the upper end of this range when there is a need to spray in hot-dry conditions (temperatures > 85ºF and with relative humidity of 60% or less).

Too Fine – When droplets are too small they have a very difficult time reaching down in the canopy. Convective currents may simply carry them away or evaporate them prior to deposition. Slight changes in droplet diameter significantly changes the droplet mass. Slight increases in droplet diameter may increase the mass enough to carry them down into the canopy.

Too Coarse – When droplet size is increased too much, many may end up on the ground or only on a portion of the plant surface. Also as droplet size increases, there are simply not enough droplets to obtain thorough coverage of the plant surface. As an example: 300 micron droplets have 72% more mass than 250 micron droplets (581 - 300 micron droplets have the same mass or water as 1000 – 250 micron droplets).

Water volume is important – but high volumes may not be necessary. There needs to be enough diluent carrier to develop the correct droplet spectrum and have enough droplets at that size for coverage. Field evaluations have shown that excellent results may be obtained with as little as 3 GPA, but 5-7 GPA is typically recommended in the USA from the conservative side. Total water volume must also be tempered with the plant foliage condition. Tall plants that are completely closed up simply have more surface area to cover and may need more droplets. When spraying early in the plant growth stages, there simply is not as much surface area to cover. Any application volume may fail if the droplet spectrum is either too large or too small!

Remember to calibrate properly and pattern test for uniformity and correct swath width!

Utilize the CP Nozzle Comparison Table to help you select a setup for CP nozzles that will result in a droplet spectrum to optimize foliage deposition. For metric, click here.