This blog is dedicated to sharing timely and relevant precision ag information with county Extension agents and growers.

For peanut growers, timely and effective fungicide applications throughout the season are an important tool to manage and protect yield from diseases like white mold and leaf spot. Considering the recent rains and wet field conditions, peanut growers are likely already behind and may have missed few fungicide applications. Because of this, the importance of making each fungicide application count – when growers get a chance to get back in the field – is even more critical. For effective fungicide application, beside selection of a good fungicide program, attaining optimum coverage for contact type fungicides on and within the canopy is very important for good disease control. While the proper selection of every spray parameter for effective fungicide application in one way or the other is equally important, there are few that are among the top of the list and have the most effect on both spray coverage and canopy penetration. Additionally, in some cases these parameters can easily be overlooked if a grower is already behind the spray schedule and in a rush to get in and out of his fields within the narrow spray window.

1. Spray Volume: One of the most effective ways to improve spray coverage and canopy penetration is using enough spray volume. Figure 1 below shows spray coverage obtained at three different locations (top, middle and bottom) in the peanut canopy for fungicide applied at the rates of 10, 15 and 20 GPA. As observed, the higher spray volume not only increased the coverage at the top of the canopy but also helped improve the coverage at the middle and bottom of the canopy due to more volume penetrating through and into the peanut canopy. While most pesticide labels have a minimum spray volume requirement (mostly 15 GPA for ground applied fungicides) to attain adequate coverage, and increased volume can further help improve coverage, it is critical that growers do not reduce the spray volume below the minimum recommended volume as it can significantly affect both fungicide coverage and efficacy. 

Figure 1. Illustration of spray coverage at three different spray volumes in the canopy.

2. Droplet Size: Size of spray droplets is also another important consideration for maximizing the effectiveness of fungicide application as it can influence both coverage and canopy penetration. Figure 2 below shows spray coverage obtained at three locations (top, middle and bottom) in the peanut canopy for same fungicide volume (15 GPA) applied at three different droplet sizes. Again, it is clearly visible that smaller droplets provided better coverage and canopy penetration while the larger droplets, especially ultra coarse, were unable to penetrate the peanut canopy resulting in considerably low coverage at the middle and bottom of the canopy. Since only some fungicide labels list droplet size requirements, it is important that growers utilize a combination of nozzle type and pressure that produces medium to coarse droplets to maximize the product efficacy. Growers who prefer to use auxin/dicamba nozzles for spraying peanut fungicides should be extra careful considering the influence of reduced coverage and canopy penetration with larger droplets.

Figure 2. Illustration of droplet size effect on spray coverage in the canopy.