Application of fusarium control fungicides requires specialized nozzles or nozzle combinations to achieve optimum results. Maximizing wheat head coverage requires both proper timing and the best nozzle configurations.
Maximize Spray Coverage of Wheat Heads
The key to applying fungicides to prevent fusarium head blight (FHB) is to spray all sides of all wheat heads with product. Heads that are missed or only partially sprayed are not protected adequately. Research carried out at the University of Guelph’s Ridgetown Campus since 2001 has evaluated spray nozzles and nozzle combinations to maximize spray coverage on all sides of the wheat heads.
Figure 4-5. Recommended Nozzle Orientation of a Forward-and-Back Double Nozzle Assembly. Nozzles with a shallow attack angle, such as forward-and-back double nozzles and alternating turbo floodjets, have significantly better spray coverage of wheat heads than nozzles spraying straight down.
Results showed that the closer the nozzles sprayed to horizontal, in a forward and back manner, the better the spray coverage.
Nozzles that spray close to vertical had significantly less spray coverage on the heads. Figure 4-5, Recommended Nozzle Orientation of a Forward-and-Back Double Nozzle Assembly, shows a boom-end view of the recommended nozzle orientation of a forward-and-back double nozzle assembly. Turbo FloodJet nozzles alternating forward and back every 20 in. along the boom also have this 15°-below-horizontal spray inclination. These two nozzle set-ups provide the best spray coverage for FHB control.
Follow label directions. More water should improve spray coverage, especially in windier conditions. For ground application keep water volumes in the 18-20 gallons/acre (GPA) range. Do not exceed 20 GPA application rates.
Spray coverage levels are very near equal from 10-20 km/h. In research trials, travel speed did not change the ranking or coverage level of the different nozzles. Spraying speed is not a critical factor in spray coverage of wheat heads.
Forward-and-back double nozzle assemblies and alternating Turbo FloodJets should be operated at 25-30 cm (10-12 in.) above the wheat canopy. Operate other nozzles a sufficient height above the canopy – about 50 cm (20 in.) – to allow full pattern development. Operating nozzles higher than this minimum nozzle-to-target distance will result in a significant reduction in spray coverage. Operating the boom at double the minimum nozzle-to-target distance from the wheat heads could reduce head coverage by as much as 50%.
Application Timing for Fungicides for FHB Control
Day 0 occurs when 75% of the heads on the main stems are fully emerged. Target spray applications for Day 1 to Day 4, with optimum timing of Day 2.
Current FHB fungicides (Folicur and Proline) are both rainfast in 1 hour. Spray once wheat heads are fairly dry. Moisture droplets on the heads may cause spray to run off, thereby reducing coverage levels.
Sprayer Cleanout Before Spraying Wheat
It is essential to clean out sprayers totally, including boom end caps. Wheat at heading is incredibly sensitive to any tank contamination, with yield loss approaching 100% in severe cases. If sprayer cleanout is not adequate, growers would be better not to spray for FHB.
Weather INnovations Inc (WIN) offers the DONcast forecast modelling system. This free service has been made possible by sponsorship from the Ontario Wheat Producers’ Marketing Board and Bayer CropScience. Visit the WIN website and follow the prompts.