Whenever the conversation turns to Asian soybean rust, the topic of fungicide application is guaranteed to come up. Certainly it was a key topic for several speakers at the 2006 National Soybean Rust Symposium held Nov. 29-Dec.1, 2006 in St. Louis, MO, which had nearly 320 attendees.
One of those speakers was Bob Wolf, Extension specialist in application technology at Kansas State University (KSU), during a session on fungicide application strategies for soybean rust management.
Learning What Works
There are quite a few questions that retailers and their growers need to ask themselves before any fungicide application, Wolf told the audience. These questions include what fungicide or combination of fungicides to use and at what disease stage, will adjuvants be beneficial, and what application system would be best to use.
Another key question, said Wolf, is what spray nozzle type, orifice size, and pressure will be necessary for good coverage into the lower parts of the soybean canopy. Studies are ongoing at various universities, including at KSU by Wolf and his graduate research assistant, Naga Prasad Daggupati.
By comparing 20 nozzle types in the lab and then narrowing those to 12 in field trials for their ability to achieve the crucial lower canopy spray, Wolf and Daggupati hoped to determine which nozzles might be most effective for preventing or controlling the disease. Since the onset of soybean rust in the U.S., the most common recommendation from nozzle manufacturers and researchers has been to use twin or double nozzle configurations.
For the lab tests, the pair used a special spray track machine to simulate actual field spraying situations, including multiple treatments and replications. Water sensitive paper placed in the lower canopy collected the droplet patterns for analysis.
Results Favor Any Nozzle
The KSU results found that even though differences were minimal for most treatments, the data did not support the commonly accepted strategy to use twin or double nozzle configurations to improve the spray penetration into the lower canopy.
Dealerships may not need to outfit their spray systems with nozzles other than the conventional turbo and extended range nozzle types, Wolf said. For the field treatments, there were no significant differences in the 10 highest performing nozzles, 4 of which were twin or double orifice nozzle configurations. “These conventional nozzle systems performed well, provided the smaller orifice sizes and higher pressures were selected,” he said.
For further details from the session led by Wolf, along with the 43 other oral/67 poster presentations at the symposium, visit www.plantmanagementnetwork.org or www.rustready.com. Coordinated by the American Phytopathological Society in partnership with 22 related organizations, the symposium was led by Don Hershman, University of Kentucky, coordinator and Anne Dorrance, The Ohio State University and John Rupe, University of Arkansas, technical committee co-chairs.