Robert E. Thomas
Information Specialist
573-882-2480
ThomasR@missouri.edu
Jan. 31, 2005
Soybean producers should be prepared to set
sprayers to fight Asian rust with fungicides
“Fungicides are rarely applied to soybean crops, but Asian rust has a tendency to hit wide and hard,” said Bill Casady. “A successful cure relies on timeliness.”
Asian soybean rust has been detected in nine states, including Missouri. When left untreated, the disease has caused up to 80 percent yield loss in infected soybean fields in South America.
Unlike other foliar soybean diseases, which can be managed through crop rotation and residue management, soybean rust survives only on living soybean plant material. Producers must be vigilant when scouting during the growing season.
The extent of the threat to Missouri soybean crops is still unknown. Casady said producers should understand how to set up sprayers to properly apply fungicides deep into the canopy where Asian rust is most likely to thrive.
Fungicides should not be tank-mixed with glyphosate for weed control in order to save a trip across the field, he said. The target for fungicides is the soybean plant, while the target for glyphosate is the weed population. It’s also unlikely that the windows for each type of application will coincide for that to become a suitable practice, he said.
“The maximum rates of the carrier as described on the label should be followed to achieve maximum efficacy. Research suggests that fungicides should be applied in a solution at a rate of no less than 15 gallons of spray mixture per acre,” he said.
Should fungicide spraying becomes necessary, most sprayers will need different spray tips than those that produce droplets in the 330 to 450 microns currently used to apply herbicides, he said.
Best fungicide efficacy will be achieved by applying medium droplet sizes of approximately 200 to 250 microns deep into the canopy. Tip selection and position will need to be based on the design characteristics of particular spray rigs.
“Calibrations should be performed early this spring to ensure that producers are ready to hit the ground running,” he said.
Research indicates that electrostatic sprayers, while excellent for spraying many types of vegetables and other valuable truck crops, have not proven effective for application of fungicides in a soybean canopy.
Aerial application may be preferred over ground application so that equipment will not have to enter the field. This eliminates tire tracks that can permanently damage soybean at a relatively late stage of growth, he said.
“Worse yet, the fields may be wet during the short window of application necessary for control causing severe compaction and ruts that may later complicate harvest,” he said.
“Although we can’t be certain, relying on ground sprayers may also increase the risk of spreading the disease from field to field,” he said.
Calibration procedures are available on-line in MU Publication G1270, Calibrating Field Sprayers. Go to http://muextension.missouri.edu/xplor/ and type G1270 in the search line.
Soybeans are the number one cash crop in Missouri with just over 4.6 million acres grown in 2004.
Source: Bill Casady (573) 882-2731
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