Ground Application of Fungicide for the Suppression of Fusarium Head Blight in Small Grains

Vern Hofman, Retired Extension Agricultural Engineer, North Dakota State University, Fargo
Scott Halley, Crop Protection Scientist, North Dakota State University, Langdon Research Extension Center, Langdon, N.D.
Gary Van Ee, Agricultural Engineer, Biosystems and Agricultural Engineering, Michigan State University, East Lansing
Marty Draper, Plant Science Department, South Dakota State University, Brookings
Marcia McMullen, Extension Plant Pathologist, North Dakota State University, Fargo
Charla Hollingsworth, Extension Plant Pathologist, University of Minnesota, Crookston

Introduction

Fusarium head blight (FHB) has caused considerable income loss for wheat and barley growers in the past decade. Estimates of crop loss to growers in North Dakota, South Dakota and Minnesota are significant. Serious yield and quality losses from FHB occur whenever wet weather coincides with the heading and flowering stages of the crop. One of the management strategies to control FHB is to use fungicides, but traditional methods of fungicide application for leaf disease control have proven ineffective for control of this disease. In FHB, the flowering grain head (wheat) or fully emerged grain head (barley) is the site of infection of the Fusarium fungus. If fungicides are applied with nozzles that direct the spray vertically or nearly vertically, most of the fungicide is deposited on the leaves or ground and misses the targeted grain head. The most effective FHB control occurs when fungicide is applied to protect all sides of the grain head. The challenge is to find the most effective and efficient ground application techniques to achieve maximum fungicide deposition and efficacy for FHB control.

Early Studies and Recommendations

Early NDSU studies indicated fungicide deposition on the grain head was most effective if the spray was directed at a nearly horizontal angle both forward and backward to the direction of travel with flat-fan (FF) nozzles mounted 8 to 10 inches above the heads. Most of these studies were conducted with backpack-type application equipment traveling at speeds less than 4 miles per hour. Also, early studies using a fluorescent tracer dye showed that increasing spray volumes increased dye coverage on the grain head. As a result of these studies, recommendations for ground application of fungicides for FHB control included using forward/backward nozzle configurations delivering up to 20 gallons per acre (gpa).

Recommended Fungicide Application Techniques for FHB Suppression in
Small Grains with Ground Applicators

Produce a fine- to medium-sized drop (300 to 350 microns) with a flat-fan nozzle.
Angle all (flat-fan) nozzles forward 30 to 45 degrees down from horizontal. Thirty degrees down is preferred over 45 degrees.
Apply fungicide at 10 gallons per acre for controlling FHB.
Position spray nozzles 8 to 10 inches above the grain heads.

Recent Studies

Nozzle orientation

Recent studies with ground application equipment using flat-fan nozzles traveling at speeds of 6 mph or faster have shown that the increased travel speed reduces the effectiveness of the backward-facing nozzle. The faster speed reduces the velocity of the backward-directed droplets, causing them to move almost vertically downward.

The forward motion of the vehicle at speeds of 6 mph or greater improves fungicide deposition on the head with a single forward-facing FF nozzle. Studies also found that gentle breezes (for example, 3 to 8 mph) will cause fine spray drops to deposit on the upwind side of the head, causing a reduced amount of spray on the downwind side of the head. These studies showed that a single, forward-facing FF nozzle, angled 30 to 45 degrees from the horizontal (30 degrees preferred), provided equal or sometimes even slightly better spray deposition and disease control, compared with the combination of forward- and backward-facing nozzles. This spray configuration also can be obtained with an air-assist spray system by angling the air orifices forward. The air-assist air stream changes the vertical orientation of the grain head by pushing the grain heads forward so they are nearly perpendicular to the air stream.

Droplet size

North Dakota State University studies using ground application equipment traveling at speeds of 6 mph or greater have found that a large fine to a small medium-sized drop (300 to 350 microns) provides more consistent control than very fine (less than 200 microns) or coarse (larger than 400 microns) spray drops. The 300 to 350 micron-sized droplets are sufficiently fine for even distribution on grain heads and sufficiently large to resist drift or movement away from the grain head. Also, the 300- to 350-micron droplet has shown the most consistent results of moving past the awns and depositing on the grain spikelets.

Water volume

The NDSU research also has shown that equal or better control of FHB or efficacy was achieved at volumes of 10 gpa with a single set of flat-fan nozzles directing the spray forward at 30 to 45 degrees from the horizontal. While the coverage with a 10-gpa application is less than a 20-gpa volume, the actual quantity of fungicide measured on the grain head increases because the concentration of fungicide in the 10-gpa volume is double the concentration in a 20-gpa volume.

Based on the results of the most recent studies, NDSU provides the following recommendations to reduce application cost, improve efficiency as less water is needed in the field and reduce damage to nozzles (angle extensions are smaller in size) when they drag in the crop.

Adapting Spray Applicators to Recommendations

Some spray booms are not easily modified to direct the spray pattern forward at the recommended 30 degrees down from the horizontal. But, most spray equipment suppliers will be able to supply a nozzle body adapter, 45-degree nozzle cap or single-swivel nozzle adapter (Figures 1, 2 and 3) that can produce the recommended forward angle of the spray pattern. They are available with quick-disconnect nozzle caps so nozzles can be changed or cleaned easily.

The American Society of Agricultural and Biological Engineers has developed a spray drop size classification system. It places spray drops into one of six drop size classifications. They range from very fine (less than 180 microns) to extremely coarse (greater than 655 microns). More information about the drop size classification system can be found in publication FS-919, “Choosing Drift Reducing Nozzles.” The publication is available at North Dakota county Extension Service offices or on the NDSU Web site at www.ext.nodak.edu/extpubs/ageng/machine/fs919w.htm.

Spray drop size is determined by nozzle type, orifice size and operating pressure. The information for a fine to medium drop size is available from all nozzle manufacturers. They have charts that indicate the drop size each of their nozzles produces at a particular pressure. Applicators will need to select a nozzle to give the desired drop size at the desired application rate, travel speed and operating pressure. For example, if an application of 10 gpa is desired at 12 mph, a flat-fan nozzle with an 80-degree spray angle discharging 0.3 gallon per minute would need to operate at nearly 60 pounds per square inch (psi). This combination produces a fine- to medium-sized drop. A nozzle with a 110-degree discharge angle would need to operate at only 40 psi, but a nozzle discharging 0.4 gallon per minute would be needed. A 110-degree FF nozzle produces a smaller droplet than an 80-degree nozzle when operated at the same pressure. The previous two examples are for sprayers with a 20-inch nozzle spacing.

Different nozzle manufacturers may have slightly different drop size classifications for their nozzles. Follow their recommendations to produce a fine- to medium- (300 to 350 micron) sized drop.

References

Halley, S., G.Van Ee, V. Hofman. 2005. “Effect of Nozzles on Fungicide Efficacy for Control of Fusarium Head Blight.” Pages 194 to 197. U.S. Wheat and Barley Scab Initiative, Michigan State Univ., East Lansing, Mich.

Van Ee, G., S. Halley and V. Hofman. 2004. “Significant Accomplishments and Future Endeavors in Chemical Application.” Page 378. U.S. Wheat and Barley Scab Initiative, Michigan State Univ., East Lansing, Mich.

Hooker, D.C., H. Spieser and A.W. Schaafsma. 2004. “Effective Application of Fungicides on Wheat Heads: What’s the Best?” Page 330. U.S. Wheat and Barley Scab Initiative, Michigan State Univ., East Lansing, Mich.

Halley, S., G. Van Ee, V. Hofman, S. Panigrahi and D. Gu. 2004. “Effect of Application Technology Parameters on Spray Volume and Drop Size on Fungicide Efficacy for Control of Fusarium Head Blight.” Pages 306 to 310. U.S. Wheat and Barley Scab Initiative, Michigan State Univ., East Lansing, Mich.

Halley, S., G. Van Ee, V. Hofman, S. Panigrahi and H. Gu. 2003. “Ground Spray Systems and Spray Parameter Evaluation for Control of Fusarium Head Blight on a Field Scale Basis.” Pages 69 to 75. U.S. Wheat and Barley Scab Initiative, Michigan State University, East Lansing, Mich.

McKay, K., V. Hofman, M. McMullen and K. Michels. 2003. Comparison of Aerial Application With Ground Application of Folicur Fungicide for the Control of Fusarium Head Blight in Durum Wheat.” 2003. Page 94. U.S. Wheat and Barley Scab Initiative, Michigan State University, East Lansing, Mich.