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Experts Recommend Fungicide Application for Scab Suppression

Wet weather across North Dakota could cause a scab (Fusarium head blight) problem for wheat and barley producers.

Editors: This is a corrected version of the story to reflect 250- to 300-microns instead of 200- to 300-microns.

By John Nowatzki, Ag Machine Systems Specialist

NDSU Extension Service

The wet weather across North Dakota could cause a scab (Fusarium head blight) problem for wheat and barley producers. The heavy rains have produced wet soils, which could produce excellent conditions for the growth and spread of the fungus that causes scab. Serious yield and quality losses from scab occur whenever wet weather coincides with the heading and flowering of wheat and barley.

Recommendations from recent North Dakota State University research for ground application of fungicides to control scab in small grains are to direct the spray as perpendicular to the grain head as possible with 250- to 300-micron drop sizes. These recommendations are available in the NDSU publication AE-1314, ""Ground Application of Fungicide for the Suppression of Fusarium Head Blight in Small Grains."" It is available on the Web at http://www.ag.ndsu.edu/pubs/plantsci/pests/ae1327.htm.

This 250- to 300-micron size of drop is considered a ""large fine to a small medium drop size."" Nozzle manufacturers use the drop size classification system developed by the American Society of Agricultural and Biological Engineers. The classification system uses six categories of drop sizes, which range from very fine to extremely coarse.

The best application method is to use a flat-fan nozzle pointed 45 to 60 degrees forward from vertical and 10 gallons of water per acre. The 10-gallon-per-acre rate performed equal to or better than 20 gallons per acre, compared with other application methods. NDSU research found that covering one side of the grain head is sufficient to suppress scab infestation levels. However, it is important to recognize that applying fungicides only will reduce the level of scab and will not control all the scab.

Spray nozzle adapters are available from spray equipment suppliers to convert nozzle bodies to direct the spray pattern forward at the recommended angle. They are designed to fasten to quick-connect nozzle bodies. Use flat fan nozzles that produce 250- to 300- micron droplet sizes and apply at 10 gallons per acre. The nozzle discharge angle should be 80 degrees and mounted about 8 to 10 inches above the grain heads.

The large fine to a small medium drop size produced better results than smaller drops that tend to attach to grain awns. Larger drops provided poorer coverage. The 250- to 300-micron drop sizes penetrate the awns best, while also providing good head coverage. The best suppression of the disease occurred with single, forward-facing nozzles, even though the backside of the head received only a small amount of fungicide because one side of the head was covered well with the fungicide that provided local systemic activity.

Trials using ""twin orifice"" nozzles produced only moderate control, and only slightly better than a single nozzle pointed straight down. This nozzle directs the two spray patterns in a more vertical direction, so the sides of the heads receive only minor amounts of the fungicide. Twin nozzles that direct the spray pattern in a more horizontal direction are not available.

Nozzle designs that use two forward and backward directed nozzles worked well with 4 mph travel speeds. But, as travel speeds were increased to around 8 mph, the rear-facing nozzle produced little to cover the backside of the head. The faster travel speed counteracts the rearward-facing spray pattern and the spray drops fall almost vertically from the nozzle, avoiding contact with the sides of the heads.

NDSU Agriculture Communication

Source:John Nowatzki, (701) 231-8231, john.nowatzki@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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