Robust Barley Response to Silwet X-77 Adjuvant Rate in 5.2 and 19.2 GPA Spray Volume with AMS 21619 Fungicide  

S. Halley,Langdon Research Extension Center-North Dakota State University, Box 310 Hwy 5 E Langdon, North Dakota 58249

*Corresponding author PH: (701) 256-2582, E-mail: shalley@ndsuext.nodak.edu  

OBJECTIVES  

To determine if efficacy of fungicide, AMS21619 (Bayer experimental), can be enhanced by differing rates of Silwet X-77 adjuvant at 5.2 or 19.2 gpa spray volume to Robust Barley.  

Introduction  

Barley producers in traditional barley producing areas have been frustrated by the inconsistent performance of fungicides applied to barley. As a result barley acreage has shifted to different regions of the state where diseases have not been as prevalent. However, diseases are developing in these regions and disease levels increasing when environmental conditions are appropriate.  

Barley is particularly difficult to research because obtaining adequate disease levels for effective fungicide evaluation has been inconsistent. The extended period of heading among barley main stem and tillers, lack of yield loss due to FHB, and an inability to distinguish losses between leaf diseases and FHB, and near zero tolerance for the presence of the toxin deoxynivalenol (DON) by the malting industry complicate prioritization of research goals.  

Adjuvants are recommended additions to some fungicide solutions to improve consistency of performance. Often recommendations are for additions based on volume for volume relative to the tanks solution (1 pt/ 100 gallons of tank solution). Fungicide applicators are recommended to use water volumes greater than most herbicide application volumes. Wide range of volumes is used, as low as 3 gpa with aerial application to 20 gpa, ground application on small grains. The variability in solution volume means total adjuvant amounts applied can vary widely depending on application choices. One class is the organosilicates. This particular class, specifically Silwet L-77, reduces the tension of the spray droplet. Too much adjuvant will move the fungicide off target and directly to the soil negating the benefit of the fungicide.   

MATERIALS AND METHODS  

The barley cultivar Robust was planted for fungicide evaluation in a field at the Langdon Research Extension Center in spring 2002. An area was planted with a Melroe double-disk grain drill, disks spaced 6-inches apart. The area was divided to plots 12 ft. wide by 20 ft. long in a RCB design with six replicates arranged as a Silwet X-77 Rate x GPA factorial. Recommended production practices for Northeast North Dakota were followed. Three weeks prior to heading a Fusarium spawn grown on spring wheat was hand broadcast at a rate of approximately 200 grams/plot.  

Silwet X-77 rates were:

      1.      Untreated
2.      0
3.      1.5 ml/acre.
4.      4.8 ml/acre
5.      23 ml/acre
6.      46 ml/acre  

Treatments were applied by a modified SPRAYAIR� tractor sprayer. The sprayer was modified to distribute the solution from orifices angled 30 degrees downward from horizontal oriented forward and backward to maximize spike coverage. The solution carrier was CO₂ delivering volumes of 5.2 and 19.2 gpa into the air stream. The tractor traveled on the left half of the plot area. This area also provided border to reduce off target drift between treatment areas. Visual estimation FHB incidence and field severity, 20 samples per plot, (spikelet count per individual head multiplied times FHB infected spikes per head) were determined 20 days after fungicide application. Each plot was harvested with a Hege plot combine and the grain sample cleaned and processed for yield, test weight, and plump measurement. Data was analyzed with SAS GLM.  

RESULTS AND DISCUSSION  

FHB field severity was reduced by fungicide application but there were not differences between adjuvant rates and fungicide with no adjuvant. All fungicide treatments increased test weight over the check. Silwet L-77 at 1.5 ml/acre also had greater test weights than no adjuvant and 46 ml/acre adjuvant. Test weight was also increased when gpa was 19.2.  

At the 5.2 gpa application volume yield was increased when the adjuvant rate was 46 ml/acre giving an 11.3 bu yield increase over the untreated. At 19.2 gpa yields were decrease at the 23 and 46 ml/acre rates compared to no adjuvant and the 1.5 ml/acre adjuvant rate. Most recommendations for adjuvant are based on a % of the tank volume. This trial would tend to indicate that increased application volume requires decreasing adjuvant amounts.  

Summary  

There were no differences in FHB field severity among Silwet X-77 rates. The addition of Silwet X-77 at 1.5 or 23 ml/acre increase test weight over no Silwet X-77, 46 ml/acre and the untreated. Greater water volume also increased test weight. Yield was increased by using greatest rates of adjuvant at low water volume but decreased when rates of 23 and 46 ml/acre were used with greater water volume.    

Table 1. FHB disease, yield, test weight, and plump response to Silwet X-77 rate with AMS 21619 fungicide application to Robust Barley Langdon, 2002.

GPA	Silwet L-77	FHB		Yield	Test	Plump
	Rate	Incidence	Severity		Weight
	ml/acre	%	%	bu/acre	lb/bu	%
GPA*Silwet L-77 Rates
5.2	0	76.7	11.2	80.5	46.8	87.7
	1.5	67.5	9.8	76.2	47.3	88.4
	4.8	80.0	11.3	75.7	47.4	88.7
	23	76.7	9.9	76.0	47.1	89.1
	46	71.7	10.9	91.3	47.4	89.1
	Untreated	83.3	13.7	80.0	46.4	87.7
19.2	0	75.8	11.3	86.1	47.5	90.3
	1.5	74.2	9.8	86.6	48.2	89.5
	4.8	80.8	11.1	82.2	47.4	88.3
	23	70.0	10.8	76.8	48.1	89.2
	46	75.0	8.0	75.3	47.0	86.1
	Untreated	85.6	20.3	82.1	46.7	87.1
Silwet L-77 Rates averaged over GPA
	0	76.3	11.3	83.3	47.2	89.0
	1.5	70.8	9.8	81.4	47.8	89.0
	4.8	80.4	11.2	79.0	47.4	88.5
	23	73.3	10.4	76.4	47.6	89.1
	46	73.3	9.5	83.3	47.2	87.6
	Untreated	84.2	17.0	81.0	46.6	87.4
GPA averaged Silwet L-77 Rates
5.2		76.0	11.1	79.9	47.1	88.4
19.2		76.8	11.9	81.5	47.5	88.4
Silwet Rate*		NS	3.3	NS	0.6	NS
GPA*		NS	NS	NS	0.4	NS
Sil*GPA		NS	NS	7.3**	NS	NS
%CV		15	35	12	2	4

*Significant at 0.05 probability level for mean comparisons.

** Significant at 0.1 probability level for mean comparisons.  

Figure 1. Yield response to Silwet X-77 rate with AMS 21619 fungicide at 5.2 and 19.2 gpa water volume applied to Robust Barley Langdon, 2002.