**5. Conclusions**

240 Fungicides for Plant and Animal Diseases

Net return (\$ ha-1)

Net return (\$ ha-1)

140

160

180

200

220

240

260

140

160

y = 296-4.9x; r<sup>2</sup>

and economic analyses conducted in 2009-2010 in Nebraska, USA.

**4.4.7 Relationship between yield increase and net return** 

y = -46 + 0.17x; r<sup>2</sup>

and economic analyses conducted in 2009-2010 in Nebraska, USA.

180

200

220

240

260

Disease severity (%) 14 16 18 20 22 24 26 28 30

Fig. 6. Relationship between disease severity and net return due to fungicide application in winter wheat cv. Millennium. Data were obtained from field experiments conducted in 2007

In 2007, there was a strong, positive linear relationship between yield increase and net return (Fig. 7). Eighty five percent of the variation in net return was explained by yield increase. Every unit (kg ha-1) of yield increase resulted in a net return of \$0.17 ha-1.

= 0.85, p = 0.0002

Yield increase (kg ha-1) 1000 1100 1200 1300 1400 1500 1600 1700

Fig. 7. Relationship between yield increase and net return due to fungicide application in winter wheat cv. Millennium. Data were obtained from field experiments conducted in 2007

= 0.32, p = 0.0658

We conclude that the fungicides Quilt, Headline, Tilt, Quadris, and Stratego effectively controlled foliar fungal diseases in winter wheat, resulting in yield increase and a profitable net return in 2007. Environment had a significant effect on yield increase and net return. In 2006 when dry conditions led to development of low levels of disease, yield increase and net return were very low. However, in 2007 when excessively wet weather favored development of high levels of disease, yield increase and net return were high. These results suggest that fungicide application to winter wheat can be profitable when environmental conditions favor development of damaging levels of disease. Timing of fungicide application at GS 39 generally resulted in a higher yield increase and a higher net return than a GS 31 timing. Therefore, under Nebraska conditions, when a farmer can afford only one spray in a growing season, spraying at GS 39 or later would likely be more beneficial than spraying earlier. Regression analysis of 2007 data showed an inverse linear relationship between yield increase and disease severity and between net return and disease severity, and a positive linear relationship between yield increase and net return, confirming the negative effect of disease on yield and suggesting a potential benefit from fungicide application to control foliar fungal diseases in winter wheat when environmental conditions favor the development of damaging levels of disease.
