Table 5. Coefficients of correlation between spectral indices and grain yield at different growth stages of wheat infected by powdery mildew during two seasons.

spectral indices a	2009–2010				2010–2011
	10.5.3 b	10.5.4	11.1	Mean c	10.5.3	10.5.4	11.1	Mean
RED	−0.397	−0.395	−0.269	−0.394	−0.301	−0.192	−0.303	−0.341
NIR	0.789	0.533	0.739	0.765	0.712	0.551	0.705	0.805
DVI	0.804	0.564	0.728	0.766	0.713	0.557	0.709	0.805
RVI	0.688	0.527	0.549	0.661	0.553	0.460	0.611	0.644
NDVI	0.695	0.570	0.599	0.676	0.530	0.452	0.572	0.636
λ red	0.655	0.121	−0.112	0.406	0.656	0.288	−0.056	0.519
dr red	0.496	0.407	0.466	0.656	0.081	0.089	0.490	0.185
Σdr 680-760 nm	0.810	0.504	0.691	0.775	0.715	0.552	0.714	0.812

^aDVI = difference vegetation index, RVI = ratio vegetation index, NDVI = normalized difference vegetation index, .λ _red = red edge position, dr _red = red edge slope, Σdr _{680-760 nm} = the area of the red edge peak.

^bGrowth stage using Feekes scale.

^cCorrelation between yield and mean spectral reflectance indices across three growth stages.