2.1.2. Visual Disease Ratings

Visual disease ratings were performed weekly from calendar week 17–23. One plot was rated two times at the same locations where hyperspectral measurements took place. Disease incidence was assessed by the eye of a human rater. The diseased leaf area (%) was rated on 15 leaves per leaf level. Additionally, the growing stage and the visible leaf area of each leaf level in the hyperspectral image (from top view) was ascertained.

**Figure 1.** Field trial layout (RGB stitch from unmanned aerial vehicle (UAV) images) at the research station Campus Klein-Altendorf (Rheinbach, Germany) of winter wheat varieties Bussard and Asano in 2018, with treatment declaration and measurement strategy. The trial was designed in two long rows of plots to reduce the number of turns and keep continuous measurements.

#### 2.1.3. Crop Stand and Disease Development

The vegetation in 2018 started late in March and was denoted by a drought that especially affected the length of the growing season and led to an early harvest in July (Figure 2). *Septoria tritici* blotch, tan spot, and powdery mildew were insignificant throughout the growing season. YR could establish a significant infection on cultivar Asano, and measurements were not aggravated due to mixed infections. The first YR symptoms were found in mid of April and were based on natural infection incidences. Until the beginning of May (BBCH 31), a serious increase of YR was rated. Warm days and cold nights seemed to favor infection incidences through dew formation. Until the middle of May (BBCH 37-39), YR was the dominating disease.

**Figure 2.** Schematic overview of the course of the 2018 vegetation period. For each calendar week, the actions are presented and disease occurrence of yellow rust (YR) is shown. Weekly assessments and measurements were performed during the vegetation period (CW = calendar week; BBCH = growing stage).
