*3.2. Correlations between Di*ff*erent Mycotoxins*

A heat map with correlations between different mycotoxins for 2016–2018 is shown in Figure 3. NIV was significantly correlated with DON (r = 0.38, *p* < 0.001) and its derivates 3-ADON (r = 0.22, *p* < 0.001) and 15-ADON (r = 0.28, *p* < 0.001). NIV was also significantly correlated with ZEN and ENN B, although the correlations were rather weak (r = 0.21, *p* < 0.001 and r = 0.12, *p* = 0.0496, resp.). Other correlations were non-existent or not significant. When splitting the data per year, similar results were obtained, however some differences occurred (Figures A1–A3). For instance, the correlation between NIV and DON was the strongest in 2017 (r = 0.65, *p* < 0.001), but was not significant in 2016 and 2018 (r = 0.08, *p* = 0.455 and r = 0.21, *p* = 0.058, resp.). Furthermore, ZEN and ENN B were significantly correlated in 2016 and 2017 (r = 0.35, *p* < 0.001 and r = 0.37, *p* < 0.001, resp.). FUMs were not correlated with any other mycotoxin in any year, except with 15-ADON in 2018 (r = 0.31, *p* = 0.004).

**Figure 3.** Heat map based on the pairwise Pearson correlation coefficients between the measured mycotoxin concentrations from 2016–2018. A darker blue color indicates a stronger negative correlation, a darker red color indicates a stronger positive correlation. Significant correlations are indicated with asterisks (\* *p* < 0.05, \*\*\* *p* < 0.01). DON+ = the sum of the concentrations of DON, 3-ADON and 15-ADON. FUM = the sum of the concentrations of FB1, FB2 and FB3.

### *3.3. Fusarium spp. DNA in Maize Samples in 2017-2018*

Incidence of *F. graminearum*, *F. verticillioides*, *F. culmorum* and *Fusarium* spp. in maize samples in 2017, 2018 and both years combined, is shown in Figure 4; Complete results per sample can be found in supplementary Table S1. In 2017, every maize sample was contaminated with at least one *Fusarium* sp., while in 2018, 36% of the samples were free of *Fusarium* spp. DNA. In both years, *F. verticillioides* was

detected most often, with a prevalence of 99% in 2017 and 54% in 2018. *F. graminearum* and *F. culmorum* were detected in 90% and 85% of the maize samples in 2017, and 43% and 51% in 2018, resp.

**Figure 4.** Incidence of *F. graminearum*, *F. verticillioides*, *F. culmorum* and *Fusarium* spp. in general, in samples of harvested maize in 2017, 2018 and in both years combined.

### *3.4. Correlations between Mycotoxin Concentrations and Fusarium spp. DNA*

Using qPCR analysis, we could calculate correlations between mycotoxin concentrations and *Fusarium* spp. DNA on maize fields, and interspecies correlations between *Fusarium* species (Figure 5). Rather weak but significant correlations were found between the amount of *F. graminearum* DNA and *F. culmorum* DNA (r = 0.21, *p* = 0.009) and *F. verticillioides* DNA and *F. culmorum* DNA (r = 0.19, *p* = 0.024). A strong significant correlation was found between DON+ and *F. graminearum* DNA (r = 0.53, *p* < 0.001). Both *F. graminearum* and *F. culmorum* were significantly correlated with higher concentrations of NIV (r = 0.35, *p* < 0.001 and r = 0.36, *p* < 0.001, resp.). Furthermore, *F. verticillioides* DNA was positively correlated with FUM (r = 0.20, *p* < 0.016), but an even stronger correlation was found between FUM and *F. graminearum* (r = 0.27, *p* < 0.001). However, the latter correlation is based primarily on one data point with a high concentration of FUM and a high *F. graminearum* DNA content. When removed from the dataset, the resulting correlation is no longer significant (r = −0.03, *p* = 0.707). Similarly, when removing two outliers from the dataset with a very high FUM content, the correlation between *F. verticillioides* DNA and FUM becomes more profound (r = 0.45, *p* < 0.001). Lastly, when eliminating one outlier from the *F. culmorum* and *F. verticillioides* data, the correlation becomes non-existent (r = −0.06, *p* = 0.482) (See Figure A4). Other correlations were less dependent upon outliers. Splitting the data per year yields similar results as the combined data (Figures A5 and A6).

**Figure 5.** Heat map based on the pairwise Pearson correlation coefficients between measured mycotoxin concentrations and DNA of *F. graminearum*, *F. verticillioides* and *F. culmorum* from 2017–2018. A darker blue color indicates a stronger negative correlation, a darker red color indicates a stronger positive correlation. Significant correlations are indicated with asterisks (\* *p* < 0.05, \*\*\* *p* < 0.01). DON+ = the sum of the concentrations of DON, 3-ADON and 15-ADON. FUM = the sum of the concentrations of FB1, FB2 and FB3.
