Influence of harvest date and hybrid on the mycotoxin content of maize (Zea mays) grain grown in New Zealand

Abstract

The changes in concentrations of the Fusarium mycotoxins nivalenol (NIV), deoxynivalenol (DON), and zearalenone (ZEN) in harvested maize (Zea mays) grain with time of harvest were determined, as well as how those changes were affected by the hybrid grown. The study used five hybrids in commercial use, three of these resistant to mycotoxin accumulation under New Zealand growth conditions (3902, 3787, 3394) and two less resistant (3751, 3514). The trial was conducted at five well‐maintained long‐term maize research sites over the three major maize‐growing regions of New Zealand. Results showed that apart from seasonal effects, hybrid choice was the major factor affecting the incidence and concentration of mycotoxins in harvested maize grain. Susceptible hybrids were significantly more likely to contain mycotoxins and to have high concentrations. It was determined that harvest date also had an impact on mycotoxin concentrations, with the best indicators of increased mycotoxin risk being either a prolonged time elapsed since the crop first reached 28% kernel moisture, or a very late (late June or July) harvest. The possibility of a site effect was also observed. At one site in the Waikato region, cob and kernel moisture contents were determined over most of the season, and the collected grain measured for infection by Fusarium species, and for contamination by mycotoxins. This showed that once the kernel moisture content fell below 30%, a substantial increase in Fusarium infection is likely. When this occurs, further delays in harvest can compromise grain quality and lead to increased mycotoxin contamination. The level of fungal infection and mycotoxin contamination would have been markedly less if the crops had been harvested earlier than they were, with the most susceptible hybrids being most affected. The study showed that although there may exist a reasonably wide harvest window for resistant hybrids planted at good sites, with more susceptible hybrids it is imperative to harvest as soon as practical, but that even then, mycotoxin contamination can be present.