Key Points
- Common rust is a leaf disease of maize that generally appears from mid to late December. Yield loss from rust is caused by reduced green leaf area. Here we assess the effectiveness of Amistar® (1L/ha) applied at different crop growth stages and levels of rust infection.
- Two trials were run during the 2008-09 season. The Hamilton trial had two sowing times while the Pukekohe trial had three. The sowing times were used to create different crop growth stages at the time of rust infection.
- Five treatments were applied to each site/sowing time combination: Control (no treatment) and Amistar applied as preventative, at disease onset, and at 3% and 6% leaf area infection.
- Results show that of the five site/sowing time combinations:
- Later sown crops had more disease pressure than earlier sown crops.
- The preventative and onset applications were generally better at reducing % of leaf area infected with rust.
- The reduction in rust infection translated into yield gains at only one site (Hamilton, 3 November sowing).
- The effectiveness of fungicide application appears to decline after 2 months.