Some seasons in New Zealand, conditions are unfavourable for fire blight development and yet streptomycin is still applied by growers as a preventative measure. If we could predict when a fire blight infection event is likely to occur, we could then decide whether streptomycin is required or not. Computer models, which predict fire blight infections based on weather data, have been developed in the United States and are now being trialed in New Zealand. To date results look promising under New Zealand conditions. Infection by any disease requires a susceptible host, disease inoculum and the correct environmental conditions.
Flowers open with stigmas and petals intact.
Growers can install a weather station to measure maximum and minimum temperature and rainfall, or use information from an automatic weather datalogger. However, the computation of heat units required for infection and the occurrence of disease symptoms can be complicated. This is why dedicated computer-based systems are so useful. Computer printouts give the daily temperatures, wetness and likelihood of infection which can be interpreted to decide whether a streptomycin spray is required. In 1992, work was also started on a computer based prediction system specifically designed for the New Zealand pipfruit industry.