Heat treatment of citrus for control of red scale. I. Trials on Washington Navel fruit in a dehydrator

Abstract

Heat treatments, ranging from 50 to 70°C and for varying durations, were carried out on freshly picked Washington Navel fruit infested with red scale. Counts of the living and dead scales were made 3 weeks after treatment. The time-mortality curves were approximately sigmoidal and similar to normal dosage-mortality curves. Reliable 100 per cent. "kills" were obtained for treatment periods ranging from 1 hr for the 70°C treatment to 2¼ hr for the 50°C treatment. However, the fruit damage effects of the 70°C treatment were severe and preceded the time required for 100 per cent. scale mortality, whereas with the 50°C treatment no fruit damage occurred until after this time and even then the damage was very slight. Raising the relative humidity of the treatment chamber from 12 to 40 per cent. in the 50°C treatment did not significantly alter the time required for either 50 per cent. or 100 per cent. scale mortality. It is considered that the killing of the scales was a temperature rather than a dehydration effect, and that it probably occurred at a fairly similar threshold lethal temperature for all temperature treatments used.