Abstract
The occurrence of the broad mite, Polyphagotarsonemus latus (BANKS), was observed first in the fall crop of potatoes at several places in Nagasaki in 1975. The mites were supposed to migrate from other host plants adjacent to potato fields. The propagation of mites on the potato variety, Shimabara, was poorer than on the varieties, Dejima and Tachibana. A greenhouse experiment indicated that the growth of mite population was proportional to the initial number of mites placed on the potatoes, 2, 5 and 10 mites per plant, up to 25 days. However, the number of mites including adults and nymphs per first small leaf reached about 150 in all plots 30 days after the initial infestation, and soon after the mites completely withered up the potatoes. Spraying of chinomethionat (Morestan) WP at the rate of 750g AI/ha gave a satisfactory control of mites in pot and field experiments, but acephate (Ortran) WP was ineffective.
