Abstract
Water-stress in young apple trees potted in sandy soil caused a six-fold retardation in Panonychus ulmi (Koch) population growth during two generations in a greenhouse. A considerably smaller retardation effect on the population growth occurred on water-stress trees growing in a compost-sand soil mixture. The leaves from moist compost-sand soil trees contained nearly the same percentage of nitrogen as those from water-stress trees, thus it is believed the detrimental effect of water-stress is caused by the inability of the mites to secure sufficient food supplies for maximum reproduction and growth.
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