The effects of four levels of mite-days, an estimate of mite feeding damage, on almond tree growth and yield were investigated to obtain data necessary for the determination of spray thresholds. The current year's almond growth or yield was not significantly influenced by spider mite infestations. However, significant reductions in development, growth, and yield were observed one season after an infestation. Terminal shoot extension and mean leaf size were significantly reduced by 300 and 424 mite-days, respectively (P<0.05). Similarly, the increase in yield from 1979 through 1980 was significantly reduced by 424 mite-days. This reduction appeared to be the result of reduced fruit set (P<0.05), whereas floral initiation was not significantly affected.