The peach silver mite (PSM),Aculus cornutus(Banks), was monitored on leaves of peach,Prunus persicaL. Batsch, ‘Flordaking’ and ‘June Gold’, from 6 May to 5 August 1985. PSM first appeared in significant numbers on 21 May on unsprayed trees, peaked on 11 June, and disappeared by 8 July. Between 50 and 3,400 peach silver mite-d (PSMD) per leaf accumulated per tree. Percentage of leaf damage varied between 0 and 88% of the adaxial leaf surface. Net CO2assimilation rate (A), leaf conductance (gl), and transpiration (E) were inversely related to PSMD and percentage leaf damage. Predicted reductions inAat 3,000 PSMD and 80% leaf damage were ca. 20 and 22%, respectively. More PSM occurred on ‘June Gold’ than ‘Flordaking’ but interactions between PSMD and cultivar or percentage leaf damage and cultivar were not significant forA, gl, E, or chlorophyll concentration. The percentage of decline inglwas similar to the decline inAand leaf chlorophyll concentration was not affected by PSM. These data suggest that PSM is primarily an epidermal feeder, and that PSM feeding may inhibit leaf gas exchange by affecting stomatal function. PSM were at least 10-fold less debilitating to leaf gas exchange of peach thanTetranychus urticaeKoch in a previous study, and may not ordinarily need to be controlled by chemical sprays.