Chemical pinching for roots of container plants

lations sometimes develop. Such variations are apparently the result of predators and parasites, climatic differences, varying tree conditions such as tree vigor and the plant growth cycle, all o€ which affect the feeding mites. The effects of temperature and humidity were the only considerations in the study reported here. Climatological conditions were found to vary from grove to grove and from locality to 1.ocality. The microclimate affecting individual mites might, even if the parasite-predator complex were not a factor, explain mite population differences that occur from place to place. Numcrous attempts at gathering information on the relationship of temperature and humidity to populations under field conditions were abandoned after two seaPons because of the difficulty in studying this small mite in various citrus groves where different irrigation, pest control and other cultiiral practices were used. Yuma spider mites have not been found near Phoenix, Arizona, nor in some areas in California where their presencr could be expected since environmental conditions there a re similar to thoTe of areas where this mite is prevalent. Laboratory tests showed that certain predacious mites and thrips, often found on citrus, prey on the Yuma spider mite, and in some areas may prevent their popnlations from increasing. Populations of the Yuma spider mite near Yuma, Arizona, and in portions of the Coachella and Imperial Valleys may exist because of the ahsenre of predators and parasites, hut the principal reason for the mites' choice of habitat area is probably temperature and humidity conditions.