Leaf Injury and Defoliation Caused by the Citrus Rust Mite, Phyllocoptruta Oleivora

Abstract

The persistence of high populations of citrus rust mite in untreated Valencia orange groves from late October 1974 to early January 1975 combined with abnormally dry weather caused severe injury to both the spring and summer flushes of leaves. Seventy percent of the leaves had one or more types of rust mite injury of varying severity. Upper surface injury occurred on 43.7% of the leaves and was most prevalent on spring flush. Lower surface injury and mesophyll collapse occurred on 37.4 and 19.0% of the leaves, respectively, and were most prevalent on summer flush. Overall defoliation of both healthy and injured leaves was 9.5% being significantly greater on summer flush. Citrus rust mite injury to the lower leaf surface appeared to be associated with defoliation. The area of injured leaf surface in relation to leaf size appeared to have no effect on leaf abscission. The interaction between the various types of leaf injury associated with citrus rust mite and prolonged moisture stress in relation to defoliation is discussed.