The Influence of Cover Crop Cultivation on Populations of Injurious Insects and Mites in Florida Citrus Groves

Abstract

Cultural practices involving the natural ground cover or cover crop vary considerably from area to area and grove to grove in Florida. This variation is, in some instances, governed by the level of the water table or the type of soil involved. More frequently, however, cultivation is modified by the opinions of the grower. Some growers maintain weed-free groves by frequent disking, harrowing or chopping. Others permit cover crop development during the summer months but practice clean cultivation in the fall, winter and spring. Still others allow weeds and wild grasses to grow unhampered from one picking season to the next. Horticultural and agronomic reasons cited for such variations in practices include moisture conservation, soil conservation, fire protection, soil protection, tree stimulation and efficient grove management. Furthermore, many growers believe that such practices cause increases or decreases in insect and mite abundance. To date only two studies have been conducted on the influence of cover crop cultivation on insect and mite infestations. The first was an investigation by Osburn and Mathis (1944) concerning the citrus rust mite, Phyllocoptruta oleivora (Ashmead). These workers concluded that there was no difference between rust mite infestations on trees in clean cultivated plots and on trees grown in plots having a cover crop. They did, however, record stimulation of the trees in the clean cultivation plots. Two years later the same workers (Osburn and Mathis, 1946) reported markedly greater infestations of Florida red scale, Chrysomphalus aonidum (L.), on trees growing in cultivated plots than on trees in uncultivated plots. They were unable, however, to demonstrate striking differences in the percentages of parasitized scales or fungi-affected scales and concluded that tree stimulation, a result of cultivation, was the important factor in the development of larger scale infestations. The present study was conducted to obtain preliminary cultivation data on the major injurious insects and mites attacking Florida citrus and to correlate, if possible, any differences recorded with changes in the rates of parasitism or predation.