Citrus problem areas

The latest development in the field of citrus pests involves nematodes. The citrus nematode (Tylenchulus semipenetrans Cobb) has been known for many years in California, Florida, and Argentina and probably exists in most other areas. Whether it could do much damage to healthy citrus trees is a moot point. In recent years, however, more and more workers in California have been inclined to blame it for poor tree condition and their inability to replant citrus with citrus satisfactorily. The idea that nematodes are of importance has been stimulated by the finding in Florida that the cause of spreading decline is the burrowing nematode, Radopholus similis (Cobb) Thorne. This nematode, hitherto unknown as a citrus pest, destroys the feeder roots particularly below a depth of about 2 feet and has been found to a depth of 14 feet. In the course of this work a number of other nematodes, hitherto unreported on citrus, have been found and at least some of these appear to damage citrus roots. The indications are that nematodes are going to be one of the real citrus problems of the future. 

In areas where particular crops are grown continuously, decreases in production with time have been noted. The condition is usually species speciAc, and the disorders which result are frequently referred to as soil-sickness or replant problems. Fruit trees are especially sensitive and the problem has been encountered with apples, peaches, grapes, cherries, plums, and citrus. In most situations, phytotoxicity has been related to the formation of toxic materials as a consequence of the microbial decomposition of plant remains. 

Red scale is a problem in many of the drier banana growing areas. The damage is occasioned by injury to leaves, but the most noticeable damage is in the yellow spotting of the green fruit where the scale has been attached. So far the only control for red scale has been oil emulsion sprays similar to those used in the citrus industry. Highly toxic insecticides, such as used on citrus, cannot be used on bananas because the fruit is harvested almost every day. 

This discussion covers the field only briefly. Numerous diseases and insects have been omitted which are tied more to certain areas. That the problems are important is attested by the fact that citrus production is the largest world-wide fruit-producing industry, while in the United States it exceeds the total of apples, pears, and peaches combined. As citrus is grown so extensively in so many areas where organized research is lacking, technical information is of paramount importance. 

It is both encouraging and exciting to observe that the field of immunology has finally been directed toward plants and molecules of plant origin. For all of plant science, the future developments of the RIA, EIA and other immunoassays should aid greatly in solving some of our most troublesome problems. We are of the opinion that the immunoassay has the potential to become a major analytical tool in the citrus industry and in Table IV are listed just some of the areas where this procedure might be employed. 

The problems of the dairy and citrus fruit industries are typical of those encountered with products produced in different areas of the country or at different times of the year. 

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