Bulletin 229, Diseases of Citrus in Florida


and prevalence of stem-end rot in Florida appears to be increased
by periods of unusually warm weather after the fruit begins to
mature. Observations in the field, holding tests, and data from
market reports indicates that the Diplodia type of stem-end rot
is the most frequent type occurring both early and late in the
season, when the weather is fairly warm, and that the Phomop-
sis type is the most frequent one occurring during the inter-
mediate portion of the shipping season, when the weather is
cooler. In general, however, it may be stated that the greatest
development of stem-end rot occurs after the fruit of any par-
ticular variety has attained maturity. The greatest loss, as a
rule, occurs under conditions of shade and high atmospheric
humidity, although an abundance of scale-insects and the occur-
rence of drought near the time of maturity may also expedite
its development.
 A variety of organisms have been found to occur on or within
 the tissues of the stem button. Stem-end rot appears to result
 directly from the development of the causal organisms into the
 tissues of the fruit through the tissues of the stem button, al-
 though the same decays may also gain entrance at other points
 through wounds. Fawcett demonstrated in 1910 that uninjured
 citrus fruits can develop stem-end rot when the cut surface of
 the stem-end was inoculated with a pure culture of Phomopsis
 citri, even when the stems were left as long as three inches.
 CONTROL OF STEM-END ROT
 Since the occurrence and development of stem-end rot is in-
 fluenced by so many factors, it can readily be seen that its con-
 trol is a complex proposition for which many people, including
 the grower, packer, carrier, dealer, and consumer share the
 responsibility. The following different lines of control are rec-
 ommended.
 1. Removal of Dead Wood:-Pruning the trees of dead wood,
 by itself, cannot be depended upon as a practical means of con-
 trolling stem-end rot, at least not where the Phomopsis type pre-
 vails, but, if carefully done before May 1, it may materially re-
 duce Diplodia rot. The cost of securing this reduction, however,
 would be excessive in comparison with that of other control
 measures, if the expense of dead wood removal were chargeable
 to this item alone. The work of Winston, Fulton, and Bowman
 has shown that, while commercial pruning decreased the amount