Florida Agricultural Experiment Station


recting exanthema probably will not be demonstrated until more
is known concerning the nature of this disease. It is evident,
however, that copper sulphate is beneficial to citrus trees when
absorbed in small quantities, regardless of whether through
the leaves or roots, or as injections into the trunk.
 Spraying with Bordeaux Mixture:-It has also been known in
 Florida for many years that bordeaux mixture, sprayed upon
 the foliage of affected trees, is a very effective cure for exan-
 thema. Froscher, of Brevard County, first brought this remedy
 to the attention of the Florida State Horticultural Society in
 1898. When there are indications of the fruit becoming ammoni-
 ated, or there is reason to believe from the past behavior of the
 grove that the fruit may become ammoniated, spraying the
 trees with bordeaux mixture will save the particular crop of
 fruit developing and prove an aid in correcting the trouble on
 the trees themselves. Applications of bordeaux mixture, of
 course, unless combined with oil emulsion or followed by an ef-
 ficient oil emulsion spray, are likely to induce a marked increase
 in the development of scale and certain other insects, since this
 fungicide kills off the beneficial fungi which commonly hold in-
 sects in check. To be most effective in the control of exanthema,
 the bordeaux mixture should be applied just prior to the flush
 of growth that may be affected by the disease. Hence, the spray-
 ing should be done in late winter, late spring or late summer.
 MOTTLE-LEAF OR FRENCHING
 Mottle-leaf, or frenching as this trouble is frequently termed
in Florida, is a condition of partial chlorosis that is of wide-
spread occurrence throughout the citrus region of Florida and
appears to be present in varying degrees in all countries where
citrus trees are grown.
 Chlorosis is a general term applied to that condition of plants
in which the normally green parts either fail to develop, or lose
after they have developed, the green color characteristic of them
and become yellowish-green to yellow or almost white. Any-
thing which prevents or retards the formation of the green pig-
ment (chlorophyll) normally occurring in plants interferes with
their normal functioning, affects directly the carbohydrate food
supply and results in a weakened, diseased condition. A number
of different types of chlorosis of citrus occur in Florida, of which
mottle-leaf is by far the most important.