Florida Agricultural Experiment Station


able situations will be further handicapped by the effects of
the adverse factors of site that may stimulate greater disease
development. The growth and development of the citrus tree is
largely influenced by the conditions of its environment. These
may be such as to promote a good to average development of the
trees or they may be such as to produce weak and non-produc-
tive trees or trees that are subject to various injuries and set-
backs from time to time. However, it is not intended to give
the impression that only weakened or injured trees are sub-
ject to attack by diseases, since there are a number of diseases,
such as melanose, scab and canker, that are capable of attacking
the most vigorous and healthy trees. On the other hand, there
are other diseases, such as withertip, that attack only weakened
or injured trees. These diseases are often unable to attack the
vigorously growing tissues but, if a part becomes weakened or
injured, they may greatly expedite the decline of the tree. A
healthy, vigorous tree will have a much greater resistance to
many diseases than one of low vitality, especially when subject
to devitalizing influences periodically.
 Among the factors of site that affect the general health and
productivity of the grove may be mentioned soils poorly adapted
to the growth of citrus trees, especially when closely underlaid
by rock, hardpan, or marl, and situations where the trees are
subject to extreme fluctuations of soil moisture or injury from
cold or high winds. In selecting land for the grove, it is highly
important that these factors be considered with regard
to the probable effect they may have on the future welfare of the
grove. Fortunately, some of the adverse factors of site may
be modified to decided advantage even after the grove is es-
tablished. The introduction of drainage, irrigation, frost pro-
tection, wind-breaks, cover-cropping, and changed methods of
cultivation and fertilization, where such are desirable, frequently
will contribute greatly to the general improvement of the grove
condition. It is often difficult and costly, however, to overcome
the bad effects of unfavorable environmental conditions after
the grove has been established.
 GENERAL CARE
 Widely differing methods are employed in cultural practices
 and fertilization, each often giving successful results. This is
 not strange, however, when we consider the different soil types,