Florida Agricultural Experiment Station


is known concerning the different disease manifestations caused
by this widespread fungus. The effect of Diplodia in causing
an important fruit decay, however, is well known and will be
discussed in connection with stem-end rot.
 SYMPTOMS OF DIPLODIA DIEBACK
 Attacks of Diplodia on citrus
 trees may manifest themselves
 in a number of different ways.
 Probably the most common form
 of attack is a rapid dying back
 of the twigs and small 1er
 branches which closely r e-
 sembles withertip. In fact, this
 trouble is often called withertip
 and can be distinguished only by
 laboratory examination. T h e
 twigs may die back from the tips
 for some distance, ending at a
 sharply defined line which de-
 marks the diseased from the
 healthy tissue. In such cases
 the point at which the progress
 of the disease becomes arrested
 usually is characterized by a
 slight exudation of gum. In
 other cases no limiting line is
 developed and the entire twig
 and possibly part of a larger
 branch may be involved and kill-
 ed (Fig. 44). Under favorable
 moisture conditions, the bark
 that has been killed eventually
 becomes dotted by numerous
 minute, black pustules which are
 the fruiting bodies of the fun-
 gus. Instances have been noted
 from time to time, especially on
 lemon a n d grapefruit trees,
 where the fungus follows the at-
 Fig. 44.-Diplodia dieback on lem- tacked twig and infects a fruit
 on branch, showing exudation
 of gum at base of lesion, borne on it, the decaying fruit