Bulletin 140, Dieback of Citrus Trees


to grow in the upper layers of soil. Cultivation should be re-
duced to a minimum and the trees be heavily mulched.
 Where the hardpan consists of layers of clay or of rock or
marl, it should be broken with dynamite to give the roots plenty
of loose soil in which to grow. Care must be taken that there is
no lack of drainage. Where possible, normal cultivation should
 be given; where not, the trees should
 be heavily mulched to hold the soil
 moisture. The cover crop can be cut
 and left on the ground to rot, or be
 worked into the soil with a cut-away
 Sharrow. Purely mineral fertilizers
 ^i with the average ammonia content
 l may be used at regular intervals, care
 being taken not to overfeed the trees.
 Excessive Cultivation.-When die-
 back is brought on by the excessive
 cultivation of pineland, flatwoods or
 interior hammock land, cultivation
 should be reduced as much as possible.
 The grove should not be plowed for a
 year or more. The cut-away harrow
 may be used instead when it is neces-
 sary to break up the sod. The Acme
 harrow should be used only where it
 is necessary to conserve the soil mois-
 ture. The cover crop can be cut, and
 worked into the soil with the cut-away
 harrow. Mineral fertilizers with a low
 ammonia content should be used for
 one or two applications, if the grove
 has been well fed previously.
 FIG. 13.-Maltiple buds Any considerable amount of stirring
 of the soil in groves located on the shell
 lands, or lands where the coquina rock occurs near the surface,
 may be favorable to dieback. When it occurs in trees on such
 soils cultivation should not be practiced. The trees should be
 mulched and the grass and weeds cut and left on the ground.
 Irregular Moisture Conditions in the Soil.-Irregular mois-
 ture conditions that may lead to a development of dieback may
 occur in either the high or low soils. The disease is more likely
 to develop under such conditions where the trees have been well