Bulletin 140, Dieback of Citrus Trees


applications, after which the normal amount of ammonia should
be used. Ammonia starvation is not necessary in all cases of
dieback. In cases other than those brought on by overfeeding,
it may be harmful. In such cases the normal amount of ammonia
should be used.
 The ammonia in fertilizers used on trees where dieback has
been brought on by overfeeding, or where
dieback occurs on soils well supplied with
humus and moisture, should be derived en-
tirely from mineral sources; in the other
case it should be largely from mineral
sources.
 In the case of dieback on dry sandy soils
of the high pine and the spruce pinelands,
where it has not been brought on by over-
feeding, the use of stable manure in limited
amounts has in a number of cases proved
helpful in curing the disease. The writer is
unable to explain why, in certain cases, ma-
nure can induce the disease, whereas under
other conditions it appears to be helpful in
curing it. It is probably on account of the
effect which it has upon the organisms in
the soil.
 Cultivation and Cover Crops.-The stop-
ping of cultivation is a helpful practice where
the disease occurs under certain conditions. FIG. 11 -Bark ex-
 crescences on fruit
 The normal system for the cultivation of spurs
 lands, where cultivation is possible, is to
 plow the grove either in the fall or the early spring, and to main-
 tain a dust mulch during the spring months until the rainy
 season begins, by the use of the Acme harrow over the whole
 grove every ten days or two weeks. The grove is then laid by
 for the summer and a crop of grass and weeds, or of legumes, is
 allowed to cover the ground. In late summer this is cut. In
 some cases it is removed for hay, in others it is allowed to lie
 until fall when it is plowed under; or an early cutting may be
 made and removed for hay, and a second growth made to be cut
 and turned under. In a bearing grove the plow is run shallow,
 not to exceed six inches. In young groves the plowing may be
 deep in the middles but shallow near the trees.
 In cultivated groves affected with dieback the system should