32 BULLETIN 1474, U. S. DEPARTMENT OF AGRICULTURE 
melanose infection took place, the new growth came out and hardened 
commercially free of the disease and the later flushes did not develop 
melanose. On the contrary, those parts of the grove pruned during 
late spring had an abundance of melanose on the spring flushes and 
little or none on the growths that developed after pruning. Those 
parts of the grove pruned in late summer or early fall naturally were 
about as much injured by melanose as the unpruned groves. 
COST OF PRUNING 
The cost of pruning depends largely upon the thoroughness of the 
job, but it is commercially impracticable to attempt to remove all of 
the small twigs, fruit stems, etc., and it is these parts that are fertile 
sources of infection. The writers have records of some young bear- 
ing groves primed under contract for 20 cents a tree. In large 
bearing trees under normal conditions of vigor the cost is more 
because of the slowness of the work. Many growers estimate 
thorough pruning to cost 50 to 75 cents a tree, depending upon the 
season of the year and the prevailing cost of labor. Pruning as 
usually done is a slow, tedious, and costly operation and seems to be 
an unsatisfactory and ineffective means of preventing melanose out- 
breaks in average groves in Florida. 
PRUNING INEFFECTIVE 
Summed up, the attempt to control melanose by pruning out all 
deadwood, the source of infection, has generally proved ineffective 
and excessively expensive except where trees required severe cutting 
back or deheading. 
DUSTING FOR MELANOSE CONTROL 
Within the last few years the application of fungicides in the 
form of very fine dust has attracted considerable attention from 
owners of large acreages. This method of applying fungicides is a 
rapid one, so much so that two men and a tractor or a fast- walking 
team can easily dust 40 acres of grove in a day. Little or no more 
time is required for dusting a grove of large trees than for a similar 
acreage of small ones. Because of the one great practical advantage 
of dusting over spraying — namely, speed — considerable dusting has 
been done in Florida citrus groves within the last few years. Many 
observations have been made in commercially dusted groves for com- 
parison with results obtained from dusts applied experimentally by 
the Bureau of Plant Industry for melanose control. 
In 1922 a block of seedling orange trees was dusted very thorough- 
ly twice for melanose control. The first application was made April 
29, before infection had taken place, and the second on May 22. 
Both Bordeaux dust containing 12 per cent metallic copper and 
15-85 copper-lime dust were used. The following year (1923) 20-80 
copper-lime dust was used as well as sulphur dusts. Again the trees 
were dusted with great thoroughness and in time to control melanose. 
In 1924 six plots in the same grove were dusted from one to three 
times in late April and early May, well in advance of much melanose 
infection. The results of dusting experiments for melanose control 
in 1922, 1923, and 1924 are given in Table 6. 
