Blueberry 
Commercial blueberry culture is confined largely to special areas 
in Massachusetts, Michigan, New Jersey, and North Carolina. Blue~- 
berry plantings are affected by various diseases, but mummy berry, 
due to a fungus, and stunt, a virus disease, are the two major 
commercial problems. 
Mummy berry occurs in all the blueberry-growing areas. The young 
blossoms are infected, and the fruit is converted into a hard, 
inedible mass as the result of the development of the fungus in the 
inner tissues. Blighting of the twigs further reduces the size of 
the crop. Partial (about 75 percent) control is achieved by using 
caustic sprays to kill the fungus on the ground and by spraying the 
bushes with fungicides to prctect them from infection. Stunt occurs 
only in New Jersey and North Carolina. Infected plants slowly de- 
cline in vigor, become unproductive, and eventually die. Control 
megsures include use of disease-free nursery stock, roguing of 
diseased fields, and vector control by use of insecticides. 
Cherries, Sour 
The commercial production of sour cherries is seriously affected 
by two types of disease. The fungus disease leaf spot (Coccomyces) 
occurs in plantings east of the Rocky Mountains. It causes spots 
and a shot-hole effect on the leaves and excessive defoliation. It 
is present every year and requires a regular spray program of sulfur, 
copper, or organic material for its control. Sour cherry yellows, 
a virus disease, occurs wherever sour cherries are grown in the 
United States. The disease is manifest by a yellow-green mottling 
of the leaves followed by successive periods of defoliation. The 
trees are not killed, but the number of fruit-bearing spurs is re- 
duced each year. The only control is the preduction and use of 
certified disease-free nursery stock. 
Citrus 
Citrus trees and fruit are affected by a number of fungus diseases, 
which for the most part are kept under control without much effort. 
On the other hand, several virus diseases, especially tristeza and 
quick decline, which are very like each other and may be caused by 
the same virus or by strains of one virus, menace the very existence 
of the citrus industry. The virus diseases occur in Florida, along 
the Gulf coast, and in California, and it is estimated that 1,500,000 
trees ars killed every year. The trees gradually lose vigor and 
become less productive for several years prior to their death. The 
sour orange, long used for citrus rootstocks, is extremely susceptible 
to the causal virus or viruses, and control depends on the finding 
and use of satisfactory resistant rootstocks. 
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