THE HALL SCALE ERADICATION PROJECT 1 
The program specified that three annual fumigations of each property 
should be given after the last live scales had been seen, and intervening 
spring and summer oil sprays as a supplementary treatment. The only 
exception was in the first test block of 800 trees. No oil sprays were made 
after this block had been fumigated, because of the possibility that they 
might decrease the chance of finding survivors, and only two fumiga- 
tions were made after the last live scales had been found. Intensive 
inspection for 3 years since the last fumigation has not shown any scales. 
They were probably eradicated in this block with a somewhat weaker 
program than elsewhere. 
By the spring of 1952 the treatment program had been completed on 
properties containing about 22,000 hosts, and about 2,800 hosts at Davis 
had been removed by the University of California. Properties containing 
about 4,600 hosts in the Bidwell Park and Pershall areas, representing 
infestations found during 1950, 1951, and 1952, were still under treatment. 
The known infestations 1n 1952 were limited to these areas. 
After treatment was discontinued, properties were placed on an inspection 
basis for annual checks for surviving scales. Thus far, no live scales have 
been found on any properties after the fumigation program has been 
completed. 
SUMMARY 
The Hall scale CNélotaspis hallz (Green)) was first discovered in the 
United States at Chico, Calif., in 1934. In the United States it has been 
found only in California, in Chico, and in 2 localities within 100 miles of 
that city. 
Since an attempt to eradicate the scale after its first discovery was un- 
successful, a more comprehensive eradication project was organized in 1941, 
with the U. S. Bureau of Entomology and Plant Quarantine and the 
California Department of Agriculture cooperating. 
Plants found infested in California are limited to the geneta Prunus and 
Amygdalus and the shrub Spireae veitchiz. Additional hosts reported from 
other countries include Pyrus, Malus, Cydonia vulgaris, and Cerasus.  Pre- 
ferred hosts include almond, peach, plum, nectarine, and prune. Scales 
infest all parts of the hosts and cause conspicuous blotches on some fruit. 
The first crawlers emerge late in March or early in April, but emergence 
continues until about the middle of October. There is at least a partial 
second generation in the summer. Only females are found during the 
winter months. 
Inspection showed infestations at Oroville and Davis, and at five separate 
areas neat Chico. Infested properties contained about 29,000 host plants. 
Infestations in the different areas Were probably established by movements 
of infested host material. Spread within the areas appears to have been 
by wind and other agencies, such as birds and insects. 
Oil sprays reduced the scale population but did not eradicate it. A 
method of fumigation with hydrocyanic acid gas in gastight tents over the 
plants was developed. Trees were fumigated with 40 cc. of liquid hydro- 
cyanic acid per 100 cubic feet for 50 minutes in the daytime in the dormant 
season. The gas was introduced with a blower applicator and most of it 
was evacuated with a large blower before the tents were removed. Tents 
made of plastic-covered cloth were transferred from tree to tree with 
especially designed pullers. 
