S CIRCULAR 920, U. S. DEPT. OF AGRICULTURE 
about 15 acres were infested. A great deal of host material had been shipped 
from Davis to growers throughout the State, but no infested plants origi- 
nating from this infestation were found outside the Davis orchard and 
nursery. No scales were found in the University’s orchard at Winters, 
although much material was interchanged between Davis and Winters. 
All the infestations appear to have originated from movements of infested 
host material from the Plant Garden and all except the Davis infestation 
probably date back to 1930 or before. 
Two types of spread within the infested area are illustrated in figure 5. 
In the Johnson area (fig. 5, 4) the infestation probably originated with the 
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Ficure 5.—Maps of infested areas: A, Johnson; B, Bidwell Park. Infested properties are shown 
in black; noninfested host plantings with hatching. Probable origin of the infestation is 
shown by cross in white circle. 
SCALE IN FEET ‘ A 
250’ 
planting of an infested nectarine tree from the Plant Garden in 1927, before 
the presence of the scale was known. The infestation was heavy in parts 
of this orchard when it was discovered and was placed under a spray pro- 
gram in 1941. The spread was limited to contiguous properties. Wind 
was the chief, perhaps the only, agent of spread. In all but one of the 
other infested areas the spread was of this type. 
In the Bidwell Park area (fig. 5, B) the infestation probably started on a 
property on which a great deal of material from the Plant Garden was 
planted before 1929. This and other properties were heavily infested when 
the scale was discovered on them in 1949. In the meantime the scale had 
spread to other orchards without becoming established on many properties 
nearer to the source of infestation. Birds and insects, as well as wind, may 
have been responsible for some scattering of infestation in this area. 
