20, 2 Lee and Shino: Citrus-canker Control Experiments 123 
in culture is about 5° C. according to Peltier,(5) the minimum 
temperature for infection and development of the disease upon 
calamondin (Citrus mitis) and grapefruit (Citrus maxima) 
is 20° C. This may be taken roughly as an index of the action 
on the Washington navel orange (Citrus sinensis) ; according to 
this, then, canker activity from November until the end of April 
is negligible or entirely absent. 
During this period also the rainfall is not heavy and the canker 
organism is not disseminated seriously. Although in May the 
rainfall is slightly increased and the temperatures are slightly 
higher, it may probably be classed with November to April, as 
a month of canker inactivity in Japan. The rainfall for the 
year is shown in Table 2. 
Table 2 shows a very decided increase in rainfall for June 
and early July. The Japanese in Nagasaki claim that there are 
twenty-one days of continuous rainfall always at this season, 
and the season is called the nyubei. Although the definite period 
of twenty-one days may be doubted, there is a period of from 
three to four weeks at this time when there is heavy and intense 
rainfall; this is accompanied by a very perceptible rise in temper- 
ature. After the nyubei, there is a period of little rainfall 
which, in usual years, constitutes almost a dry season. This 
lasts through July and early August, sometimes to the end of 
August. During August and September, however, typhoons 
sometimes are recorded and these, although irregular in occur- 
rence, must be prepared for. The rains accompanying typhoons 
raise the rainfall total for these months well above that for July 
and early August. After the September typhoons October is a 
comparatively dry and cool month. 
It was pointed out previously by the first mentioned of the 
present writers that canker dissemination is largely dependent 
upon free moisture, rain or dew, on the foliage. As previously 
mentioned, Peltier has shown that canker infection is dependent 
on temperature also, varying according to the host, but safely 
at 20° C. or above. With these factors, rainfall and temper- 
ature, in view, it is apparent that usually there are but two 
periods favorable to canker dissemination and infection in south- 
western Japan: (a) the period of the nyubei, which may begin 
any time in early June and extend into July, and (0b) the period 
when typhoons may occur, usually from the latter part of 
August until the end of September. The nyubei is a period of 
steady, drenching downpours, but with little or no strong wind. 
The period August and September is not always accompanied © 
