Little information is available concerning spread of apple mosaic in the field. However, a number of workers in different countries have reported an increase in incidence of this disease in established orchards (Bennett, 1928amp;#x003B; Louw, 1944amp;#x003B; Anonymous, 1954amp;#x003B; Mulder, 1955). Blodgctt (1938), working in New York State, U.S.A., recorded the number of infected trees in a group of orchards over a tenamp;#x2013;year period and showed that there was a slow but significant increase in incidence of apple mosaic. Likewise records of infection in a Nova Scotia orchard, under normal orchard practice, showed a 50amp;#x0025; increase over a sevenamp;#x2013;year period (Anonymous, 1948), while in England, records in three blocks of trees over a fiveamp;#x2013;year period demonstrated a similar increase (Luckwill and Crowdy, 1950).
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