Occurrence, Cause And Control Of Longan Witches' Broom In Guangdong

A longan (Dimocarpus longan Lour.) disease with symptoms similar to witches' broom in Fujian and Guangxi Provinces, was also observed in the suburbs of Guangzhou, capital of Guangdong Province, for decades. Surveys and observation on spikelets and twigs affected, plus electron microscopy, grafting experiments, mite inoculation, pruning of affected spikelets and twigs, as well as integrated control trials demonstrated that witches' broom was caused by a mite, Eriophyes dimocarpi Kuang, and not by a virus or a twig borer. Integrated control trials were conducted on orchards with a total area of 13 ha during May, 1995 through August, 1998. Witches' broom-affected spikelets and twigs were pruned off and buds sprayed with a miticide (40% omethoate 1:1000 dilution, 50% colloid sulphur 1:400 dilution mixed with 20% dicofol 1:800 dilution). These measures reduced witches' broom incidence from 71, 96 and 73% to 12, 3 and 11% respectively by 1997.