Chemical defoliation of hevea by thermal fogging

Abstract

Chemical defoliation of rubber Hevea spp. planting, done about a month before the annual wintering, as a means of avoiding leaf diseases, has attracted considerable interest in the South of Bahia in the control of Microcyclus ulei and Phytophthora spp. Though ideally defoliants are applied by aerial spraying, the recent trend has been to substitute holicopters with fogging machines for treating mature rubber. Two field trials were carried out in 1981 with Tridiazuron, a defoliation of very low mammalian toxicity, fogging an emulsion concentrate with Leco 120-B in one, and with Tifa Tart in the other. The results were contrasting in the two sites: While satisfactory defoliation resulted in the first site, the treatment had no effect in the other. In the former an earlier and more uniform refoliation helped the trees to largely escape outbreaks of both M. ulei and Phytophthora spp. The differential effect obtained may be attributed to weak and different degrees of fog formation in the two sites. This preliminary work shows, nevertheless, that low toxicity defoliants can be fogged when aircraft is not available.