Pre-harvest desiccation of rapeseed crop may allow a more timely harvest as well as increase the speed
and harvest operation efficiency as a second crop after rice. An effective desiccant which could be used as
a harvest-aid with no negative effects on rapeseed yield and quality would be advantageous for oil seed
crop producers and may reduce yield losses with no interferential effects on rice cultivation. Field
experiment s were carried out in a split plot design at Rice Research Institute of Iran (RRII) in the 2004-
2005 cropping season. Paraquat was applied to Hyola308, Hyola401, Hyola420 and RGS003 rapeseed
cultivars as main plots at the rates of 0.2, 0.4, 0.8 lit. based on 20% ai.ha-1 and a non-treated plot (sub-plot)
was used as a control. Paraquat treatments were applied based on grain moisture content of 40% to one
third of bottom siliques of inflorescence on the main stem in late April to late May. Results showed that
the effect of paraquat application was significant on grain moisture reduction rate, grain yield and oil
content. Paraquat at 0.8 lit.ha-1 promoted daily grain moisture reduction (2.94% day-1) compared to the
control (1.75% day-1) and harvest time (5-7 days earlier than control) with no adverse effects on grain yield
and oil content. Grain yield of treated plants were the same or higher than the control. The highest grain
yield was obtained with 0.4 lit.ha-1 paraquat (2370 kg.ha-1 in Hyola420 vs. the control; 2159 kg.ha-1). Results
also showed that paraquat application had no adverse effect on oil content and fatty acids profile. Oileic
acid content in Hyola308 at 0.2, 0.4 and 0.8 lit.ha-1 of paraquat and the control were 64.93, 64.22, 64.25 and
65%, respectively. Mean residues of paraquat in the grains for the medium to low application rates were
5.62 and 2.61 mg.kg-1, respectively and all of its rates were lower than the toxicity threshold. It can be
concluded that paraquat in reduced doses, can be used as a proper desiccant in rapeseed cultivation
