STUDIES ON THE BIOLOGY OF BLACK MOLD (ASPERGILLUS-NIGER) ON TEMPERATE AND TROPICAL ONIONS .2. THE EFFECT OF TREATMENTS ON THE CONTROL OF SEED-BORNE ASPERGILLUS-NIGER

Treatment of A. niger-inoculated onion seed with benomyl dust (1 g a.i./kg), or a foliar spray of thiram (0.4% a.i./ha) applied to plants grown from inoculated seed under temperate (UK) conditions reduced the incidence of A. niger in harvested crops. Treatment of naturally contaminated Sudanese onion seed with a benomyl + thiram mixture at a rate of 2.5 + 2.5 ga.i./kg or soaking the seed in hot water (15 min at 60 degrees C) reduced the incidence of black mould on bulbs grown in the Sudan in field soil that had not previously been used for onion production. The seed treatments were less effective in crops produced in fields regularly used for onion production. However, incubation of harvested bulbs in moist chambers showed that damage to the internal storage tissue of onion bulbs caused by A. niger was reduced by seed treatment.