Management of Allium white rot [Sclerotium cepivorum] in onions on organic soil with soil-applied diallyl disulfide and di-N-propyl disulfide
The efficacy of two sclerotia germination stimulants, diallyl disulfide (DADS, 85.5%; related compounds, 4.5%) and di-N-propyl disulfide (DPDS, 88%; related compounds, 2%) were evaluated in naturally infested field plots and in the greenhouse for reduction in populations of sclerotia and control of onion white rot in organic soil. Field trials evaluated one or two applications of DADS or DPDS injected into soil at 10 L/ha in 500 L/ha of water. To determine the treatment effects on the survival of sclerotia, sacs of 100 sclerotia were exposed to treated and untreated soil in the field and greenhouse. In controlled greenhouse studies, survival of sclerotia was significantly decreased when sclerotia were exposed for 1 to 3 months to soil treated with DADS or DPDS compared with untreated soil. DADS was considerably more effective than DPDS. In field trials, survival of sclerotia decreased after 3 months exposure to DADS-treated soil. Single DADS applications reduced disease incidence on onions at harvest compared with the untreated checks at three of four sites. Following two DADS applications, disease was reduced to below 1% at all four sites. DADS applied to organic soil provided effective control of white rot under conditions of moderate disease pressure.