Benzaldehyde as a soil fumigant, and an apparatus for rapid fumigant evaluation

An apparatus was developed for the rapid and facile evaluation of soil fumi gants in a controlled manner using small volumes of soil, The apparatus con sisted of a manifold to which were attached six canisters containing a loam y sand soil (adjusted to -100 kPa soil water potential). The soil was infes ted with either conidia of Fusarium oxysporum or Trichoderma harzianum; scl erotia of Sclerotinia minor; ascospores of Talaromyces flavus; vermiculite colonized with Pythium aphanidermatum; or beet (Beta vulgaris L., cv, Detro it Red) seed colonized with Rhizoctonia solani, Using nitrogen gas (N-2) as a carrier gas, either N-2 or N(2)plus benzaldehyde was passed continuously through the soil for 24, 48, or 72 hours. At all three exposure times, ben zaldehyde + N-2 reduced viability of R. solani and S. minor, and reduced po pulations of P. aphanidermatum and T. harzianum. Populations of F. oxysporu m were reduced after 48 and 72 hours of exposure to benzaldehyde, whereas p opulations of T. flavus were reduced only after 72 hours of exposure. Fumig ation with benzaldehyde + N-2 for 24 hours did not affect soil pH 1 week af ter exposure, but fumigation for 48 or 72 hours temporarily lowered pH from an average of 6.86 to 5.57 and 5.32, respectively. The biocontrol fungus, T. flavus, was less sensitive to benzaldehyde than the pathogens or the bio control fungus, T. harzianum, Thus, combining T. flavus with benzaldehyde t o enhance biocontrol may be possible.