A. Gamliel and J.J. Stapleton (1997) Phytoparasitica 25(Suppl.):31S-38S Improvement of Soil Solarization with Volatile Compounds Generated from Organic Amendments A. Gamliel 1 and J.J. Stapleton 2 Combining organic amendments with soil solarization is a nonchemical approach to improvement of the control of soilborne plant diseases. Pathogen control in solarized - amended soil is attributed to a combination of thermal killing and enhanced generation of biotoxic volatile compounds. Apparently, pathogen sensitivity to biotoxic volatile compounds is enhanced with an increase of soil temperature and acts in combination with antagonistic microbial activity. Enhanced biocontrol also may be involved with some amendments. Toxic volatile compounds including alcohols, aldehydes, sulfides, isothiocyanates, and others were detected in soil amended with cruciferous residues during heating. Field solarization of soil amended with composted chicken manure gave better control of pathogens and higher yield of lettuce and tomato than either treatment alone. KEY WORDS: Soil solarization; organic amendments; cabbage; plant residues; fumigation; soil disinfestation. INTRODUCTION Soilborne plant pathogens survive in the soil and cause extensive damage to many crops. The most common approach for their control is by elimination before or after planting, by means of destructive methods of soil disinfestation. This should be done in such a manner as to reach the pathogens in all physical and biological niches in the soil. Chemical fumigants have proved of great advantage to agricultural production for many years. They are strong eradicants by nature, resulting in simultaneous control of a variety of pests. However, negative effects, i.e., eradication of beneficial organisms, and a negative shift in the biological equilibrium in the soil, are also possible during their use. Unfortunately, certain fumigants were found to possess limiting negative attributes, such as acute and chronic health hazards, environmental pollution, and even potential atmospheric ozone depletion. The increased environmental concern due to these negative factors has been a major factor in triggering regulatory restriction on the use of soil fumigants. In many countries the use of fumigants, especially nematicides including 1,2- dibromochloropropane (DBCP), ethylene dibromide (EDB) and 1,3-dichloropropene, has been discontinued or suspended, and phase-out of methyl bromide, which is the most widely used soil fumigant, is currently underway. Few soil disinfestation chemicals are still available, leaving the farmer in many cases without effective means to combat soilborne pests. None of the available methods used to control soilborne diseases is effective against all pathogens (including those caused by nematodes and bacteria, which are difficult to control), or can be used in all instances. Thus, development of nonchemical methods for effective control of soilborne diseases is needed. 1 Laboratoryfor Research on Pest ManagementApplication, ARO,The VolcaniCenter, Bet Dagan 50250, Israel [Fax: +972-3-9604704; e-mail: agamliel@agri.huji.ac.il]. 2Statewide IPM Project, Universityof California, KearneyAgriculturalCenter, Parlier, CA 93648, USA. Phytoparasitica 25 :Suppl., 1997 31S