Toxicity Evaluation Of New Fumigants And Research On The Application Technology

China is a large agricultural country, and agriculture is the basic industry of the national economy. Since the reform and opening up, the great achievements made in agriculture are largely attributed to the extension of protected cultivation technologies and applications in China. The successive planting of crops, however, lead to the increasing serious soil-borne problems, such as soil-borne disease and weeds, thus it is triggering a serious threat to the interests of farmers. Currently, the most direct and effective means to overcome soil-borne problems was soil chemical fumigation. Methyl bromide(MB), the most widely used and the best soil fumigant in the world, could effectively control soil-borne fungi, bacteria, nematodes, insects and weeds. However, scientists have found that MB is one of the significant ozone depleting substances(ODS). MB was, therefore, officially classified as a controlled substance by UNEP in November, 1992. In 2003, the Chinese government signed the Copenhagen Amendment to the "Montreal Protocol" and agreed to phase out MB by January 1st, 2015.Learn from foreign advanced technology and experience, we have carried out a lot of laboratory studies and field trials to find the proper MB chemical alternative and the relevant application technologies based on the domestic conditions in China. The main conclusions of the researches on evaluating the new chemical soil fumigants as effective alternative to MB are as follows.1. Conclusions of evaluating the new chemical soil fumigants in the laboratory studies(1) Research on the fumigant combinationsLaboratory studies found that seven fumigant combinations, dimethyl disulfide + dazomet(DMDS+DZ), dimethyl disulfide + metham sodium(DMDS+MS), 1,3-dichloropropene + metham sodium(1,3-D+MS), 1,3-dichloropropene + dimethyl disulfide(1,3-D+DMDS), chloropicrin + dazomet(Pic+DZ), chloropicrin + ally isothiocyanate(Pic+AITC), and dimethyl disulfide + ally isothiocyanate(DMDS+AITC), all exhibited positive effects on soil-borne nematode(Meloidogyne spp.), soil-borne fungi(Fusarium spp. and Phytophthora spp.) and common weed seeds(Abutilon theophrasti and Digitaria sanguinalis).(2) Research on single fumigantsLaboratory studies found that chloropicrin(Pic) and dazomet(DZ) can provide excellent controover R. solanacarum. The concentrations of Pic and DZ required to control 50%(EC50) of Rsolanacarum were 2.7 and 27.6 mg a.i. kg soil, respectively.2. Conclusions of evaluating the new chemical soil fumigants in greenhouse trials(1) Research on the fumigant combinations in cucumberGreenhouse trials revealed that four fumigant combinations, DMDS+DZ, DMDS+MS, 1,3-D+MS, and 1,3-D+DMDS, successfully controlled the infestation of Meloidogyne spp., reduced the number of Fusarium spp. and Phytophthora spp. in soil, and maintained high cucumber yields and income for farmers. All of the four fumigant combinations provided similar results to that of MB with respect to disease control, plant vigour, cucumber yield and income for farmers. The recommended alternativecombination and application methods were DMDS+DZ with soil mixture + chemigation(30+25 g a.i. /m2); DMDS+MS with chemigation(30+21 g a.i. /m2); 1,3-D+MS with chemigation(10+21 g a.i. /m2) and 1,3-D+DMDS with injection/chemigation(10+30 g a.i. /m2).(2) Research on the fumigant combinations in tomatoGreenhouse trials in tomato revealed that three fumigant combinations, DMDS+DZ, 1,3-D+DMDS, and 1,3-D+DZ, all significantly reduced the number of Meloidogyne spp. in soil, successfully suppressed the infestation of Fusarium spp. and Phytophthora spp., and gave high tomato yields and income for farmers. All of the three fumigant combinations did not displayed significant difference from MB with respect to disease control, plant vigour, tomato yield and income for farmers. The recommended alternative combinations and application methods were as follows: DMDS+DZ with soil mixture + injection/chemigation(40+25 g a.i. /m2); 1,3-D+DMDS with injection(10+40 g a.i. /m2); and 1,3-D+DZ with soil mixture + injection(10+25 g a.i. /m2).(3) Research on the single fumigant in gingerField trials in ginger indicated that single fumigants Pic and DZ both sharply reduced the R. solanacarum and maintained high ginger yields. Pic and DZ treatments did not express significant difference from MB with respect to R. solanacarum control, plant mortality, plant vigour and ginger yield. The recommended application method and dosage were Pic injection(50 g a.i. /m2) and DZ soil mixture(80 g a.i. /m2).