Investigation Of Sodium Tetrathiocarbonate As A Potential Fumigant For Vegetable Soilborne Disease Management And Its Effect On Soil Biological Environment

Sodium tetrathiocarbonate (STTC) is a potential soil fumigant. The efficacy of STTC to control soil-borne pathogens was evaluated with dosage-response study in laboratory. The effect of STTC on pepper Phytophthora blight and cucumber Fusarium wilt was studied in the pot and field trials. Effects of STTC on the population of the soil microbes and activities of soil urease, invertase and proteinase were also investigated.Laboratory dosage-response study showed that the LD50 of STTC against Phytophthora capsici, Fusarium oxysporum, Verticillium dahliae, Rhizoctonia solani and Sclerotinia sclerotiorum were 3.9555 mg, 4.2412 mg, 5.2224 mg, 5.4572 mg and 6.1972 mg/kg, respectively. Pot trials showed that STTC used as a pre-planting fumigant at 80g/m2 suppressed pepper Phytophthora blight and cucumber Fusarium wilt by 90.89% and 82.6% , respectively, samilar as dazomet at 30g/m2 (P=0.05) . Populations of the pathogens were significantly reduced when STTC was applied by pouring at the distance of 10cm from pepper and cucumber root at 1200μg/mL×200mL as a post-planting fumigant. At the 10th day and thereafter the suppression rate in rhizosphere was almost the same as that at the treated sites. Safety tests showed that soil treatment immediately before transplanting with STTC at less than 1200μg/mL did not injure 3-leaf stage seedlings of tomato, pepper and cucumber. It was safe to the 3-leaf stage seedlings of cabbage and rape when STTC was applied to treat the soil at concentration less than 900μg/mL.Author investigated the impact of STTC on soil culturable microbial population by plate-dilution method. Results demonstrated that the soil culturable fungal population was reduced significantly in all STTC treatments during the investigation. Population of soil culturable bacteria and actinomyces were reduced at early stage of treatment, and the inhibited level and duration was proportional to the concentration of STTC applied. As time went by, the inhibition was gradually replaced by stimulation. The stimulated level to bacteria was more significant than that to actinomyces.Tests on activities of soil enzymes demonstrated that urease activity decreased in initial 7th days and then gradually increase after 15th day of STTC treatments. Similar to soil urease, the activity of invertase was inhibited at 15th days and then stimulated from the 21th day. But the level of stimulation was negatively proportional to concentration of the STTC used. Proteinase activities was increased when STTC was used at lower dosage(0.1 and 1μg/g soil), but inhibited at first, then stimulated from the 21th day after treatment with STTC at higher concentration(5, 10, and 50μg/g soil). Until completion of the investigation, the activity of soil proteinase with high concentrations was signficant higher than untreatment.