Effects of four fungicides on soil fusarium oxysporum population and enzymes activity in successive cropping apple orchard

【Objective】The apple trees grow poor when they are planted in old orchard,which is becoming more and more serious,so the research on apple replant obstacles was necessary. The study was to screen out high efficient,but low toxic chemical fungicides which mixed with soil to deal with successive cropping obstacles.【Method】Field treatments included four fungicides with replant soil i.e. carbendazim 10 g a.i/10 kg soil,thiram 10 g a.i/10 kg soil,fludioxonil 2.5 g a.i/10 kg soil,mancozeb 10 g a.i/10 kg soil and four fungicides with inter-row soil i.e. carbendazim 5 g a.i/5 kg soil,thiram 5 g a.i/10 kg soil,fludioxonil 2.5 g a.i/10 kg soil and mancozeb 5 g a.i/10 kg soil. The changes of Fusarium moniliforme Sheldon population and enzyme activity after treatments were observed.【Result】Toxicity test of four fungicides to fusarium oxysporum showed that fludioxonil was the best in control of soil Fusarium oxysporum with EC500.356 mg·L-1. Fludioxonil could reduce the replant and inter-row soil Fusarium moniliforme Sheldon population by 80.17%and 86.48% resectively. The results on tree biomass showed that: mancozeb increased the shoot number,stem diameter,leaf number,shoot length and leaf area of plants in the replant floor by 2,1.27 cm,10.84,27.54 cm,9.84 cm2,and in the inter-row floor by 1.92,1.00 cm,14.26,22.19 cm,5.55 cm2. Its effect was better than the other chemicals. The results on enzymes showed that:fludioxonil was the best for the increase of catalase acitivity; carbendazim was the best for Invertase; thiram was the best for neutral phosphatase; carbendazim was the best for Urease. All soil enzyme activity decreased in August,and activation of fungicides disappeared.【Conclusion】Fungicides could effectively inhibit the growth of soil Fusarium and alleviate replant problem.