| In order to develop green loquat production and to reduce pesticide pollution on environment, the loquat pests and their natural enemies were investigated and the residues in loquat orchard soil and loquat leaves of commonly-used chemical pesticides were analyzed, and in the meantime, the pesticide effects on soil enzyme and microorganisms were studied. An ecological control system of the loquat pests was established by means of general ecological control theory and evaluation indices. The general results are present as following: 1. Loquat pests and their natural enemiesThere are 16 orders in loquat arthropod community (consisting of 14 Insecta orders and 2 Arachnoidea oeders) and 56 pest species and 35 natural enemies species are found among them. In Fujian Province, Melanographia flexilineata Hampson, Phalera flavescens Bremeret Grey are primary pests feeding on loquat leaves, and Grapholitha molesta Busck, Rapala varuna Horsfield, Homona coffearia Nietner and H. nakaoi Yasyda are primary pests feeding on loquat fruit. The best control period of P, flavescens, M. flexilineata, G. molesta is from June to September, July to August, and April to May respectively. The appropriate time for the mass rearing and releasing of parasitic wasps can be known based on the development period studies. G molesta presents ecological selection trend from different loquats: It prefers to damaging "Wugongbai" and "Jiefangzhong" than to "Baili" and "Zaozhong No.6". 2. Chemical Effects on loquat pests and natural enemiesMost of broad-spectrum chemical pesticides show the good control effects on Melanographia flexilineata Hampson and Grapholitha molesta Busck., but they are harm to the natural enemies such as Chrysopidae, Coccinellidae and Arachnoidea insects. It shows that the chemical pesticides strikingly decrease the natural enemies and restrains the control effects of natural biological agents on the pests.3. Effecte of pesticide residues on soil and loquat leavesThe residues of thiophanate methyl in the loquat leaves are moderate. Its degrading rates is 47.57% in one day, 65.99% in 7 days, and 85.96% in 28 days. The residue time in the soil is shorter than that in the loquat leaves.The degrading rates of fenvalerate in the loquat leaves is 84.77% in 7 days, and its residue can not be detected in 28 days, but in the loquat orchard soil it still exists. The residue time in the soil is longer than that in the loquat leaves. Two kinds of pesticides, thiophanate methyl and fenvalerate, have different action mechanism.4. Chemical pesticide effects on the soil enzymeThe different concentrations of thiophanate mentyl, fenvalerate and mancozeb avermectin have different effects on the enzymatic activities of soil catalase, urease, phosphate and invertase. The inhibition rate of soil enzymes increases with the pesticide concentration, but fenvalerate can increase the activity of soil urease.Avermectin has least effect on soil enzyme. The soil enzyme is inhibited at beginning and then becomes activated or retried with different time control. Soil enzymatic activity is positively to the pesticide concentration. The two kinds of pesticides might have different action mechanisms.5. Effects on soil enzyme by different control waysThe enzymatic activities of soil catalase, urease, phosphate, invertase in the ecological control orchard is higher than those in the chemical control orchard. Under different modes of cultivation and fertility, ecological control orchard has higher soil enzyme activity and resistance activity than the chemicals. Biological pesticides used in the ecological control orchard shows less toxicity to soil enzyme than chemical pesticides.6. Chemical pesticide effects on soil respirationUnder three concentration treatments of thiophanate methyl, fenvalerate, mancozeb, the release of CO2 is higher than the control at beginning, and it becomes lower than the control in 5 days, the lowest in 7-10 days, and then, it...
|
PDF Full Text Request