| Raising crab in paddy-field, a stereoscopic eco-agriculture model with better economical benefit, is a new cropping pattern that can improve agricultural increment and farmer's income. Now it has a better trend in China. But so far as little has been done on the plant protection innocuous techniques in rice-crab fields. In order to optimize the integrated pest control pattern of diseases, pest-insects and weeds in rice-crab field, this paper dealt with some research work as follows.(1) Occurrence of major diseases, pest-insects and weeds in rice-crab field were surveyed. Results showed, compared to monoculture paddy-field, the population density of rice planthoppers (including Nilaparvata lugens, Sogatella furcifera and Laodelphaxstriatellus) was relative less and always lower than the level in monoculture paddy-field. Even the most population density of them was only 66% of the level in monoculture paddy-field; The rate of roll leaf caused by Cnaphalocrocis medinalis was about 2 times of that in monoculture paddy-field; The damage of Chilo suppressalis and Tryporyza incertulas was about 2-3 times of that in monoculture paddy-field and even more; The incidence of rice sheath blight was about 5% and the disease grade is relative less; The disease index and incidence of rice blast were obviously less than those in monoculture paddy-field; The occurrence of weeds was relative less also.(2) Commonly used pesticides with big spread extension, highly active and low mammalian toxicity and low residue were selected and 60% of normal field recommended dosage of them were used in consideration of the fact that the area of rice planting was about 60% of our experiment plot. Plan A and plan B of plant protection were designed and their effects on pest control were evaluated in the experiment. The results showed: Plan A was better than plan B for rice blast control and the difference was significant; Both plan A and plan B were effective for rice sheath blight control and the difference was not significant; Plan A was better than plan B for C. suppressalis andT. incertulas control and the difference was significant; Plan A was better than plan B for rice plant hopper control and the difference was significant; None of plan A and plan B was very effective to control dominant weeds species. In addition, the results of evaluating yield indicated that the percentage increases of plan A was higher than that of plan B. So the results of control effect and evaluating yield indicated that plan A was better than plan B.(3) The crab's food-take to common weeds (Spirodela polyrrhiza, Echinochloa crusgalli and Juneceus serotinlls) and a common pest (N. lugens) were studied for the first time in China. The results showed: During the period of growth, crab has different food-take to the weeds at its early stage, the order of food-take was S. polyrrhiza> J. serotinlls> E. crusgalli. But with the development of crab, it was getting smaller and smaller, even no food-take; In designed N. lugens population density (5 ~ 40 heads/0.05m2, 0.012m3, 3 trunks of rice plant), the functional response was Holling-I. Three linear regression equations of experiment were as follows: Na=0.4167N-1.75, Na=0.4486N-2.0929 and Na=0.4505N-2.1857, the correlation coefficients all reached 0.99.(4) The safety of crab after triazophos treatment in rice-crab field was studied for the first time in China. The results of acute toxicity of triazophos to crab showed that 96h after treatment, LC50 was 0.189mg.L-1. Spraying experiment indicated that 38.12% of triazophos was dropped into paddy water after it was used with 60% of normal field recommended dosage. It was suggested that 50% or even under 30% of normal field recommended dosage of triazophos could be used, and other pesticides should be mixed in order to improve control effects and guarantee the safety of crab.(5) The residue analysis of fipronil in soil, rice, and crab was conducted. Firstly, we built a new pretreatment of soil and rice to meet the criterion of pesticide resi...
|
PDF Full Text Request