The Formulation Of Disancu As A Mixtured Bioherbicide

The fungal plant pathogen Curvularia eragrostidis strain QZ-2000, isolated from naturally infected large crabgrass (Digitaria sanguinalis), was virulent against large crabgrass and evaluated as a potential bioherbicide for the control of Digitaria species. Disancu was a bioherbicide developed by Weed Research Lab., Nanjing Agriculture University with the conidia of strain QZ-2000 as its major bioactive component. And Disancu has already applied for a patent. Preliminary studies showed that the fungus conidia were easy-to-industrial production. In addition, C. eragrostidis strain QZ-2000 was strong pathogenic to some other gramineous weeds such as Chinese leptochloa, barnyard grass and so on. On the other hand, it is safe to rice, corn, soybeans and other crops. So the bioherbicide -Disancu had a great potential into commercialization. The purpose of the study was to improve some key techniques for the storage of conidia, the formulation and the use of Disancu under field condition.Firstly, the preservation time of the conidia of strain QZ-2000 under different store condition was studied. The conidia were stored separately or in rapeseed oil with different proportions at both room temperature and at 4℃. The germination and pathogenicity of conidia were tested periodically. The result showed that the conidia stored at room temperature lost their germinative activity and almost died one year later. But the germination rate of the conidia was over 80% and the conidia keep high pathogenicity to crabgrass when stored at 4℃ for one and a half year. The colza oil has little effect on conidia stored in different condition.One of ways to enhance bioherbicide efficacy were to integrate the biological and herbicidal control. We investigated the direct effects of a range of chemical herbicides used in different crop fields upon conidia of C. eragrostidis and found that some herbicides were strongly inhibitory to germination of conidia. On the other hand, C. eragrostidis was compatible with a selection of poste-mergence herbicide, including pendimethalin, nicosulfuron, fluoroglycofen, and Butachlor·Oxadiazon. These herbicides have no significant influence on the germination rate and pathogenicity of the conidia. The efficacy of C. eragrostidis to control large crabgrass can be enhanced by use of these chemical herbicides with low dosage.Now, the formulation of Disancu was a wettable powder. But there are some constraints in use of this solid formulation in the field. To solve the problem, a lot of adjuvants were tried in this study to make Disancu into a water-in-oil-in-water (W-O-W) emulsion. The emulsifier SG-40, the humectant GY-W04, and the dispersant GY-NDS were found that can be used to develop the W-O-W emulation, with the optimal dosage 125g, lOg and 10g per 667m2.The green-house experiments were carried out to evaluate the efficacy of Disancu combing with certain chemical herbicide. The results showed that the control effect of crabgrass can achieve about 80% if use 6×105-1×106 conidia/ml integrating 1/10 or more of recommended field dose of chemical herbicide. We also did some field experiment to assess the efficacy of the bioherbicide when applied under natural conditions. The results showed that the control effect of crabgrass affected by environmental factors significantly. To take cost, effect and some other factors into account, the preferable control can get when the conidia concentration of 8×105 conidia/ml combined with low dosage nicosulfuron (1/8 of recommended dosage) be used. And the number and fresh weight reduction were over 75% and 60% separately.In summary, an appropriate formulation can reduce the dew dependence of bioherbicdes. And combined bioherbicide with chemical herbicide can enhance the efficacy of weed control.