Control efficacy of several fungicides on pepper phytophthora blight and effects on rhizosphere microorganism

【Objective】 In this paper, the effect of different fungicides on the growth inhibition of Phytophthora capsici, pepper phytophthora blight field control and the yield increasing effect on pepper were studied, to screen out the fungicides which could effectively control the local pepper phytophthora blight and had little or beneficial effects on the rhizosphere soil microbial community structure of pepper, and provide technical guidance for pepper phytophthora blight control.【Method】 P. capsici-Ph2 was used as the test material. Fifteen fungicides were screened by mycelial growth inhibition. The six pesticides with growth inhibition rate of 100% were selected as the candidate agents. The high incidence plots of pepper phytophthora blight were used as experimental plots. The random plot experiment was designed to test the incidence rate, disease index and the control effect of pepper phytophthorablight at different times after irrigating the pesticide. The growth and yield indexes of pepper treated with different fungicides were measured at harvest time, and the yield increasing rate was calculated. Meanwhile, the rhizosphere soil of pepper was collected, and the colony numbers of soil bacteria, fungi and actinomycetes were measured by plate counting method. Bacteria/fungi ratios were calculated to explore the effects of different fungicides on soil microbial populations in the rhizospheresoil of pepper.【Result】 There were six fungicides with 100% growth inhibition rate to P. capsici, which were 33.5% oxine copper SC, 80% dimethomorph WG, 72% cymoxanil·mancozeb WP, 687.5 g/L fluopicolide·propamocarb hydrochloride SC, 23.4% mandipropamid SC and 64% oxadixyl·mancozeb WP. The field control effect test showed that fluopicolide·propamocarb had the best control effect on the 33rd day after root irrigation(93.86%), followed by oxadixyl·mancozeb(71.80%). There was no significant difference in the growth indexes of pepper among different fungicides treatments (P>0.05). The yield of fresh pepper was speculated to be the highest treated by oxadixyl·mancozeb(22.74 t/ha), followed by fluopicolide·propamocarb hydrochloride(21.29 t/ha), and their yield increase rate were 29.52% and 21.22%, respectively compared with control. Bacterial to fungal ratioswere cymoxanil·mancozeb>fluopicolide·propamocarb>oxadixyl·mancozeb>oxine copper>mandipropamid>dimethomorph. Bacterial to fungal ratio of cymoxanil·mancozeb (13.85) was the highest, and was extremely significantly higher than others(P<0.01). 【Conclusion】 Oxadixyl·mancozeb and fluopicolide·propamocarb hydrochloride have good control effect on pepper phytophthora blight, and have significant effect on increasing production. They have little effects on soil bacterial biomass, and can be used as fungicide for pepper phytophthora blight control.