Effect of DBCP pre-plant treatment on growth of replanted citrus

Abstract

Two 80-year-old citrus orchards, located at Yohchi and Issinden in Mie, Japan, were used for the experiments. These orchards were situated on a sloped land, and had a replant failure of citrus. Six experiment plots, 1×3m each, were set up in each orchard where Crossonema civellae, Pratylenchus loosi, and Tylenchulus semipenetrans were predominantly infesting. Treatment of soils at a half of each plot with 80% DBCP emulsifiable concentrate at 6ml/m² was made in April, 1970, and two-year-old Citrus unshiu plants grafted onto Poncirus trifoliata stocks were transplanted at 30cm intervals two weeks after treatment. Examination revealed that DBCP treatment significantly reduced nematode populations in both orchards, and this effect still remained to some extent in January, 1974 when the final examination was made. Treatment appeared to be phytotoxic, and growth of the replanted citrus was reduced in both orchards during the first two years, but in the third year the plants recovered their vigour and showed better growth than that of the untreated plots, although most plants situated at the lower part of the land at Issinden suffered severe damage from cold during the second winter. Correlation between the final nematode population and the weight of the above-ground part of citrus was evident at Yohchi. Necrosis of the feeder roots caused by Pratylenchus severly occurred in the untreated plots, and some incidence of the disease on roots was observed in both plots.