Effects of repeated applications at high rates of chlorthiamid and dichlobenil to blackcurrants

Abstract

Chlorthiamid and dichlobenil were applied to blackcurrants each year for five years at doses up to 54 kg ha-1. Growth and yield were not affected but leaf margin chlorosis was caused at the higher rates. No nitrile residues of dichlobenil or chlorthiamid were found in the fruit but 2,6-dichlorobenzamide (DCB) was present in most samples tested. There were no adverse effects of the treatments on the taste and flavour of the canned fruit. Nitrile residues in the soil were largely confined to the top 15 cm layer. Amounts detected one year after the previous application did not increase with repeated treatments and were always less than 10% of the annual doses. Nitrile residues were less from dichlobenil than chlorthiamid. The rate of disappearance of soil residues present at the end of the 5-year treatment period was much slower than that of the freshly applied herbicide. During the period of treatment there was generally less DCB than nitrile in the 0-15 cm layer but more was found in deeper layers and small amounts were detected at all depths sampled (up to 105 cm). These residues had largely disappeared 3.5 years after the final treatment. Test crops sown on the plots two years after the final treatment varied in susceptibility to the residues as follows; barley and cabbage (unaffected) < wheat < lettuce < carrot (most susceptible). In the following year only the treatments with chlorthiamid at 27 and 54 kg ha-1 caused a decrease in the growth of carrots but all the treatments caused skin abnormality.

Persistence of dichlobenil in a sandy soil and effects of residues on plant growth

“…The NS: stand not significantly (P = 005) less than the control Table 4 Effects ofdichlobenil residues on mean yield of crops 1972 1972 1973 1974 1975 1976 1976 1972 1973 1974 1972 1973 1972 1972 1973 1974 1973 1974 1972 carrot-roots only lettuce, cabbage and barley-aerial parts sugar beet and radish-roots plus tops stand was reduced by 0-20 mg/kg dichlobenil but no reduction in yield was recorded below 0 60 mg/kg. Established ofthe radish crop was not affected by any treatments but yield was reduced by 0-60 mg/kg dichlobenil on the 16 6 kg/ha incorporated treatment, Barnsley (1960) and Clay (1978) also found carrots to be the most sensitive crop followed by wheat, barley and cabbage.…”