Phytotoxicity of BHC to Cotton

Abstract

Since BHC sprays caused toxic symptoms on cotton in the course of field trials in Uganda, the effect of the compound was investigated on early-planted cotton in 1951. Sprays containing 0.065 and 0.025 per cent γ BHC, prepared from a 6.5 per cent dispersible powder or from a 3 per cent emulsion concentrate were applied when the plants were 4-12 weeks old at 30-150 gals, per acre, according to the size of the plants, and symptoms leading to leaf mosaic and plant stunting were observed a week later. Individual plants varied greatly in susceptibility, but there was no evidence of differences in phytotoxicity between the two formulations. The age of the plant did not affect its susceptibility, but only young green tissue was affected. Leaves more than one inch long at the time of spraying and those that developed after it showed no symptoms. A single application at the lower concentration had little effect, but repeated applications caused some mosaic. A single application at the higher concentration frequently caused mosaic, and stunting was common when the treatment was repeated at weekly intervals. The weight of green bolls was not reduced, even on the plots that had shown the most severe symptoms, and it was therefore concluded that BHC applied at normal rates should have no harmful effects on yield. This was confirmed later in the year, when sprays of 0.025 per cent γ BHC applied once a fortnight during most of the growing season caused no harmful effects and only slight visible symptoms. Laboratory experiments showed that root growth was much reduced when cotton seedlings were grown in a culture solution containing small amounts of γ BHC from the emulsion concentrate, but it was much less affected by the same amount of γ BHC (purified) from an acetone solution. In a discussion of these results, it is pointed out that the sprays might have affected the cotton through the action of the γ isomer as a growth-promoting substance [cf. R.A.E., A 40 81] or through the development of phytotoxic breakdown products of BHC [cf. 38 445]. Since preparations of the pure isomer only slightly affected the growth of the seedling roots, breakdown products were probably responsible.