The eradication of weeds in cereal crops by sulphuric acid and other compounds

Extract

In continuation of earlier work (2) on the destruction of annual weeds in cereal crops some thirty-four replicated experiments have been carried out during 1934 and 1935 in widely different localities. Besides sulphuric acid, nitric acid, ammonium and sodium hydrogen sulphates and ammonium thiocyanate were tested, while the effect of a wetting agent was also studied.

In every experiment the solution was applied by means of a knapsack sprayer at the rate of 100 gallons per acre. In general at the time of spraying the weeds were in the seedling stage, and the cereal crop not more than 6 in. high. Counts of the weed density were made in order to estimate the degree of control, while in the majority of the trials the yield of the cereal was determined.

Sulphuric acid at a concentration of 9·2 per cent. (1 gm. H₂SO₄ per 100 c.c.) gave a 90 per cent. control of Brassica arvensis (average of nine experiments) and when a 13·8 per cent, strength was used it gave a 95 per cent, control of Raphanus raphanistrum (average of eight experiments). Nitric acid at equivalent concentrations was slightly but significantly more effective in three out of nine trials for the eradication of these two species. Ammonium hydrogen sulphate (21·6 per cent.), sodium hydrogen sulphate (23·6 per cent.) or ammonium thiocyanate (3–10 per cent.) did not, on the whole, compare favourably with sulphuric acid. Decreasing the concentrations of sulphuric acid by a third resulted in a less effective destruction of Brassica arvensis or Raphanus raphanistrum. This loss of efficiency at the lower concentrations was not corrected by the addition of a wetting agent (Agral 1 at 0·1 per cent.); similar results were obtained for nitric acid.