STUDIES ON SYSTEMIC FUNGICIDES

A number of mono-, di-and trichloro-β-naphthols and the corresponding naphthyloxy- n -carboxylic acids were prepared. They were tested as systemic fungicides against chocolate spot of broad bean ( Vicia faba ) caused by Botrytis fabae and as fungicides in vitro by their effect on the germination of spores of Sclerotinia laxa and the growth of the mycelium of Botrytis fabae.
The systemic fungicide tests showed no difference in the activity of the compounds associated with different side chains, though there were slight but significant effects associated with different chlorine substitutions in the naphthalene nucleus. The 3:4-dichloro-2-naphthol derivatives were more effective than the other compounds tested.
Fungicide tests with the 1:3-dichloro-2-naphthol derivatives suggested that there was some increase in toxicity to the spores of Sclerotinia laxa with increasing length of side chain. The effectiveness of the various chlorine-substituted compounds in suppressing growth of Botrytis fabae was in the following descending order, 1:3:4-trichloro-, 1:3-dichloro-, 1:4-dichloro-and 3:4-dichloro-compounds. The concentrations required in agar culture to induce reductions of B. fabae growth comparable to those found in the leaf could reasonably be expected to occur in the bean plants treated with the 2-naphthyloxyacetic acids at 10 p.p.m.