Table 1. 2,4-DlCHLORO-3,5-DINITROBENZOATES Ester m.p. Formula AnalysisFound (%) Required (%) C H C HMethyl Ethyl Isopropyl 84 101 117 CHeClaNjo C10H8C12N206 32-9 35-2 37-3 1-1 1-6 2-5 32-5 35-0 37-15 132-5 We have examined simple aliphatic esters of 2,4-di-chloro-3,5-dinitrobenzoic acid5 (Table 1) as protectant foliage sprays in the greenhouse for the control of Alternara solani on tomatoes, Erysiphe graminis on oats and Peronospora tabacina on tobacco. A standard greenhouse test6 was used for assessing control of A. solani and basically similar techniques were adopted with E. graminis and P. tabacina. The benzoates (prepared by Fischer esterification of the parent acid) were fungitoxic (Table 2). The methyl ester in particular gave good control of the three pathogens and in a more detailed examination against A. solani it had an ED95 value of 0-01. Tetra-methylthiuram disulphide in the same experiment had an ED95 of 0-08. The free acid was much less active, presumably because the presence of the polar carboxy group reduced the ability of the molecule to penetrate the fungal cells.Table 2. FUNGITOXICITY OP 2,4-DiCHLORO-3,5-DiNiTROBENzoATES Ester Concentration (p.p.m.) Disease (% of unsprayed control)A. solani E. graminis P. tabacina Methyl Ethyl Isopropyl Free acid 500 100 500 100 500 100 500 1 1 0 4 25 75 100 0 0 0 1 0 0 30 0 10 60 80 20 40 100We detected no phytotoxicity with these compounds at 500 p.p.m., the highest concentration tested, nor did we observe symptoms of plant growth effects known to be associated with certain halogenated nitrobenzoic acids and their esters7"8. The reactivity of the halogen groups is almost certainly responsible for the fungitoxicity of the 2,4-dichloro-3,5-dinitrobenzoates. In this respect their mode of action probably resembles the pathways of fungitoxicity suggested for chloranil, dichlone9-11 and 2,4-dinitrofluoroben-zene12, where labile halogen atoms are considered to react with essential amino or mercapto groups in the microorganisms. This view is supported by the knowledge that the elimination of the chlorine atom of 2,4-dinitrochloro-benzene by amines13 or mercaptans14 occurs in mild conditions. Likewise, both the chlorine atoms of methyl 2,4-dichloro-3,5-dinitrobenzoate were readily replaced, for example, by methylamino and phenylthio groups to give methyl 2,4-di(methylamino)-3,5-dinitrobenzoate (m.p. 2080/ Found: N, 19-7. C10H12N4O6 requires N, 19-7 per cent) and methyl 2,4-di(phenylthio)-3,5-dinitrobenzoate (m.p. 104. Found: C, 54-4; H, 3-2. C2,H14N2O6S2 requires C, 54-3; H, 3-2 per cent) respectively. Neither reaction product was fungitoxic at 500 p.p.m.