| Abstract: | The vapour phase and protectant activities of members of seven homologous series of alkyldinitrophenols against cucumber powdery mildew (Oidium sp.) are discussed. No correlation existed between vapour activities in vitro or in vivo and vapour pressure, but a positive correlation between Vapour' protection in vivo and conventional protectant activity was evident. Although vapour activity occurs with some homologues, results obtained for zone assays in vivo are probably better explained in terms of easy movement of the compound in the leaf surface than in terms of vapour transmission. Alkyldinitrophenyl-crotonates showed no zone activity in vivo but often good protectant activity. The possible existence of two optimum π-values for protectant activity is suggested. No appreciable systemic activity was found with these compounds. |
