AbstractThe studies of the eradication of barley mildew due toErysiphe graminisMérat with alkyldinitrophenols reported earlier1were continued. The degree of eradication was highest with 4‐(C9α‐branched alkyl)‐2,6‐dinitrophenols. 4‐Alkyl‐2,6‐dinitrophenols containing a heptyl or higher alkyl branch were significantly less active, and compounds containing the C12or C13alkyls were not active since the most compact of the C12α‐branched alkyls is 1‐pentylheptyl. 2‐(1‐Methylheptyl)‐ and 2‐(1‐propylpentyl)‐4,6‐dinitrophenols had high activity, but their esters showed reduced activity. Esterification of 4‐(α‐branched alkyl)‐2,6‐dinitrophenols to methyl carbonates did not affect the activity shown by the compounds, but when certain 4‐C10and C11alkyl‐2,6‐dinitrophenols were esterified to ethyl carbonates the activity of the products was reduced. Also activity was diminished by conversion of some 4‐C9and C10alkyl‐2,6‐dinitrophenols to crotonates. Whereas the methyl‐ and ethyl‐ carbonates of 4‐(1‐ethylhexyl)‐2,6‐dinitrophenol gave consistently high degrees of eradication of barley mildew, the performance of the crotonate of this phenol was not consistent. Lower aliphatic esters of the active C8‐alkyl phenols were themselves active. Esterification of 4‐(1‐ethylhexyl)‐2,6‐dinitrophenol to the benzoate, isopropyl carbonate orS‐methyl thiolocarbonate gave compounds with substantially reduced activity. 2‐t‐Butyl‐4,6‐dinitrophenyl or 4