Ketonitriles of the general formula ##SPC1## In which R.sub.1 and R.sub.2 signify alkyl groups with one to four carbon-atoms, R.sub.3 and R.sub.4 are hydrogen atoms or alkyl groups with one to four C-atoms and wherein R.sub.3 and R.sub.4 may also together form a carbocyclic ring preferably with five or six C-atoms and n is zero, 1 or 2 produced by condensing diols of the formula ##SPC2## With cyanaldehydes of the formula wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and n have the same meanings as set forth above, in the presence of strong acid catalysts where the diols may be in the thickly liquid, impure form. These ketonitriles are useful as herbicides.
The invention provides a method for controlling insect pests at a locus which comprises applying to said locus a compound of the formula I ##STR1## wherein R.sub.1 and R.sub.2 both represent a methyl group or together represent a tetramethylene or pentamethylene group and R.sub.3 represents a phenyl, 3-chlorophenyl, 4-chlorophenyl, 3,4-dichlorophenyl or 4-fluorophenyl group.
