Crops and soils from a large number of field trials have been analysed for residues of 2,6dichlorothiobenzamide (chlorthiamid) and for residues of 2,6-dichlorobenzonitrile (dichlobenil).
The thiobenzamide is converted to the benzonitrile after application to the soil and only a small percentage of the material applied initially remains unchanged after 4 weeks. However, both the benzonitrile and the thiobenzamide are of similar low mammalian toxicity.
The initial half-life of the 'total nitrile' residues (the thiobenzarnide + the benzonitrile) is, on average, near 4 weeks but varies from 1 to 12 weeks depending on the locality, soil type, climate, dosage level and formulation.
The penetration of the herbicide into soils of different types is considered and it is shown that in sand, loam, and clay, residues in the 4 1 2 in. layer are less than 10% of the residue at the same time in the 0-4 in. layer.
Residues of the thiobenzamide and the benzonitrile could not be detected in a very wide range of crops (other than rice) harvested at 2-6 months after soil applications of the thiobenzamide at 1-16 Ib/acre. In rice grains, where the plants can be in intimate contact with the herbicide, the 'total nitrile' residues did not exceed 0.05 ppm.
* Combined residues of benzonitrile and thiobenzamide expressed in terms of benzonitrile ** After clean-up by column chromatography ??Second annual application