THE USE OF TETRA- AND PENTA-CHLORONITRO-BENZENES IN THE CONTROL OF BOTRYTIS DISEASE AND RHIZOCTONIA ATTACK OF LETTUCE

Botrytis disease in the 'spring' lettuce crop was controlled by six talc dusts containing s, 10 or 20 % of tetra- or penta-chloronitrobenzene. All the dusts increased equally the final stand in the frames, but the number of seedlings with stem lesions decreased with increasing concentrations of both compounds. At similar concentrations the tetra- was more effective than the penta-compound. The percentage survival in the field was increased by the dust treatments. The 20% dust of the penta- was only as effective as the 5% dust of the tetra-compound.
The dusts affected the leaves, stunted the seedlings and delayed hearting. At similar concentrations the tetra- was more harmful than the penta-compound. The 5 % dust of the tetra- was less damaging than the 20% dust of the penta-compound.
The spread of Rhizoctonia solani was reduced by incorporating the dusts with soil. Again, the 5% tetra- dust was as effective as the penta- dust at 20%. At 12·5 g. of dust per 20 kg. of soil, none of the dusts retarded the rate of emergence of lettuce seedlings but the highest concentration of the tetra- series reduced the number emerging.
Foliage applications of two dusts, 5% tetra- and 20% penta- dusts, controlled the spread of R. solani.