The influence of soil disinfection with DD, certain components of DD and some other compounds with nematocidal activity on the growth of white clover

Abstract

In pots containing soil fumigated with DD before planting the growth of white clover was considerably better than in untreated pots. A similar effect was obtained both with cis- or trans-1,3-dichloropropene. Some other components of DD, including 1,2-dichloropropane, had no influence on clover growth in the concentration at which they occur in DD. Of the compounds not associated with DD, EN 18,133 and sugar showed a favourable effect on clover growth, but X 323 had no influence. In the untreated pots with poorly growing clover many roots had died. On the places where dead lateral roots had been attached many fungi were present in the tissue, especiallyRhizoctonia sp. andFusarium spp. These pots contained also more clover cyst nematodes and more springtails (Collembola). In one of the pot experiments poor growth could probably be attributed to an attack by the clover cyst nematode (Heterodera trifolii Goffart). The nematode level above which damage to the plants occurred was calculated at 1000–3000 eggs (larvae inclusive) per 100 ml of soil. In the other pot experiment, however, poor growth could not be explained by cyst nematodes only. In field experiments clover growth was promoted by soil fumigation with DD, also when only a few cyst nematodes were present. These observations increase the evidence that attack of white clover by pathogens is a complex phenomenon in which nematodes as well as fungi and perhaps insects too are involved. Apart from a small increase in growth at the beginning, soil fumigation with DD did not raise the yield of perennial rye grass.