A D-D mixture was tested against the Root-Knot Eelworm, Heterodera marioni (Cornu), in a glasshouse devoted to the growing of tomatoes under commercial conditions in South Wales. The effects of four different rates of application, namely, 0, 200, 300 and 400 lb. per acre injected at a depth of seven inches at staggered points fifteen inches apart were investigated.

Improvements in growth of the tomatoes and reductions in the eelworm manifestations on the roots were produced in proportion to the increases in the dosage rate. Height of the plants, number of flower trusses and yield of fruit were selected for actual measurements of the effects produced on the growth of the tomato plant. All of them showed a graduated response to the injections at 200, 800 and 400 lb. per acre, the yields of marketable tomatoes, for example, being at the three dosage levels, respectively, about 200, 850 and 450 per cent. higher than in the controls.

The nematocidal effects were measured independently by grading the roots into four distinct categories, according to the severity of the pathological manifestations associated with the presence of Heterodera marioni. Judging by the results obtained in this way, D-D reduced the infestation by something like 25, 50 and 75 per cent, when injected at the rate of 200, 800 and 400 lb. per acre respectively. No information regarding the quantity necessary to effect complete extermination is available but it seems that an application exceeding 400 lb. would be imperative for this purpose at least in heavily infected soils where 70 per cent, of the plants are liable to suffer severe infestations.