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Field studies of potato crops under different soil and fertility conditions and exposed to attack by diverse concentrations of potato-root eelworm led to the following conclusions:

In the north-western agricultural advisory province potato-root eelworm is not a major cause of failure or partial failure of potato crops on land where the viable cyst concentration is low (under 10/10 c.c. of soil). On such land increased yields can be obtained by improving conditions for plant growth, widening the rotation and increasing the fertility of the soil.

The production of satisfactory crops on land with a low eelworm population is likely to be accompanied by considerable increases in the numbers of root eelworms in the soil.

Crops free from signs of ‘potato sickness’ or ‘potato-root eelworm disease’ can be grown on land heavily infested with root eelworms (viable cyst concentration exceeding 25/10 c.c.), if no other adverse condition, such as unsuitable weather, lack of available food or incidence of fungus disease, affects the growth of the crop, but yields from heavily infested land are not likely to be more than moderate.

The treatments used against eelworms in the trials described here did not give results commensurate with their cost.

The practical difficulties of incorporating lethal substances with soil in the field are considerable, and this may have contributed to the disappointing results obtained.

The study of the influence of host variety on cyst production suggests that varietal differences in the host plants may influence the numbers of cysts formed on the crop, but the evidence is not conclusive.