Abstract
The influence of fertilizers on host plants and the occurrence of the root-knot nematode, and on the efficacy of nematicide were investigated. Tomato (cucumber in the next year), red clover and sweet-potato plants were cultured with compound fertilizers alone (400g/3.3m2), with compost manure alone (30kg/3.3m2), and without fertilizers for 2 years. Nematode population density in soil, fecundity of adult females, and emergence of adult males and brown egg masses were estimated. Nematicide EDB was applied at the time of harvesting or in the next spring to each plant. After the nematicide application, sweet-potato plants were cultured in all plots with habitual fertilization (chemical compound fertilizers 100g/3.3m2, compost manure 10kg/3.3m2). The results were as follows: (1) The increases in small male adults with one testis and in brown egg masses were accompanied with the rapid maturity of the nematode on plants without fertilizers. The larval density in the soil was maximum in the early growing stages of these plants. (2) The peak of larval density occurred in the latter half of plant growth receiving chemical fetilizers alone. Large males with two testes were increased. Continuous application of chemical fertilizers caused an increase of the nematode population. (3) Larval density in the plot with compost manure reached its maximum at the harvest time of the plants. (4) In the plot with compost manure, application of EDB in autumn (harvest time) was more effective than in the next spring. On the contrary, spring application in the plots with chemical fertilizers alone or without fertilizers was rather effective than previous autumn applications.
