any one of various parasitic roundworms of the family Tylenchidae that cause disease in rice. The nematode Ditylenchus angustus causes ring disease. The females are 0.7-1.2 mm long, and the males 0.6-1.1 mm. The nematode is distributed in India (Bengal and other regions), Egypt, and the countries of the Malay Peninsula. It is not found in the USSR, where it is an object of quarantine. The parasite inhabits leaf axils, lemmas, and growing points. It feeds on young tissues and plant juices by boring through cells. There are no fewer than three generations in a summer. With severe infestation many plants die, thereby sharply decreasing the rice yield. In some places the entire crop is destroyed by the nematodes. The parasites mainly infest late-maturing varieties of rice raised from seed; early maturing varieties raised from transplants are damaged considerably less.
The rice nematode Aphelenchoides besseyi, or A. oryzae, causes the disease known as white tip.
For a discussion of control measures seeNEMATODE PLANT DISEASE.