Study on occurrence dynamics of yam root-knot nematode disease and its control technology under root irrigation

Root-knot nematode disease is a stubborn and easily recurring disease in yam production and severely restricts the high-quality development of the yam industry. To develop an accurate control technology, this study focused on Ruichang yam and established test sites in Ruichang and Nanchang of Jiangxi Province for the collection and identification of the different root-knot nematodes. Population dynamics of the 2nd instar larvae (J2) of root-knot nematode were observed in the soils and the dynamics of nematode infection on yam were monitored in the fields for the determination of the appropriate control periods and the development of effective spraying technology in the fields. The result indicated the nematode isolates in the soils were southern root-knot nematode (Meloidogyne incognita). The J2 populations showed a continuous increase during the whole growth period of yam in the soils. Yam root infections by root-knot nematode occurred mostly in late May (seedling stage) and sick yam tubers appeared in mid-to-late June, then, the severity of the sick yam tubers continued to increase significantly. The critical periods for root-knot nematode control were at the neatly-grown seedling stage and the following 60 days and one application for each. The control efficacy of 41.7% fluopyram suspension (active ingredient amount 1426 g/hm²) and 30% thiazophos microcapsule suspension (active ingredient amount 2925 g/hm²) were 81.56%-83.43% and 75.95%-77.16%, respectively. The application of 30% thiazophos microcapsule suspension (active ingredient amount 2925 g/hm²) combined with 10 billion spores/gram of Bacillus firmus wettable powder (active ingredient amount 12000 g/hm²), and 41.7% fluopyram suspension (active ingredient amount 1426 g/hm²) with newly generated twice uniform root irrigation technology improved the control efficacy to more than 81%, which is significantly higher than the combination of drip irrigation at the early stage and root irrigation at the later stage, two drip irrigation and two conventional root irrigation.