Role of sampling for crop-loss assessment and nematode management

Reliable sampling of nematode communities in crop-loss assessment provides basic characterization of the population dynamics and damage potential of given species in a particular host—cultivar environment. Loss assessments for annual plants may be based on samples taken at: (1) time of planting; (2) mid-season (where nematicide or resistant-cultivar treatments are used); and (3) at harvest. Population levels at, or shortly after, harvest are most useful in projecting nematode hazards for a subsequent crop, especially where survival rates are known. Root symptoms, root-gall or root-necrosis indices, taken at mid-season or at harvest also can be correlated with yield losses caused by Meloidogyne spp. and associated fungi. A composite sample of 20 to 50 soil cores (2.5 cm diameter × 20 cm deep) collected in a stratified or systematic pattern over a 1- to 2-ha area provides nematode population estimates within about 30–50% of the mean. The major problems encountered in relating these estimates to potential hazards and eventual crop losses are related to the striking variation in crop-nematode responses as influenced by environment, cultivar, and general crop-management practices. Relative precision in crop-loss assessment should be improved as more research on crop-nematode responses and sampling methodology is completed.