David M. Wichman

Plant-Parasitic Nematode Problems in Organic Agriculture

Crop protection approaches differ widely among organic growers both globally and regionally, yet organic farming faces the same plant-parasitic nematode (PPN) issues as conventional farming. Due to the restrictions on use of synthetic chemical inputs and the limited number of options for nematode management in organic fields, organic producers are often at greater risk to nematode problems than their conventional counterparts. While worldwide estimates of crop losses of about 12 % annually of food and fiber due to nematode damage are reported in the literature, such information for organic farming systems is scarce. Comparative studies of organic and conventional farming systems and surveys conducted in organic farms in distinct regions show that the genera of nematodes attacking organic crops are similar to that in conventional fields, including species of root-knot (Meloidogyne spp.), cyst (Heterodera and Globodera spp.), and root lesion (Pratylenchus spp.) nematodes, among others. For PPN management, organic farmers employ practices such as crop rotation, use of cover crops or resistant crop cultivars, and soil amendments. In many instances, however, these methods may not be sufficient for PPN management. Although resistant cultivars of some crops are available for root-knot and cyst nematodes, they are resistant to only a few races or species of nematodes and new races develop over time. Biological control, using microbial pathogens, endophytes, or antagonists may help control PPNs in organic production of some crops but have had limited commercial success. In contrast, use of soil amendments has provided some level of suppression of PPNs under field conditions. Increased populations of predatory nematodes or other beneficial species grazing microbial films and stimulating soil nutrient mineralization have been observed in organic systems, indicating an improvement in the soil health. Further studies are needed to estimate yield losses caused by the economically important PPN species in organic systems and to develop suitable nematode management strategies given for organic farming.