Nematodes are unsegmented, mostly microscope roundworms that are ubiquitous in soils.  More than 80,000 different nematodes have been described. Most species of nematodes rely on bacteria, fungi, or other microscopic organisms for food, and, therefore, are a key feature of healthy soil ecosystems. Additionally, some nematodes are beneficial to plant health by virtue of their ability to feed on plant pathogens or insect pests. Nonetheless, some nematodes parasitize plants, causing more than $50 billion in crop losses annually.   

Plant parasitic nematodes have a stylet, or mouth-spear, similar to a hypodermic needle. The stylet is used to puncture plant cells and inject digestive enzymes and other fluids. The nematode then draws plant fluids through the stylets. The most problematic nematodes are the root knot nematode, which feeds on more than 2000 species of plants including most major crops, and the cyst nematode which is an important pest in soybeans and potatoes. More than 50% of all nematode control efforts are aimed at these two types of nematodes. 

Historically, the most effective products for nematode control have been fumigants, particularly methyl bromide. With regulatory pressure to reduce or eliminate these fumigants, biopesticides have begun to emerge as alternative treatments to limit nematode damage.

Nematologists have identified several bacterial and fungal products for control of soil nematodes, as well as plant extracts that display nematoxicity or control the pest indirectly by boosting the natural defenses of crop plants. As fumigant nematicides continue to be phased out, biopesticides will play an ever-increasing role in control of these important pests.