IPMP3.0, Oregon State University, Copyright 2000



[Table of Contents]


Relative Sizes of Nematodes
Size of nematodes parasitizing mint in relation to the tip of a No. 2 pencil.

Modified from Russell Ingham and Kathy Merrifield. 1996. A Guide to Nematode Biology and Management in Mint. Integrated Plant Protection Center, Oregon State University, Corvallis. Pub. No. 996. 38 p.

Nematodes are nonsegmented round worms which are not related to earthworms and are generally considered as a distinct phylum of classification. Only slightly more than 15,000 species have been described but more than 500,000 different species are suspected to exist. Nematodes range in length from 3/1000 of an inch (found in ocean mud) to 27 feet (parasite in the placenta of whales). Species found in soil or plant material average about 1 mm (4/100 in) in length. Parasites of mint range in size from 1/2 mm to 5 mm.

Nematodes are one of the most ecologically diverse animal groups on earth and can be found in habitats from the tops of mountains to the deep ocean sediments and from hot deserts to Antarctica. Different species of nematodes may eat algae, bacteria, fungi, yeasts, diatoms or several kinds of small animals in soil or sediments. There are even large nematodes that eat smaller nematodes. Nematodes may be parasites of invertebrates, such as insects, or of vertebrates, including man. Many serious tropical diseases of man and many diseases of domestic animals are caused by nematodes. While most nematodes in soil are actually beneficial, farmers are most concerned with nematodes that are pathogens of the roots, stems, leaves or seeds of plants. Only about 10% of all nematode species are plant parasites, however. Most are freeliving species that feed on other organisms in marine sediments (50%) or nematodes in freshwater sediments or soil (25%). The remaining 15% are parasites of animals or man.

Plant pathogenic nematodes are responsible for over $100 billion in annual crop losses worldwide and over $6 billion/year in the United States. Oregon agriculture, collectively, spends over $11 million/year on nematicides to control nematodes. Additional losses to grower revenues occur from:

1) sampling costs to determine if treatment is necessary,

2) yield losses in crops which are not treated due to grower decisions or the lack of a registered nematicide, or where treatment does not fully compensate for nematode damage,

3) loss in revenue when land must be rotated out of  a high cash value crop to a less profitable crop to reduce nematode populations and/or avoid nematode damage.

While substantial yield increases have been realized with the discovery and use of nematicides, considerable work remains to be done in many aspects of nematode biology and management. On the average, only 0.2% of the value of crop loss due to nematode damage is being invested into nematode research. Furthermore, Nematology is a relatively young science (the first textbook in the United States was not published until 1961), and, although many crops suffer losses due to nematodes, there is rarely more than one field research nematologist per state. Therefore, much remains to be learned to manage these serious pests.