How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Nematodes are microscopic roundworms that live in soil and plant tissues. Plant parasitic nematodes feed on plants by puncturing cells and sucking their contents with a needlelike mouthpart called a stylet. They have a wide host range, vary in their environmental requirements, and in the symptoms they cause.

DAMAGE

Root knot nematodes can cause substantial damage to cucurbits. All cucurbits are susceptible to root knot nematodes. Damage is typically greatest in warm regions with light, sandy soils. Nematode-infested plants may have reduced growth, lower yield and fruit quality, and tend to wilt earlier under moisture stress. Lesion nematodes have not been found to cause economic damage in California, but the root lesions formed by their feeding may be invaded by fungi and bacteria. Stubby root nematode can reduce root growth. Pin nematode, Paratylenchus sp., is found in fields but is not known to cause damage to cucurbits in California. Needle nematode has been found to cause damage to cucurbits in the Imperial Valley.

SYMPTOMS

The symptoms described below may be indications of a nematode problem, but are not diagnostic as they could result from other causes such as diseases, insect injury, or nutrient deficiencies. Infestations by root knot nematodes produce characteristic swelling of roots, called galls. Aboveground symptoms for all nematodes include patches of stunted, yellowed, and/or wilted, dying plants. Lesion nematode infestation may cause reddish brown to dark brown lesions on roots. Symptoms due to stubby root nematode infestation include restricted root growth with reduced feeder roots, stunting, and yellowing of plants. Needle nematode causes stunting, terminal root swelling, cessation of root elongation, and root necrosis.

FIELD EVALUATION

It is critical to know the nematode species present and their population estimates to make management decisions. If a previous field or crop had problems caused by nematodes that are listed as pests of cucurbits, population levels may be high enough to cause damage to seedlings. If nematode species have not previously been identified, soil samples should be taken and sent to a diagnostic laboratory for identification.

Soil samples should be taken from within the root zone (6 to 18 inches deep). Divide the field into sampling blocks of not more than 5 acres each, that are representative of cropping history, crop injury, or soil texture. Take several subsamples randomly from a block, mix them thoroughly, and make a composite sample of about 1 quart (1 liter) for each block. Place the samples in separate plastic bags, seal them, and place a label on the outside with your name, address, location, and the current/previous crop and the crop you intend to grow. If plants with symptoms are available, place the roots in the same bag with the soil. Keep samples cool (do not freeze), and transport as soon as possible to a diagnostic laboratory. Contact your farm advisor for more details about sampling, to help you find a laboratory for extracting and identifying nematodes, and for help in interpreting sample results.

MANAGEMENT
Cultural practices. Rotation with nonhost crops can reduce nematode population levels, but it is difficult because of the wide host range of root knot nematodes. Deep plowing, fallow, and destruction of susceptible weed hosts can reduce nematode population levels. Proper irrigation and nutrition reduces stress and may minimize nematode damage.

Resistant cultivars. None available.

Monitoring and treatment decisions.
There are no current treatment guidelines for lesion, stubby root or needle nematodes, but if root knot nematodes are present, treat.

PUBLICATION

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Nematodes
B. B. Westerdahl, Nematology, UC Davis
J. O. Becker, Nematology, UC Riverside
Acknowledgment for contributions to the nematode section:
U. C. Kodira, Nematology, UC Davis

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