How to Manage Pests

UC Pest Management Guidelines

The sheath nematode is less widespread than the citrus nematode; it has been found on citrus in the Coachella Valley and on some native desert plants. However, it has a broad host range and thrives well at high temperatures and at low moisture levels.

DAMAGE
Damage caused by a citrus nematode infestation depends on the age and vigor of the tree, density of the nematode population, and susceptibility of the rootstock. Mature trees can tolerate a considerable number of these nematodes before showing lack of vigor and decline symptoms. In heavily infested sites, young trees may be stunted or fruit production may be reduced on bearing trees that have susceptible rootstocks. The damage is greater when trees are predisposed by other factors such as Phytophthora root rot and water stress.

Sheath nematodes feed on root tips, and may reduce root growth and vigor of trees.

SYMPTOMS
The symptoms described below are typical of a nematode problem but are not diagnostic, as they could result from other causes as well. Aboveground symptoms of nematode damage are lack of vigor, twig dieback, decline in growth, and reduced fruit size and yield. Nematode infestations may occur without inducing any aboveground symptoms. Belowground symptoms of citrus nematode infestation include poor growth of feeder roots and soil adhering to roots giving them a dirty appearance. Sheath nematode causes swelling (galling) of root tips.

FIELD EVALUATION
To make management decisions, it is essential to know the nematode species present and their population estimates. If a previous orchard or crop had problems caused by nematodes that are also listed as pests of citrus, population levels may be high enough to cause damage to the ensuing citrus crop. If nematode species have not previously been identified, take soil samples and send them to a diagnostic laboratory for identification.

Take soil samples within the root zone (6-36 inch depth, depending on soil type). Take subsamples from the regularly wetted zones at the edge of the tree canopy, and include some feeder roots when possible. In drip irrigated orchards, take samples around emitters where feeder roots are abundant. 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 gently and 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. (See UC ANR Publication 3303, Integrated Pest Management for Citrus, 2nd edition, for more details). Keep samples cool (40° to 50°F, 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. Good sanitation practices are essential to avoid nematode infestations. Use certified nematode-free material for planting. Rotation with annual crops for 1 to 3 years before replanting citrus helps to reduce citrus nematode populations.

Rootstock selection. Using a resistant rootstock is recommended whether or not nematodes are present. Trifoliate orange is known to be tolerant to citrus nematode. Troyer citrange is also resistant to citrus nematode, but this nematode has resistance-breaking biotypes that may develop on this rootstock after a period of time, thus increasing its susceptibility. Sweet orange, Trifoliate orange, grapefruit, Thompson seedless grape, and cotton are reported to be resistant to sheath nematode, making its management relatively easy.

Chemical. If the site was previously infested with nematode pests of citrus, preplant fumigation may be necessary to reduce nematode population levels. When replanting a citrus orchard, a preplant treatment is recommended even if a resistant rootstock is used. Trees planted on fumigated orchard sites are generally known to have improved growth and yields compared to those on nonfumigated sites.

In established orchards, treat when sampling indicates more than 400 female citrus nematodes are present in 1 gram of roots in February to April or more than 700 in 1 gram of roots during May and June.

Common name
(trade name)		Amount/Acre
	PREPLANT
A.	METHYL BROMIDE*	300-600 lb
	COMMENTS: Use the higher rates for fine textured soils. Apply methyl bromide in a broadcast fumigation using tarps, or fumigate the soil with 300 lb/acre, invert the top 12 inches of soil, and refumigate in 14 days with 150 lb/acre. A broad-spectrum material that controls weeds, soil fungi, soil insects, and nematodes as well as old roots.
B.	METAM SODIUM*	75 gal
	(Vapam, Sectagon)
	COMMENTS: Metam sodium can effectively control nematodes if applied properly, but it does not penetrate plant roots below 3 ft deep and it is difficult to deliver 4-5 feet down from the surface. Before applying this material, thoroughly cultivate the area to be treated to break up clods and deeply loosen the soil. After cultivation and about 1 week before treatment, preirrigate the field with 6-8 acre-inches of water in flood irrigation in basins. When metam sodium is applied, uniformly add it at 75 gal/acre to 6-8 acre-inches of water. After treatment, do not plant for 30 days, or 60 days if soil is high in organic matter or cold (below 50°F). A broad-spectrum material that controls weeds, soil fungi, and soil insects as well as nematodes.
C,	DICHLOROPROPENE*
	(Telone II)	Label rate
	COMMENTS: See label for application procedures. The soil must be dried for this product to effectively disperse into the soil profile.
	POSTPLANT
A.	OXAMYL*
	(Vydate L)	1-4 qt
	COMMENTS: Apply by metering into flood irrigation water or into drip irrigation systems. Do not apply more than 4 qt/acre in any 30-day period. See product label for additional information on use. Seven day preharvest interval.
B.	FENAMIPHOS
	(Nemacur 3)	2 gal/season
	COMMENTS: Inject into the irrigation system; follow label directions. Do not apply to kumquat, tangelo, or citrus hybrids (see label). Do not apply within 30 days of harvest. Use of this product will be suspended in 2005.

*	Permit required from county agricultural commissioner for purchase or use.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Nematodes
J. O. Becker, Nematology, UC Riverside
B. B. Westerdahl, Nematology, UC Davis
Acknowledgments for contributions to the nematode section:
U. C. Kodira, Plant Pathology, UC Davis

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