** IMPACT **

University of California,
Div. of Agriculture & Natural Resources
---University Pest Management Guidelines---

WARNING ON THE USE OF PESTICIDES

Pesticides are poisonous. Follow all precautions and recommendations on the pesticide label. The grower is legally responsible for residues on treated crops. Keep all pesticides out of the reach of children, unauthorized persons, pets and livestock. Consult your County Agricultural Commissioner for correct methods of disposing of unwanted pesticides and containers.

COMMODITY: ONION-AND-GARLIC

Record number: 584200111
REVIEWED: 03/93

NEMATODES:
Common Name: Stem and bulb
Scientific Name: Ditylenchus dipsaci

Common Name: Root knot
Scientific Name: Meloidogyne hapla, M. incognita, M. javanica, and M. chitwoodi

Common Name: Stubby root
Scientific Name: Paratrichodorus sp.

DESCRIPTION OF THE PESTS:

Plant parasitic nematodes are microscopic roundworms that live in soil and plant tissues and feed on plants by puncturing and sucking the cell contents with a needlelike mouthpart called a stylet. The stem and bulb nematode lives within the plant, feeding in stems, leaves, and bulbs. It is capable of living without water and tolerates desiccation for several years. Root knot nematodes live within the roots; the second stage juveniles are motile and the other stages are sedentary. Stubby root nematode lives in the soil and feeds on the roots. Lesion nematode, Pratylenchus penetrans, has been reported on onion and garlic in other states where it suppresses the growth and yield of these crops. While this nematode is found in California, it has not been found to cause problems on onions or garlic.

DAMAGE:

Stem and bulb nematode and root knot nematodes cause substantial damage and are of major concern in California. Stem and bulb nematode penetrates the germinating clove and destroys tissue as it moves through seeking food. Nematodes sucking the cell contents and salivary secretions cause the cells to collapse. Root knot nematodes can cause stunting and reduce a stand. Stubby root nematode causes stunting of plants.

SYMPTOMS:

The symptoms described below may be an indication of a nematode problem, but are not diagnostic as they could result from other causes as well. Plants infested with the stem and bulb nematode have distorted and bloated tissues with a spongy appearance; the plants are stunted with shortened and thickened leaves, often with brown or yellowish spots. The bulb tissue begins softening at the neck and gradually proceeds downwards; the scales appear pale gray, and the bulbs desiccate and split at the base under dry conditions. Under moist conditions, secondary invaders such as bacteria, fungi, and onion maggots induce soft rot and decay of the bulbs. Root knot infestation can cause stunting, uneven stands of plants, and produces characteristic galls on roots. Galls induced by M. hapla are generally small and difficult to see, whereas, galls produced by the other root knot species are larger. Roots fed on by stubby root nematode are extremely short with a yellow to brownish cast.

FIELD EVALUATION:

It is critical to know the nematode species present and their population densities to make management decisions. If a previous field or crop had problems caused by nematodes that are also listed as pests of onion or garlic, populations of these nematodes may be high enough to cause damage to seedlings. If nematode species have not previously been identified, take soil samples and send them to a diagnostic laboratory for identification. Divide the field into sampling blocks of between 5 and 20 acres each that are representative of cropping history, crop injury, or soil texture. Be sure to sample the soil from within the root zone (6 to 18 inches deep) and include samples of suspect plants. 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 samples from each block 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. 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: Determine the cropping history of fields to be planted to seed garlic, onion transplants, or onion sets. If the field is not known to be infested with nematode pests of onion and garlic, make sure clean, uninfested cloves are used when planting garlic. Garlic cloves can be tested by private laboratories or the California Department of Food and Agriculture to determine if they are infested. Growing nonhost crops such as carrots and lettuce for several years is helpful in reducing populations of stem and bulb nematodes, but is not usually feasible in fields with root knot and stubby root nematodes because of their wide host range. Avoid infesting new fields by cleaning machinery and equipment with water, and preventing movement of infested soil.

Resistant cultivars: There are currently no resistant cultivars available.

Chemical: Treating bulbs with hot water has been shown to eradicate nematodes from garlic cloves. In the past, a mixture of formalin and hot water was used, but formalin is no longer produced. Research is currently underway to find a replacement for formalin; contact your local farm advisor for the most recent information.

TREATMENT:

Preplant

A. Pesticide (commercial name): METAM SODIUM (Vapam, Soil Prep, Sectagon II)

Amount to Use: 60-100 gal/acre
COMMENTS: Also shown to control bulb mite. Contact your farm advisor for advice on the most effective application method for a particular situation.

Postplant

A. Pesticide (commercial name): FENAMIPHOS* (Nemacur 15G)

Amount to Use: 9.2-18.4 oz for any row spacing. 15-30 lb/acre on 40 inch beds
COMMENTS: For stem and bulb nematode on garlic only. Apply in-furrow with garlic cloves at planting. For best results apply within 7-10 days after cracking.

B. Pesticide (commercial name): OXAMYL* (Vydate L)

Amount to Use: 2-4 qt/acre
COMMENTS: For stubby root and stem and bulb nematode only. Can be applied in-furrow, as a band, or in sprinkler or furrow irrigation. In-furrow and band applications must be followed by irrigation. This is a 24 C registration. See label for additional information.
* Permit required from county agricultural commissioner for purchase or use.

REFERENCE:

Onion and Garlic Pest Management Guidelines. R.M. Davis, F.F. Laemmlen, R.E. Voss. March 1993 PUBLICATION: UCPMG26