|Stem and Bulb Nematode||Classification||Hosts|
|Morphology and Anatomy||Life Cycle|
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|Nematode is 1.0-1.3 mm long.
Stylet very short.
Glandular region of esophagus abutting intestine.
Female monovarial, prodelphic.
Races or biotypes are morphologically similar.
Cosmopolitan, especially in temperate regions where it is one of the most devastating plant parasites.
In the western US, nematode populations can be dispersed by annual transport and migration of sheep from Colorado and Utah, although the nematode does not appear to pass through the gut alive. Probably also associated with hay moved with sheep.
Sources of infestation
Spread to new areas
Spread within fields
C-rated pests in California.
Nematode is a migratory endoparasite.
At the beginning of the crop season, 4th-stage juvenile enters young tissues, especially seedlings when below the soil surface.
Feeding breaks down middle lamellae; nematode probably secretes a pectinase enzyme; plant parts become "crisp" and are easily broken.
Migration on plant parts above ground requires free water, and may occur after rain or sprinkler irrigation in alfalfa.
Nematode enters through stomata or by direct penetration.
Over 450 hosts for genus, but 8-10 host races or biotypes, some with limited host range.
Oat race: polyphagous on cereals, most grains, rye, corn, and oats.
Alfalfa race: rather specific on certain legumes, but alfalfa, many weeds, clovers.
Bulb race: most bulbs, daffodil, narcissus, and tulip.
Other hosts of D. dipsaci include onion, garlic, carrots, peas, potatoes, strawberry, sugarbeets; apples and peaches in nurseries; weeds.
For an extensive list of host plant species and their susceptibility, copy the name
select Nemabase and paste the name in the Genus and species box
Monovarial, prodelphic, sexually reproducing.
Life cycle is 19-23 days at 15 C.
Nematodes live 45-75 days when sexually mature; females each produce 200-500 eggs.
Fourth stage juvenile (J4) is survival stage; it can enter a state of cryptobiosis (literally "hidden life") on or below surface of plant tissue - "eelworm wool" - 3-5 years survival (up to 23 years in museum specimens). Survives in soil without host for as long as 2 years, probably feeding on fungi.
Plants become distorted and stunted; infected tissues are spongy; damage can
predispose plants to other problems.
Infestation occurs readily in heavier soils and during times of high rainfall or in sprinkler-irrigated areas.
Field shows irregular areas of sparse growth.
Clover and alfalfa show reduction of internode length and swollen stems.
Nematode is spread around field by equipment, irrigation; spreads readily in tail water.
Stand reductions up to 50% following high fall populations.
Predisposes alfalfa to Phytophthora megasperma.
Bean seed infected with Ditylenchus dipsaci
Bloated, twisted, swollen leaves, distorted and cracked bulbs.
In garlic, infestation can become epidemic.
The nematode was introduced into Venezuela in Mexican varieties of garlic; up to 90% crop loss can occur.
Cloves are infected through to the center where leaf primordia are located; therefore, treatment is difficult without affecting germination.
In 1999, growers in Kern County, California, bought garlic "seed" (cloves) from a nursery in Nevada. The seed had not been heat treated because the nursery had not seen stem nematode in several years.. The growers sustained devastating crop losses and the nursery was sued for $25 million. The nursery had liability insurance through a large company but that company sold the policies to several smaller companies. As of November 1999, the smaller companies were demanding that every field from which losses were reported be sampled to demonstrate the presence of D. dipsaci. That proved possible since there was garlic plant residue present in all the fields.
|Extra tillers, swollen leaf bases.
Photograph of symptoms on winter Barley by Chris Hogger (Switzerland).
Leaves distorted, yellowish swelling (Dutch call it "Spikkels"- see symptoms on garlic leaves), bulbs with dark rings.
In some plant species, inflorescence becomes infested, and pests are spread in the seed, e.g., beans, clover, and alfalfa; infestation can also be spread by infected bulbs.
Photographs by Chris Hogger, Switzerland. Effect of Ditylenchus dipsaci on growth (left), tap-root rot (above).
Ditylenchus dipsaci on sugarbeets in Germany (right), from Dr.
Extracts from correspondence with Dr. Sikora, University of Bonn, April 2003:
"We have a very serious problem in the Rhineland with the stem nematode on sugar beet.... the "Rübenkopfnematoden". ....... This is a unique problem that is now limited to Germany and Switzerland. We have lost all our nematicides and this is the main reason for it popping up so quickly.
Losses can reach a level in which the total field is plowed under. The nematode is reproducing in the beets after harvest and moving through the piles of beets at the factories. The farmers and sugar beet factories are in an uproar. No one has worked on it here in Europe for ages."
|Ditylenchus dipsaci has only been reported as a tobacco
pest in Holland, France, Germany and Switzerland. In those areas
it causes a disease called "stem break".
The problem is not reported from other tobacco producing regions of the world.
Symptoms of stem break include small yellow galls on the stem. The galls increase in size and number and the galled tissue dies. The stem becomes blackened and finally breaks. Younger plants are more severely damaged than older plants (Lucas, 1986).
Hot-water treatment effective for dormant bulbs - narcissus - 44-45 C for 3 hours, but may be ineffective for many other crops.
Hot water harmful to tulips, so cold water with addition of pesticide (e.g., thionazin) is recommended.
Hot water can be used for onions and garlic; formalin no longer used (banned), so Dr Westerdahl and others are refining procedures - see label.
Also, water immersion of garlic cloves activates nematodes, which emerge; then follow with gutathion treatment - cost effective.
Systemic insecticides applied at very low rates (1 lb/acre) are also effective.
Resistant alfalfa varieties include Washoe, Lahontan and Archer (Hafez, 1998).
In Europe, resistant varieties of cereals are grown.
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name
select Nemabase Resistance Search and paste the name in the Genus and species box
Soil fumigation is usually not economical.
Quarantines have been required in England and Holland to control spread of infestation.
Hafez, S. 1998. Fighting nematodes in alfalfa. UC Davis Symposium.
Lucas, G.B. 1986. Plant-parasitic nematodes that attack tobacco. In Plant-Parasitic Nematodes of Bananas, Citrus, Coffee, Grapes and Tobacco. Union Carbide Agricultural Products Inc.