Alfalfa Stem Nematode
Alfalfa Stem Nematode
The alfalfa stem nematode (Ditylenchus dipsaci
(Kuhn) Filipjev), also known at the bulb and stem nematode, occurs
in almost every alfalfa growing region of the world and is considered
the most serious nematode problem on this crop. Infection is
most common in areas that receive heavy rain or irrigation and
is more severe when fields contain heavy soil. Once the nematode
becomes established it can severely limit the productivity of
the field in two to three years. The species is divided into
at least 20 biological races that together are capable of infecting
over 300 plant species. The race that infects alfalfa has several
other hosts that it can survive on but it only reproduces on alfalfa
and sainfoin seedlings. Infection is most common in areas that
receive heavy rain or irrigation and in fields with heavy soils.
The life cycle of D. dipsaci is divided into 6 stages:
egg, four larval stages and adult. All stages except the egg
and 1st stage larva (which molts in the egg) are capable
of infecting susceptible hosts. The nematode survives between
crops as larvae in infested dry hay, alfalfa crown, in soil and
in infested seed lots. Longevity varies and depends on suitability
of the host and environmental conditions. Some fourth stage larvae
can survive many years in dry soil in an anhydrobiotic state.
Survival of dormant larvae in infested seed my last as long
as 20 years. Stem nematodes are spread in infested soil and plant
material by machinery and animals and by rain and irrigation water,
including waste water reapplied for irrigation. The nematode
invades alfalfa plants through the primordial bud then migrates
to other buds. At this stage of infection enzymes produced by
the nematode combined with auxin imbalances in the plant cause
nodes to swell and the internodal region fails to elongate. Migration
continues into the crown area and from here may move down into
roots. Severely infected crowns may die or be subject to winter
kill. Nematodes may also migrate up the plant feeding on leaves
and entering the inflorescence which results in infestation of
seed. A characteristic known only in this species of nematode
is its habit of congregating in large numbers on infested tissue.
The mass of nematodes is referred to as "nema wool".
The presence of stem nematodes and the damage they cause also
serves to predispose the plants to Fusarium and bacterial wilt
and they have been identified as a vector of the latter.
Disease Cycle
Symptoms
A wide variety of symptoms are associated with
stem nematode infestation due to the number of plant tissues affected.
The symptoms are usually seen on scattered plants throughout
the field. The most common symptom observed are plants with swollen
nodes. These plants are stunted and appear bushy, a result of
the shorted internodal area. Infected stems are also discolored.
Lightly infected stems may grow normally. In either case, prolonged
infestation and multiplication of the nematode may result in stem
discoloration that extends from the crown up as high as four inches.
Infected crowns are also swollen, discolored and spongy and produce
few stems. Root infections are characterized by the presence
of internal cavities. Structures resembling galls may form on
the root and girdle the crown. Infected leaves may be curled,
distorted or white. The bleached leaves occur when chloroplasts
are destroyed and the symptom is referred to as white flagging.
Plant Health Management
Plant resistant cultivars
Crop Rotation
small grains , beans and corn are non-hosts
Fall burning
This decreases the population; in contrast, spring burning enhances infection ;
however,we are reticent to recommend burning as an integral Plant Health management tool.
References
Nyvall, R.F. 1989. Field crop diseases handbook,
2nd ed. Van Nostrand Reinhold. New York, NY. 817 pp.
Roth, D. and F. Gray. 1981. Alfalfa stem nematode.
Agricultural Extension Service, Univ. of Wyoming. B-761.
Stuteville, D.L. and D.C. Erwin, eds. 1990.
Compendium of alfalfa diseases, 2nd ed. American Phytopathological
Society. St. Paul, MN. 84 pp.
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Caveat
This description is presented for information only and no endorsement is intended for
products listed, nor criticism meant for products not mentioned. Always consult the product
label before purchasing and using any pesticide.
Material contained on the Links from the page are the responsibility of the linked page's author(s).
This page was drafted by:
Jane Christensen,
Department of Plant Pathology, University of Nebraska-Lincoln
Disease images were provided by:
Dr. David Wysong,
Department of Plant Pathology, University of Nebraska-Lincoln
Questions, Comments, Complaints and Complements?
This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln
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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.
