|
COMMON
SUGARBEET DISEASES AND PESTS
Betaseed's
research team is dedicated to developing varieties that provide
acceptable disease and pest tolerance levels. To learn about
common diseases and pests, click on the topics from below.
Erwinia
Soft Rot
Also known as - Bacterial Vascular Necrosis
Pathogen (bacteria)- Erwinia Carotovora
Erwinia root rot, also known as Bacteria Vascular Necrosis, is
most destructive in warmer growing areas of the U.S. It has been
a production-limiting factor in California and has also been
frequently found in Idaho and Washington.
Symptoms
The disease is not easy to detect until the rot is well
advanced. The vascular tissue of the root becomes discolored and
a pinkish to red-brown rot develops. Root symptoms vary from a
soft rot to a dry rot; the root may become hollow without dying.
As the disease progresses, plants wilt. Occasionally brown,
oozing lesions occur on the petioles and crown, with a froth
developing from the centers of the crowns.
Erwinia root rot can cause serious damage. Disease potential is
greatest when temperatures are in the range of 77° to 86°F
(25° to 30°C). The bacterium is soil borne and plants become
infected when infested soil is moved into the beet crown by farm
machinery, splashing water, insects, or other means. It invades
the plant through an injury or wound to the crown or leaves
where it enters the vascular vessels of the root and petioles.
Control
The most effective means of control is the use of tolerant
varieties. Avoid throwing soil and plant debris into beet crowns
during cultivation, and adjust implements to minimize injury to
crown and tops. Betaseed's Kimberly research team has conducted
Erwinia research and has identified germplasm with resistance.
Varieties tolerant to this disease are available from Betaseed.
Aphanomyces
Also known as - Black Root
Pathogen (fungus) - Aphanomyces cochlioides
This disease occurs in two phases: An acute seedling blight soon
after emergence, and a more chronic root rot occurring from late
June to the end of the growing season. This disease is most
common in the North Central region of the United States,
especially Minnesota and North Dakota, where millions of dollars
of damage can occur annually.
Symptoms
Infected seedlings show blackened, constricted roots generally
followed by plant death. In the chronic root rot, leaves often
become yellow with subsequent wilting. Lateral rootlets are
produced in abundance, many appearing shriveled, black and
necrotic. High soil moisture favors zoospore production and
migration through the soil. Disease development is favored by
fairly high soil temperatures (72-82°F).
Control
The use of a fungicidal seed treatment can reduce disease
severity at the seedling stage. Recommended control measures for
late season chronic effects include rotation with crops other
than sugarbeet; a well-drained, friable soil; control of weed
hosts; and tolerant varieties. Betaseed has a large breeding
program for tolerant varieties based at Shakopee, Minnesota.
There, a virulent and uniform Aphanomyces infection allows
selection and characterization of thousands of sugarbeet parents
and hybrids each year. Sugarbeet varieties tolerant to
Aphanomyces are now available to growers in affected areas.
Cercospora
Leaf Spot
Pathogen (fungus) - Cercospora beticola
In the United States, this fungal disease can occur wherever
sugarbeets are grown but is most prevalent in the central
growing areas from Michigan to Colorado.
Symptoms
Individual leaf spots are nearly circular, measuring 3-5 mm in
diameter at maturity. The lesions are tan to light brown with
dark brown to reddish purple borders. As the disease progresses,
individual spots fuse. Heavily infected leaves first become
yellow and eventually turn brown and necrotic. Blighted leaves
soon collapse and fall to the ground but remain attached to the
crown. Heart leaves are usually less severely affected and
remain green. Cercospora leaf spot is favored by high
temperatures and protracted periods of high humidity or free
moisture on the leaves. Optimum conditions for sporulation,
germination and leaf penetration are temperatures of 77-95°F
with night temperatures above 65°F.
Control
Fungicides are available, but must be used cautiously. The
pathogen appears to become "resistant" to various
fungicides after a few years of heavy and continuous use.
Fungicides with different chemistry should be used in
alternation. Sugarbeet varieties highly tolerant to Cercospora
leaf spot are available from Betaseed. Betaseed has a large
breeding program for tolerant varieties based in Minnesota. Each
year, thousands of current and new lines and hybrids are
artificially inoculated with a myriad of infective Cercospora
spores. The ensuing infection allows separation of varieties
into a range of tolerance levels, from very tolerant to very
susceptible.
Powdery
Mildew
Pathogen (fungus) - Erisiphe polygoni
Occurs to some degree annually wherever sugarbeets are grown in
the United States.
Symptoms
When field-grown sugarbeet plants are two to six months old,
mildew first appears as small, white, powdery spots that appear
usually on the under surface of older leaves. Under suitable
conditions, the fungus spreads rapidly over the entire surface
of the leaf, and eventually the leaf dies. The fungus over
winters on sugarbeet and other Beta species such as Swiss chard,
table beet and wild Beta species that grow throughout the
southwestern United States as mycelium or haustoria in crowns.
Sugar beet powdery mildew occurs annually in March or April on
fall-planted crops in the warm, dry inland valleys of southern
California. Fungal growth and disease development is strongly
influenced by light, temperature, and relative humidity. The
optimum temperature for disease development is 77°F,
with limits of 59°
and 86°F.
Control
Control is through the use of suitable fungicides and/or
tolerant varieties. Under normal field conditions the Kimberly
research staff evaluates lines and hybrids in fields highly
affected by powdery mildew. Betaseed has been successful in
developing varieties with moderate to good resistance to this
disease. Chemical control measures are often used in combination
with moderately resistant varieties. If fungicides are used,
they should be applied when the first small, white powdery spots
appear on the undersurface of leaves. Repeated applications are
necessary at 3 to 6 week intervals if the disease reappears.
Rhizoctonia
Root and Crown Rot - common name
Pathogen (fungus) - Rhizoctonia solani
Rhizoctonia root and crown rot, caused by a soilborne fungus, is
one of the most common and widespread root diseases of sugarbeet
in the United States.
Symptoms
Above ground symptoms on older plants include sudden wilting and
yellowing of foliage and black rotting of petioles near the
crown. Wilted leaves subsequently collapse and die, forming a
dry, brown or black rosette, which persists through the growing
season. Exposed areas of infected roots are often covered with
masses of brown mycelium. The fungus causes a characteristic dry
rot that is brown with deep fissures at or near the crown. The
root and crown are partially or completely destroyed.
Rhizoctonia solani also attacks sugarbeet in the seedling
stage, causing damping-off.
The fungus is widespread, has many crop hosts, and survives on
plant debris in the soil as small, resting structures called
sclerotia. This disease is most common during spring and summer
when conditions are warm (77°
to 92°F, 25°
to 33°C) and
soils are moist. The fungus grows through the soil and infects
the root and crown of plants. Rhizoctonia occurs in most soil
types but is most severe in heavy, poorly drained soil where
water collects.
Control
Recommended control measures include tillage and fertilization
that promote good crop growth and adequate soil drainage.
Sugarbeet should be planted in rotation with corn or small
grains, and when cultivating, avoid throwing dirt into the
crowns of the plants. Sugarbeet varieties with enhanced
tolerance to Rhizoctonia have recently been developed and are
available to growers. At Betaseed's Kimberly, ID facility,
artificially induced conditions are used to screen all lines and
hybrids for resistance to Rhizoctonia. Betaseed has been very
successful with developing tolerant varieties to combat this
disease.
Yellowing
Viruses
Pathogens - Beet Yellows Virus (BYV), Beet western yellows virus
(BWYV), and Beet mosaic virus (BtMV)
Although beet-yellowing diseases may occur in many
sugarbeet-growing areas, the greatest losses have generally been
experienced in California.
Symptoms
Symptoms of beet yellows virus and beet western yellows virus
are very similar and typically first appear on older leaves that
begin to yellow in the area between the veins where small
reddish brown spots often appear, giving the leaves a distinct
bronze cast. Eventually leaves become thick, leathery, and
brittle. Severe strains of beet yellows virus first cause a vein
etching of the heartleaves followed by yellowing of entire leaf
blades or sectors of older leaves. Beet mosaic virus infects
young leaves first. These leaves show a mosaic or mottled
pattern that may disappear as the leaves mature.
These diseases are vectored primarily by the green peach aphid, Myzus
persicae, and the black bean aphid, Aphis fabae.
Other aphids, including the bird cherry-oat aphid and blue
alfalfa aphid, have been shown to vector beet yellows virus, but
their significance in the spread of the disease is still
unclear. The aphids obtain beet yellows and beet mosaic viruses
primarily from overwintering beets; beet western yellows and
beet chlorosis viruses have a very wide host range, however,
including plants in the crucifer and composite families. Disease
potential is greatest in years when aphids are able to colonize
beets early in spring and multiply rapidly. Crop loss can be
considerable, ranging up to 2% or more per week of infection.
Plants infected at early stages of development suffer the
heaviest losses; late infections (4-6 weeks before harvest) may
not cause significant yield loss.
Control
In California strict planting programs have been implemented
allowing no early spring plantings in or adjacent to growing
districts where sugarbeets were overwintered in the field. In
addition, Betaseed has been successful in developing varieties
with some combined tolerance to Beet Yellows and Beet Western
Yellows.
Rhizomania
Pathogen (Virus) - Beet necrotic yellow vein virus (BNYVV)
Rhizomania is one of the most destructive diseases of sugarbeet.
Rhizomania is endemic to California and Southern Minnesota, is
fairly widespread in Idaho, Colorado, Nebraska and southeast
Wyoming, and has been detected in the Red River Valley of
Minnesota and North Dakota.
The causal agent, beet necrotic yellow vein virus, is
transmitted by the soilborne fungus Polymyxa betae. BNYVV
reproduces only within the living tissue of its host. Disease
development is influenced by the fungus, which is enhanced by
saturated soil conditions from rain, irrigation, or poor soil
drainage. In infested fields, most sugarbeets are affected:
roots are usually small, sugar yields are poor, and losses can
be as high as 100%. Recent studies suggest that additional
losses in fields with infected beets may be the result of
secondary invasion by other root pathogens, such as Phytophthora
or Pythium.
Symptoms
The symptoms of Rhizomania are root stunting and proliferation
of lateral rootlets on the main taproot, giving it a bearded
appearance. The storage root is often rotted and constricted
(turnip-shaped) below the soil level, and vascular rings are
visibly darkened. Leaves can be mildly yellowed and have an
upright posture. Rhizomania is a problem when several conditions
exist simultaneously: Polymyxa betae is present in the
soil; BNYVV is associated with the fungus; soil temperature is
fairly high (over 68°F)
for an extended period of time; the soil has a high moisture
content from abundant rainfall, intensive irrigation, or poor
drainage; and the soil is neutral to slightly alkaline.
Control
The best method of control is the use of Rhizomania resistant
varieties. Betaseed has developed varieties with high levels of
Rhizomania resistance available for most growing areas where the
disease is prevalent. Such varieties generally include
Rhizomania resistance along with tolerance to other endemic
diseases.
Curly
Top
Pathogen (virus) - Beet curly top virus (BCTV)
Beet curly top is a highly destructive disease, which is
widespread throughout the western United States.
Beet curly top virus is vectored by the beet leafhopper, Circulifer
tenellus, which has an extensive host range, a high
reproductive capacity, and can migrate long distances from its
desert breeding to cultivated areas. The leafhopper overwinters
on a wide range of annual and perennial weeds and readily
acquires the virus when it feeds on infected plants. In spring,
it migrates to agricultural lands when the overwintering host
plants dry out. Beet curly top virus also can cause significant
losses in tomatoes, beans, and cucurbits.
Symptoms
Leaves are dwarfed, crinkled, and rolled upward and inward.
Veins on the lower side of infected leaves are roughened and
irregularly swollen with spine-like outgrowths. Roots are
dwarfed, and rootlets tend to become twisted and distorted and
often die.
Control
Curly top is more damaging if plants are infected as they are
young or under stress. Therefore it is important to plant as
early as possible and avoid unnecessary stress. Under moderate
infection pressure, control of leafhoppers via application of
insecticides, can also reduce curly top infection. Resistant
cultivars are also important in the control of curly top. The
Kimberly, ID program includes an extensive curly top testing and
variety development program for curly top resistance. Betaseed
sells many varieties having tolerance to curly top.
Root
Maggot
Scientific name: Tetanops myopaeformis
The sugarbeet root maggot may be the most destructive insect
pest of sugarbeet in the United States. The sugarbeet root
maggot larva is also a small, legless maggot with no distinct
head or eyes. It is white in color and has two dark mouth hooks
at the pointed end used for feeding. The adult fly is about the
size of a housefly with a shiny, black body with brownish spots
at the base of the wings. The sugarbeet root maggot over-winters
as full-grown larvae in previously planted beet fields. Adult
flies emerge in April, May, and June. They migrate to nearby
beet fields and deposit their eggs in the soil around small beet
plants. The eggs hatch in a few days, and the larvae begin to
feed on succulent roots of sugarbeet. The damage to sugarbeet
from this insect is due to the larvae. Sugarbeet root maggot
feed on the roots by scraping the root surface with their mouth
hooks, causing irregular scars, which later become darkened from
sap escaping from the injured root. Their feeding may provide
entry points for soilborne pathogens. The insect thus reduces
beet stands, retards plant growth, and reduces yield. They may
sever taproots of small plants, causing plants to die.
Control
Most growers rely on insecticides incorporated during seed
sowing to control the sugarbeet root maggot. Betaseed initiated
a breeding program for tolerance in 1997. However tolerant
varieties with acceptable quality and yield are not yet
available.
Root
Aphid - common name
Scientific name - Pemphigus populivenae (betae)
The sugarbeet root aphid is one of the most widespread insect
pests of sugarbeet in the United States.
Severe damage to non-tolerant cultivars can occur in Michigan,
Colorado, Nebraska, Wyoming, Montana and other areas. As the
name implies, these aphids are restricted to the roots, and are
generally associated with the fibrous roots rather than the main
storage root. Winged adults migrate from winter hosts
(cottonwood trees, soil) to sugarbeets in early summer and lay
their eggs. They may occasionally be seen in wooly wax masses in
the crown as they crawl up from roots to fly to new hosts. The
wingless aphid progeny reduce both the size and quality of beet
roots by sucking sap from them. They are yellowish in color and
secrete a dull, white waxy substance, giving the root a mealy
appearance. In heavy infestations, beet leaves turn a yellowish
green, with plants wilting and often shrinking in size. Severely
infested plants become chlorotic and wilt easily; under
conditions of prolonged moisture stress, the storage root
becomes flaccid and rubbery. Infestations in the field often
appear as circular or elliptical patches in which the foliage on
plants is wilted or, in extreme cases, collapsed or dying. No
economic thresholds have been established for sugarbeet root
aphid. However, studies in California show that even light to
moderate infestations (less than 10%) can cause serious yield
reductions. Sugar content and purity may be drastically reduced.
Control
Tolerant varieties are widely available. At Shakopee, Minnesota,
Betaseed has a comprehensive breeding and selection program for
root aphid resistance. As a result, most new Betaseed varieties
sold in the affected areas incorporate root aphid tolerance.
Bacterial
Leaf Spot
Causal organism - Pseudomonas syringae van Hall
The beet acts as a host to the bacteria. It may be transmitted
by the seedling and causes seedling blight on young plants. This
disease has been reported in the Western U.S., Ohio and some
foreign countries.
Symptoms
The symptoms of bacterial leaf spot are dark brown to black
streaks and spots on leaf blades with occasional discoloration
on seedstalks and petioles. A plant wound or injury is necessary
in order for the disease to grow. Optimal growing conditions
include a temperature range of 77°-86°F.
Control
There are no known field strategies for controlling this
disease. Some fungicides are successful at treating the disease
during the seedling blight phase. Reduce the incidence of
disease by planting seed that is free of the bacteria.
Black Root
- Common name
Also known as - Aphanomyces
See Aphanomyces disease
information.
Fusarium
Pathogen (fungus)- Fusarium oxysporum Schlecht. F. sp. Betae
Snyd. & Hans.
Fusarium is a root disease caused by a fungus present in the
soil. This disease has been reported in the western areas of the
United States, India and some European countries.
Symptoms
This disease attacks the beet by entering through the root
system and is transported to the leaves via the vascular system
of the plant. The leaves turn yellow, usually starting with the
older leaves, and progressing to the younger leaves. Frequently
only one side of the leaf may show disease symptoms. The fungus
is a soil inhabitant, surviving as spores. Growing successive
sugarbeet crops may potentially cause serious damage to
subsequent beet crops. Additionally the disease favors hot
weather so symptoms rarely appear before July.
Control
Crop rotation is frequently recommended. Additionally, some
tolerant germplasm has been identified. Betaseed has a
successful screening program for Fusarium and has incorporated
tolerance into several varieties.
Armyworms
Scientific names: Spodoptera exigua (Beet armyworm); Spodoptera
praefica Western
yellowstriped armyworm
Armyworms belong to the same family that includes cutworms. Some
of the common species attacking sugarbeet are the armyworm, Psudaletia
unipuncta (Haworth); the beet armyworm, Spodoptera exigua;
the fall armyworm Spodoptera frugiperda; and the western
yellowstriped armyworm Spodoptera praefica. Adult beet
armyworms are small, mottled gray or dusky winged moths. Females
deposit pale greenish or pinkish, striated eggs on leaves in
small or large masses covered with white cottony material. Eggs
hatch in a few days and tiny caterpillars begin feeding on the
plant. When caterpillars are full grown, about 2 to 3 weeks,
they are about 1.25 inches long. The color down the middle of
the back may be olive green to almost black with a yellow stripe
on each side of the body. There is a dark spot on each side of
the thorax just above the middle leg. Beet armyworms may become
abundant and cause severe injury in summer and fall.
Western yellowstriped armyworm may be abundant in fields in the
Central Valley any time from June to early September. The
caterpillar is usually black, with two prominent stripes and
many narrow bright ones on each side. At maturity it is
approximately 1.5 to 2 inches long. They burrow into the soil to
pupate and emerge as adult moths. Others when they reach
adulthood are black and white with stripes or all black. Eggs
are laid in clusters and covered with a gray, cottony material.
Symptoms/Damage
Leaves are damaged by the larvae eating the foliage, mostly at
night. Many armyworms infect sugarbeet fields because their
primary food source, grain fields, has been eliminated or
removed. Armyworms eat leaves, leaving them as skeletons so that
the veins are largely intact. In severe infestations as food
becomes scarce, they will consume the veins, petioles, and will
even feed on the portion of the storage root sticking above
ground.
Control
Recommendations include not planting sugarbeets following small
grains or alfalfa. Natural enemies of the armyworm include
tachinid flies, certain wasp species, and birds. Some
insecticides are approved for use against armyworms. Economic
thresholds have not been established for beet armyworm.
Sugarbeets can sustain considerable defoliation, particularly
late in the season, without resulting yield reductions. Treat
only if natural (biological) pest suppression fails to bring the
population under control.
Ramularia
Leaf Spot - Common name
Causal organism - Ramularia beticola
Ramularia affects sugarbeets and beet fodder primarily in cool,
damp climates. It has been reported in the western U.S., Canada
and Europe.
Symptoms
The fungus typically attacks older leaves. Leaf spots are
usually light brown and approximately 4-7 mm in diameter.
Mature leaf lesions may be reddish-brown with silvery gray or
white centers. Leaves then turn yellow and die. High plant
density combined with a sulfur deficiency increases disease
intensity. The disease favors low temperatures and high
humidity; thus, as soon as warm, dry weather occurs, plants may
recover.
Control
Ramularia rarely requires control measures. In England chemicals
have been used to control the disease.
Cutworms
There are approximately nine species of cutworms that can have
an economic effect on sugarbeet growers. By specie, they vary in
populations and economic impact across the United States.
Symptoms
Most crop damage occurs in the spring when the larvae that have
over-wintered in the soil start eating the plant at or just
below the soil level. Most crop damage is done by
first-generation cutworms with the plants damaged at the base.
Control
Some species are difficult to control as they survive below the
soil. Cultural practices, such as spring plowing and disking,
may reduce the chances of crop damage. Whenever there is a
possible infestation, sugarbeets should not follow small grains
or alfalfa in a crop rotation. Some species have natural enemies
that will prey upon these worms. Also, insecticides are
available in the United States to treat cutworms. Fields should
be kept weed-free, particularly grassy weeds that serve as
alternate hosts for cutworms. Cutworms may also build up in high
numbers if grassy weeds are prevalent in the crop preceding
sugarbeets. Cutworms are attacked by a number of predators,
parasites, and diseases. Many of these natural control agents
are not effective on pale western and black cutworms because of
their subterranean nature. It is not known if any of these
natural enemies can control cutworm populations, but their
presence should be noted. No economic thresholds have been
established for cutworms, and the decision to treat depends on
the severity of injury. Organophosphate and carbamate
insecticides do not control the granulate cutworm.
Leafhopper
Scientific name: Ciculifer tenellus
This pest, which thrives in the semi-arid regions of the western
U.S., is considered one of the most important pests in the
sugarbeet industry. Direct feeding by beet leafhopper causes
relatively minor damage. Its pest status derives from its
transmission of beet curly top virus (BCTV). The beet leafhopper
is approximately 0.125 inches long, wedge shaped, and pale green
to gray or brown in color. It may have dark markings on the
upper surface of the body. It may be distinguished from Empoasca
leafhoppers by its darker markings; Empoasca leafhoppers are a
uniform green color. Beet leafhopper overwinters on rangeland
weeds (mustards, desert plantains and other weeds) and migrates
to sugarbeet and other crops in spring as its overwintering
hosts die.
Symptoms
There are no symptoms of infestation, other than those resulting
from BCTV.
Control
Numerous predators and parasites exist but researchers are
unclear as to the role and control of the leafhopper using these
measures. Insecticides are available in the U.S.
Lygus
Bug
Certain species of Lygus bugs are primarily seed feeders so are
not considered major pests to sugar beets. Some species,
however, are injurious to sugarbeets and can pose a threat to
plant health.
Symptoms
Lygus bugs cause injury to the plant by puncturing leaf surfaces
and sucking plant juice from new leaves. Injured plants will
wilt and turn brown.
Control
Destroy over-wintered sites including ditches, fencerows and
roadsides to reduce populations. Some insecticides are available
in the U.S.
Cyst
Nematode and Root-knot Nematode
Scientific names: Heterodera schachtii and Meloidogyne
arenaria, M. incognita, M. javanica, M. hapla, and M.
chitwoodi. False root-knot: Nacobbus dorsalis
Plant parasitic nematodes are microscopic roundworms that feed
on plant roots. They survive in soil and plant tissues and
several species may exist in a field. They have a wide host
range, vary in their environmental requirements, and in the
symptoms they induce. Apart from the nematodes listed above,
other species, such as stubby root, sting, needle, spiral,
sheath, stem and bulb, and potato rot nematodes, have been
reported as pests on sugarbeet.
Damage
Infestations of sugarbeet cyst nematode may be localized or
spread over an entire field. In heavily infested soils, seedling
emergence may be delayed or seedlings may be killed before
emergence, resulting in a reduced stand. Seedlings infested with
sugarbeet cyst nematodes may be predisposed to secondary
infection by soilborne fungi.
Although other root knot species, such as Meloidogyne hapla,
are widely distributed, Meloidogyne chitwoodi, M. incognita
and M. javanica are the most damaging of root knot
nematode species found in sugarbeet.
Symptoms
Symptoms described below are indicative of a nematode problem,
but are not diagnostic as they could result from other causes as
well. Infestations may occur without causing any aboveground
symptoms.
Seedlings infested by sugarbeet cyst nematode may have longer
petioles than normal, with green or yellow leaves depending on
the severity of infestation. Plants are likely to be stunted and
wilted. Typically, storage roots will not be well developed, and
will have excessive fibrous roots. Mature female nematodes
(cysts) can be seen on the root surface as tiny, pinhead size,
round or lemon-shaped bumps, which are white in the earlier
stages and turn brown on aging.
Heavy infestation by root knot nematodes in sandy soils may
cause plants to wilt and collapse. Swellings (galls) can be seen
on fibrous roots and the taproot, which may have a warty
appearance. Symptoms of false root knot nematode infestation are
similar to those produced by Meloidogyne spp.
Field Evaluation
To make management decisions, it is critical to know the
nematode species present and their population estimates. If a
previous crop had problems caused by nematodes that are also
pests of sugarbeet, population levels may be high enough to
cause damage to an ensuing sugarbeet crop. If nematode species
have not been identified previously, take soil samples and send
them to a diagnostic laboratory for identification.
Before planting sugarbeet, take soil samples from within the
root zone in fall after harvest of the previous crop or
preferably just before harvest. Divide the field into sampling
blocks of 10 to 20 acres 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. Include roots
in the sample if possible. 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. Keep samples cool (do not freeze), and
transport as soon as possible to a diagnostic laboratory.
Management
Crop Rotation. Rotation with non-host crops is widely
used to control sugarbeet cyst nematode. The interval between
sugarbeet and other crops in rotation depends on the severity of
infestation and local conditions influencing the nematode.
Control of root knot nematodes by crop rotation is very
difficult because of their wide host ranges. Nematode-resistant
tomatoes can be grown if Meloidogyne incognita, M. javanica, or
M.arenaria are present.
Planting Date. Planting when soil temperatures are below
50°F for Heterodera schachtii and 65°F for M.
incognita reduces damage and slows nematode population
buildup.
Fallow. Weed-free fallow, which deprives nematodes of
food, reduces most nematode populations. Fallow is most
effective if soil is plowed and exposed to sun. Irrigation
during the dry period further reduces nematode populations if
proper weed control is maintained. The importance of the time of
year in which to fallow as it relates to rate of decline of the
nematode population is not well understood at this time.
Wireworms
Scientific names: Agriotes spp. and Limonius spp.
Wireworms are actually the larvae of click beetles and attack
many different plants, including sugarbeet roots. They are
yellowish brown, thin worms that have a shiny, tough skin.
Adults of the wireworms are click beetles, so named because
their elongated bodies are capable of producing a clicking
sound. Only the larval stage causes damage.
Symptoms
Wireworms may live in the soil for many years and feed on
various plant roots. They have elongated shiny bodies
approximately 13-19 mm long and move quickly in the soil. They
eat the tender roots of seed and seedlings. Wireworms feed on
roots of emerging plants, killing the seedlings and reducing the
stand. As plants mature, wireworms may girdle the stem. Be sure
to dig around the plant and look for wireworm larvae to confirm
that they are the cause of injury. Crop damage is most severe
during cool, moist weather. Wireworms bury themselves in the
soil during hot, dry spells.
Control
Wireworm infestations are difficult to detect before visible
plant injury occurs. They are most likely to be found in a
sugarbeet field when sugarbeet follows a long-term legume crop
or natural or temporary pasture. Crop rotation and deep plowing
of fields may help to reduce wireworm populations. Some
chemicals are approved to treat these pests. Chemical controls
are ineffective or impossible to apply to wireworms attacking a
standing crop. If used, chemicals must be applied as pre-plant
or seed treatments.
Whitefly
Sweet Potato Whitefly
Scientific Names: Silverleaf whitefly - Bemisia argentifolii;
Sweetpotato whitefly - Bemisia tabaci
Description of the Pests
Whitefly adults are tiny (0.06 inch, 1.5 mm long), yellowish
insects with white wings. They are found mostly on the
undersides of leaves. The tiny, oval eggs hatch into a first
larval stage that has legs and antennae, which will be lost
after the first molt. Nymphs are soft, oval, flat and remain
fixed at one feeding site.
Silverleaf whitefly adults immigrating into beet fields may
build up to extremely high numbers on the underside of leaves.
They fly in great clouds when disturbed.
Damage
In the Imperial Valley, silverleaf whiteflies and sweetpotato
whiteflies will feed and deposit eggs on sugarbeets, but the
nymphs do not survive to the adult stage. In high populations,
whiteflies can damage sugarbeet by sucking sap from plants and
causing stunting and wilting. Large populations along with very
hot weather may kill young plants. Whiteflies do not appear to
be a problem in the San Joaquin Valley. While large numbers of
adults may be seen on foliage in fall, especially in sugarbeet
fields adjacent to cotton, they do not lay eggs on sugarbeet
leaves.
The sweetpotato whitefly is a vector of lettuce infectious
yellows virus, an extremely destructive virus of sugarbeet; the
silverleaf whitefly, however, is not. In recent years,
sweetpotato whitefly has been displaced by the silverleaf
whitefly and lettuce infectious yellows is currently not a major
concern. Silverleaf whitefly does inject a toxin into the plant
as it feeds, which causes the leaf petioles to turn white.
Plants recover, however, when whitefly populations decrease with
cooler weather in fall.
Cultural Control
When possible, plant sugarbeets at least 1/2 mile upwind
from key silverleaf whitefly hosts such as melons, cole crops,
and cotton. Maintain good sanitation in areas of winter/spring
host crops and weeds by destroying and removing all crop
residues as soon as possible. Control weeds in non-crop areas
including head rows and fallow fields and harvest alfalfa on as
short a schedule as possible. In addition, allow the maximum
time between whitefly host crops.
Biological Control
Several wasps, including species in the Encarsia
and Eretmocerus genera, parasitize whiteflies. Whitefly
nymphs are also preyed upon by bigeyed bugs, lacewing larvae,
and lady beetles. Silverleaf whitefly is an introduced pest that
has escaped its natural enemies. Some indigenous native
parasites and predators do attack it, but do not keep it below
damaging numbers. The lady beetle Delphastus pusillus is
being introduced into southern California to assist in
biological control.
Monitoring and When to Treat
Routinely check field margins for whiteflies; these areas
are usually infested first. Be especially alert for rapid
population buildup when nearby host crops are in decline. Allow
beneficials an opportunity to control light whitefly
infestations. If higher populations are present at the field
margins than the field centers, then treat only the field
margins. This approach will reduce treatment costs and help
preserve beneficials in the field.
In the Imperial Valley treatment may be necessary in September
if high populations of this pest are immigrating into sugarbeet.
No economic thresholds are established. While good coverage is
essential with oils and soaps, phytotoxicity may be a problem.
Beet
Western Yellows (BWYV) - See yellowing viruses above
Please refer to "Compendium of Beet Diseases and Insects" for further beet disease and pest information.
Phone:
(800) 428-8455
Email: infoseek@betaseed.com
Shakopee,
MN | Kimberly, ID | Disease
Information |
