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.
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.
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.
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.
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.
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.
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
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
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
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.
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.
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.
Pathogen (fungus) - Erisiphe polygoni
Occurs to some degree annually wherever sugarbeets are grown in the
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 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
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.
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.
Ramularia rarely requires control
measures. In England chemicals have been used to control the disease.
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.
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).
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.
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.
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
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.
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.
Pathogen (fungus)- Fusarium oxysporum Schlecht. F. sp. Betae Snyd.
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.
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.
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.
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
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
Rhizoctonia solani also attacks sugarbeet in the seedling stage,
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.
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.
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
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.
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.
Scientific names: Spodoptera exigua (Beet armyworm); Spodoptera
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
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
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.
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
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.
There are no symptoms of infestation, other than those resulting from
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.
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.
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.
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.
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.
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
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
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
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.
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
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.
Lygus bugs cause injury to the plant by puncturing leaf surfaces and
sucking plant juice from new leaves. Injured plants will wilt and turn
Destroy over-wintered sites including ditches, fencerows and roadsides
to reduce populations. Some insecticides are available in the U.S.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.