Vegetables









Beta vulgaris
Beet
Leaf 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.

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.

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.

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.


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.


Root Diseases
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.

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.

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.

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.

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.


Pests

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.

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.

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.

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.

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.



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.

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.

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.

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.