muskmelons have been reported in Arizona, California, Idaho, and Utah. In 1945, N. J. Giddings, a specialist on The Beet Leaf hopper curly-top virus, found that flax from the San Joaquin Valley, Calif., was infected with curly top. Later tests in- dicated the possibility of serious injury /. R. Douglass, William C. Cook to flax during seasons of high infesta- tions.

The beet leafhopper is the only THE BEET LEAFHOPPER^ commonly known carrier of curly top, a destruc- called the whitefly in the West, is tive virus disease of sugar beets, beets, slightly more than one-eighth inch beans, tomatoes, spinach, melons, other long. It is gray to greenish yellow\ It crops, ornamental flowering plants and is a sun-loving, dry-climate insect and many weeds. The insect favors arid and often breeds on many species of intro- semiarid localities of the western duced weeds established on nonagri- United States, northern Mexico, and cultural and deteriorated range lands. southwestern Canada. Its breeding It feeds by sucking juices from its host grounds are abandoned and overgrazed plants. Rarely does it become numer- lands on which weed hosts occur. Such ous enough to cause great direct dam- areas are also reservoirs for the virus. age by its feeding. It is important then Curly top has been given many com- only because it carries curly top. mon names—on sugar beets it has been The virus of curly top survives the called California beet blight, western winter in both the beet leafhopper and blight, blight, curly leaf, and curly top ; its winter host plants. The leafhopper on tomatoes, tomato blight, yellow transmits it during feeding. It is carried blight, summer blight, western blight, from the winter hosts to other weed w^estern yellow tomato blight, tomato hosts and cultivated susceptible crops, yellows, and tomato curly top; on principally during the spring move- beans, bean blight. ment. Some of the crops in their seed- How serious it can be is shown in ling stage arc very susceptible to the records for southern Idaho, where disease. Infected plants often die. The g;rowcrs of sugar beets in 1924 aban- percentage of the spring-generation doned 11,442 out of 22,418 acres they leafhoppers carr^âng the virus has planted. In 1934 they abandoned 18,- varied from year to year, with a low of 635 out of 21,389 planted acres. The 4 percent and a high of 80 percent. average yields of the harvested fields Varieties of sugar beets that are re- were 5.51 and 4.88 tons an acre for sistant to curly top have been devel- 1924 and 1934—far below the 16-ton oped. We have no commercial varieties average in years of little leafhopper of tomatoes that are resistant. Serious exposure. Factories were dismantled losses occur during years of leafhopper and moved to other places, only to be outbreaks in parts of California, Colo- dismantled and moved again when it rado, Oregon, Utah, and Washington. v/as found that they had been relocated In southern Idaho and some other in areas infested by the beet leafhopper. areas, tomatoes are not grown for com- A leafhopper can pick up the virus mercial use, because the crop is prac- from a diseased plant and transfer it tically a complete loss in years of drastic to a healthy plant in 4 hours. Once a exposure to curly top. leafhopper has become infected with Most varieties of snap beans are sus- the virus of curly top, it remains in- ceptible. Southern Idaho produces ap- fective, but it cannot transmit the virus proximately 80 percent of the national through the eggs to its progeny. requirement of garden seed beans. The Serious losses to cantaloups and area is free from bacterial blight and 544 The Beet Leafhopper 545 other seed-borne bean diseases. During velop typical symptoms of the disease years when large spring movements of and generally grow to maturity. hoppers coincide with the "crookneck," In tomatoes the first reliable symp- or seedling, stage, field after field of the tom is a general drooping, but not wilt- most susceptible varieties of beans in ing, accompanied by yellowing of the southern Idaho have been so seriously young leaves and purpling of the veins. damaged by curly top that it has been The plant is abnormal—often silvery— necessary to plow them under. Losses to in color. The leaves thicken and be- less susceptible varieties have also been come leathery and brittle. The entire high. In the past, serious losses occurred plant turns yellow and usually dies. In in most of the varieties of the field, or seriously diseased plants the blossoms dry, beans. The Idaho Agricultural Ex- may drop and no more fruit is set. periment Station has developed resis- Fruits that are already formed turn yel- tant varieties of Great Northern and lowish red, ripen prematurely, and are pinto beans. stunted and of poor quality. In squash the symptoms are some- THE EARLIEST VISIBLE SYMPTOMS of v/hat similar to those in the other sus- curly top in beets are the clearing of the ceptible commercial crops. If the young tiny veinlets and the inward rolling of seedling is infected by virus-carrying the lower and outer margins of the leaf hopper s as soon as it emerges above youngest leaves. As the disease gets the soil, it may die before its true leaves more severe, the curling and distortion appear. In the older infected plants, of the leaves increase, vein swelling new growth is stunted, internodes are occurs, and. numerous papillae, or shortened, and the leaves may roll up- wartlikc bumps, appear on the under ward at the margins. An upward bend- sides of the leaves. A general stunting ing of the tip of the runner is charac- often ends in the death of the plant in teristic. Blossoms may drop and not the most severe cases. The diseased set fruit, and the fruits already formed leaves are dark, dull-green, thick, crisp, are stunted. There are no distinctive and brittle. The roots show marked color differences by which a diseased symptoms. The disease causes the death plant may be identified. Wilting is not of the lateral rootlets and the beet then characteristic of curly-top infection in sends out a large number of new lateral squash plants. rootlets, which look hairy or woolly. Infected cantaloups show no reliable A cross section of a diseased root often symptoms. Infected seedlings become shows dark concentric rings alternating severely stunted and usually die. In the with light circular areas. A longitudinal older infected plants, new growth is section shows the dark discoloration stunted, internodes are shortened extending lengthwise throughout the tow^ard the end of the runners, and the beet. leaves may become puckered with the In beans the first symptoms are the margins turned down. The flowers be- most pronounced on the trifoliate come dwarfed and often become dry leaves, which become slightly puck- before the petals expand. Yellowing ered, curl downward, turn yellow, and occurs in severe cases. die. They and the primary leaves are Spinach affected by curly top under- thicker than normal and brittle and goes stunting, shows crinkling and break on readily. The infected young curling of the leaves, and acquires a plants soon die. Plants infected later in more leathery texture and, in severe the season may drop their blossoms, cases, yellowing of the leaves. become chlorotic, and die. Affected Considerable variations may occur plants are decidedly dwarfed and have in the symptoms of the infected plants, short internodes, which give them a depending on the strains of the virus. bunchy appearance. Plants infected The length of the incubation period late in the season do not always de- and the severity of the disease that de- 546 Yearbook of Agriculture 1952 velops depend on the age and condition the possibility that new and possibly of the plant, its resistance, virulence of more virulent strains of the virus of the virus, temperature, relative humid- curly top will have to be dealt with. ity, and light intensity. High tempera- Since the beet leafhopper survives ture^ low relative humidity, and high only in a dry climate, it has probably light intensity all increase the severity reached the limits of its economic dis- of the disease and the rate of develop- tribution in North America. The gen- ment. Irrigation does not check the eral climatic condition, rather than its disease. Serious epidemics of curly top host plants, is the limiting factor in re- are dependent on several contributing stricting further geographical distribu- factors—magnitude and time of the tion of this insect, as its summer, win- movement of spring-generation leaf- ter, and spring breeding host plants are hoppers, percentage of leafhoppers found growing abundantly outside of carrying the virus of curly top, size and its economic range. condition of susceptible plants at the In only two instances has the insect time of infection, and weather con- been reported in the Eastern States. ditions. D. M. DeLong found it reproducing The first variety of beets resistant to on purslane sesuvium {Sesuvium por- curly top, U. S. i, was developed by tucastrum) at Miami, Fla., in 1921. the Bureau of Plant Industry, Soils, In 1936 he and K. J. Kadow collected and Agricultural Engineering and was it from horseradish at Gollinsville, 111. released to growers in 1934. Since then, An occasional outbreak of the insect other resistant varieties have been re- and the curly top disease may be ex- leased. Each is an improvement in pected in areas removed from its nor- resistance and adaptation. The devel- mal range. Such outbreaks have oc- opment of varieties of sugar beets resist- curred in the past in the Big Horn ant to curly top has greatly lessened the Basin, Wyo., and near Billings, Mont. losses to the crop. Eubanks Carsner and Those outbreaks evidently followed F. V. Owen have told the story in long-distance migrations of the leaf- Science in Farming, the 1943-1947 hopper into the areas, followed by Yearbook of Agriculture, of the re- favorable weather conditions for the search that made this possible. insect for a few years. Because the The development of resistant varie- disease depends on the vector for its ties of sugar beets has made it profitable spread, it is limited to the region in- to grow beets again in areas of the fested by the beet leafhopper. western part of the United States that are affected by the beet leafhopper. THE BEET LEAFHOPPER passes the Even the resistant varieties are suscep- winter in the adult stage, chiefly in tible to curly top in the early stages of uncultivated and overgrazed areas growth, however, although they are far where mustards or other suitable host more resistant to injury than the non- plants grow. The insects are active and resistant varieties previously grown, feed during the winter whenever the such as Old Type. Although the threat temperature permits. The female de- of failure to the beet crop has been velops its eggs in late winter. Egg-lay- greatly lessened, curly top has not van- ing usually begins about the time the ished, as serious losses from curly top host plants begin spring growth. The have occurred in California, Idaho, eggs are laid inside the tissues of the Nevada, and Utah in recent years when leaves and stems of plants. A single large spring movements of beet leaf- overwintered female has been known hoppers have coincided with the sus- to deposit 675 eggs. The average is be- ceptible seedling stage of the plant. tween 300 and 400. The eggs hatch in Although the losses have been local in 5 to 40 days, depending on the tem- extent, they have dealt hard blows to perature. The young leafhoppers, the growers in affected areas. There is also nymphs, emerge from the eggs and The Beet Leafhopper 547 immediately begin to feed by insert- breeding grounds are more heavily in- ing their beaks into the plant tissue and fested than those farther away and are, sucking the juices. The tiny nymphs therefore, more seriously affected with are white, but in a few hours they curly top. Of the cultivated plants, darken considerably. As they grow th^y beets are the only important breeding shed their skins five times, becoming host. Spinach and Swiss chard are less larger after each molt. The older favorable. During the spring migration, nymphs are usually spotted with red the leafhopper will feed on beans, can- and brown. After the fifth miolt, they taloups, squash, tomatoes, and other become adults and have wings. crops but will not reproduce on them. The time required for nymphal de- It is during such feeding that the plants velopment from the time the insect are infected with the virus of curly top. hatches until it is adult is 3 to 6 weeks. The wild host plants of the beet leaf- Development from egg to adult takes hopper usually occur in large patches I to 2 months. The generations over- scattered over definite areas. Such lap considerably. All stages may be areas, where large numbers of favor- found in the same breeding area at the able host plants combine with favor- same time in summer. The beet leaf- able climatic conditions, are very pro- hopper breeds continuously during the ductive of leafhoppers. It is difficult to warm months, and nymphs may be trace the flights of such tiny insects, found at any time during the growing and much remains unknown about season. In the Central Columbia River their movements. Yet it is known in a area of Oregon and Washington, on general way that leafhoppers from any the Snake River Plains of southern one breeding ground infest the same Idaho, and in northern Utah, three cultivated areas year after year. generations arc produced each season. All the breeding grounds, except the In the warmer regions in Arizona and ones along the Rio Grande in New California, five or more generations Mexico and Texas, are v/est of the may develop. Continental Divide. All are in areas The first, or spring, generation is with a mean annual rainfall of not produced on spring weed hosts, chiefly more than 12 inches. In all except the mustards, that are rather short-lived Arizona and Rio Grande areas, the and mature and dry about the time the summers are dry, and the heaviest rain- spring-generation leafhopper reaches fall is in winter or spring. In southern the adult, or winged, stage. When Arizona and New Mexico and in south- weather conditions are favorable for western Texas, there is an appreciable flight, the leafhoppers move to their winter rainfall, with another rainy summer hosts, the progress of which period late in the summer. The quan- coincides with the maturation of the tity and distribution of rainfall in all insect. They travel with the wand and breeding grounds are such that prac- infest practically all host plants in their tically all agriculture depends upon path. Most of the favorable summer irrigation. The summers are hot and host plants are weeds. dry in all breeding areas, but the winter The infestation of crop plants is climate varies greatly. In the central incidental to the general movements of Columbia River breeding areas of Ore- the leafhopper, as they do not actively gon and Washington and on the lower seek these out but infest any favorable Snake River Plains of Idaho and host in their path. The leafhoppers eastern Oregon and in western Colo- moving into the cultivated areas alight rado, northern Nevada, and northern first in the fields nearest the spring Utah, heavy snows and subzero tem- breeding grounds and gradually move peratures are not uncommon. In the farther into the cultivated lands. Con- southern breeding areas, the moisture sequently beets, beans, tomatoes, and falls as rain, and the winters are short other susceptible crops nearest the and cool. 548 Yearbook of Agriculture 1952 The six most important breeding seasons they may be blown down the areas of the beet leafhopper are : Area Columbia Gorge into the Willamette I, San Joaquin Valley in California; Valley. area 2, lower Colorado River drainage Because the leafhopper does not hi- area; area 3, the Rio Grande area of bernate during the winter but must southern New Mexico and western feed when temperature permits activ- Texas ; area 4, scattered breeding areas ity, it requires a sequence of host of western Colorado, Nevada, and plants. The principal plants on which Utah; area 5, the lower Snake River it overwinters and produces one or Plains of Idaho and eastern Oregon; more spring generations in the major and area 6, the central Columbia River breeding areas are mustards. The prin- of Oregon and Washington. cipal spring host plants in the various The important breeding areas that breeding areas are: Area i, pepper- affect agriculture in the Great Valley grass {Lepidium nitidum and L. lati- of California lie along the foothills on pcs), desert plantains [Plantago insu- the west side of the San Joaquin Val- larisy P. fastigiatüy and P. erecta), and ley. The largest overwintering and filaree {Erodium cicutarium) ; area 2, spring breeding grounds are in the peppergrass {Lepidium lasiocarpum), eastern foothills of the Coastal Range, patata {Monolepis nuttalliana), and while the summer breeding grounds desert plantain {Plantago fastigiata) ; are in the Valley. area 3, perennial peppergrass {Lepi- The lower Colorado River drain- dium alyssoides) ; area 4, filaree, blis- .age breeding areas lie in south- tercress {Erysimum repandum) ^ and western Arizona, southeastern Cali- African mustard {Malcolmia afri- fornia, southern Nevada, and southern cana) ; area 5, flixweed {Descurainia Utah. These are the most extensive Sophia), green tansymustard {D. pin- spring breeding areas in the United nata ssp. ftlipes), perfoliate pepper- States, and leafhoppers moving from grass {Lepidium perfoliatum), and them affect agriculture in Arizona, tumblemustard {Sisymbrium altis si- Utah, and western Colorado. mum) ; area 6, filaree, tumblemustard, The breeding areas of western Colo- flixweed, and green tansymustard. rado, northern Nevada, and northern Russian-thistle {Salsola kali var. Utah are small, localized, and scat- tenuifolia) is the most important sum- tered, and leaiFhoppers from them mer weed host of the leafhopper in the affect adjacent agricultural crops. The western United States. Other impor- most important is within the Great tant summer host plants in various Salt Lake Basin. breeding areas are: Area i, bractscale In Idaho and eastern Oregon, the {Atriplex hracteosa) and fogweed {A, breeding grounds are on the Snake ex pansa) ; areas 2 and 3, chinch weed River Plains at elevations below ap- [Pectis papposa), Tidestromia lan- proximately 4,500 feet. Some summer guinosa, and Trianthema portulacas- reproduction occurs above this eleva- trum; area 3, Acanthochiton wrightii; tion, but these areas are generally re- areas 4, 5, and 6, smotherweed {Bassia populated each spring. The spring hyssopifolia), In California, Idaho, movements generally progress eastward Montana, Nevada, Utah, and Wyo- across the Snake River Plains. ming, the recently introduced halo- The breeding areas of Oregon and geton {Halogeton glomeratus), which Washington lie in the dry sagebrush is poisonous to livestock, is also a sum- plains of the Columbia Basin from the mer host. Siberian mustard {Chrispora Grand Coulee to central Oregon. Leaf- tenella) and kochia {Kochia scoparia) hoppers from those places infest sugar have invaded the breeding areas of beets and other susceptible crops in the southwestern Idaho, which emphasizes Yakima and Walla Walla Valleys and the fact that the beet leafhopper and other smaller irrigated areas. In certain curly top problem arc not static and The Beet Leafhopper 549 that the host-plant complex for both thistle in the San Joaquin Valley of leafhopper and curly top is constantly California, Snake River Plains of changing. Idaho, the central Columbia River With the maturing and drying of the area of Oregon and Washington, and summer hosts in the fall, the leafhop- to a lesser degree in Arizona, Colorado, pers move to their winter hosts. If the New Mexico, Texas, and Utah. summer weed hosts dry before the win- After fields are abandoned or range ter hosts germinate, the leafhoppers is overgrazed, a succession of plants may be forced to feed on perennial takes over. First come annual weeds, plants and shrubs, the only available which have little forage value, followed green vegetation, until the winter an- by some annual grasses. Then, if no nuals germinate. These temporary food further disturbance occurs, this condi- plants differ in the various breeding tion is followed by native perennial areas, as follows: Area i, desert salt- grasses and shrubs. The order of these bush {Atriplex polycarpa), spiny salt- changes in southern Idaho is: First, bush {A. s pinífera and Lepidospartum Russian-thistle; second, mustards; and squamatum) ; area 2, creosotcbush third, downy chess, an introduced an- {Larrea tridentata) ^ bur-sage {Fran- nual grass that is not a host of the beet seria dumosa), mesquite {Pr oso pis leafhopper. Our observations indicate juliflora), and spurges [Euphorbia that range fires generally have their spp.) ; area 3, creosotcbush, saltbush, origin in areas where downy chess and snakeweed {Giitierrezia spp.) ; forms the plant cover or where it has area 4, sagebrush {Artemisia triden- entered deteriorated sagebrush areas to tata), rabbitbrush ( Chrysothamnus such an extent that it will carry fires. spp.), and snakeweed; areas 5 and 6, During the fire season, it is the greatest sagebrush and rabbitbrush. If the sum- range fire hazard in the Intermountain mer hosts dry before the winter hosts Region; it will burn like tinder. If it germinate, there may be a heavy mor- is burned under favorable conditions, tality of the insects. If the winter hosts it may reseed itself and again form the germinate before the summer hosts dry cover, but under unfavorable condi- or are killed by frost, the mortality is tions, such as wind erosion and tramp- greatly reduced and high leafhopper ling by livestock, mustards, principally populations enter the winter. tumblemustard, and Russian-thistle Of the 16 important spring and may appear. The shift from mustards summier weed hosts of the beet leaf- and Russian-thistle to downy chess and hopper listed for areas i, 2, and 3, only then back to these w^eeds may continue filaree and Russian-thistle are intro- in an endless cycle. On burned areas, duced species ; in areas 4, 5, and 6, only mustards are generally first and then green tansymustard is a native. The downy chess, but with further disturb- others are introduced plants that have ance either Russian-thistle appears or become established on abandoned, the ground may become bare. Mixed waste, and deteriorated range lands. stands of Russian-thistle and mustards Evidently the geographical distribu- are the most important combination of tion of the beet leafhopper was once weed hosts for leafhopper reproduc- confined to the warmer arid regions of tion, since the leafhoppers can over- the southwestern United States but has winter and reproduce their spring and spread northward as its introduced summer generations in the same area. weed hosts became established. It is of interest to note that the first curly top THROUGHOUT THEIR GEOGRAPHICAL outbreak in California occurred after range, many leafhoppers are destroyed Russian-thistle had become established each year by parasites and predators, in the State. Later investigations have which attack the leafhopper in all its shown that the outbreaks arc in- stages and arc evidently a factor in fluenced by the acreage of Russian- reducing the population in the breed- 550 Yearbook of Agriculture 1952 ing grounds. Large numbers of eggs has given limited protection against are destroyed by minute parasitic wasps curly top under moderate to high in- that develop within them. The nymphs festations of the leafhopper in Utah. In and adults of the beet leafhopper are other instances where reinfestations do attacked by three groups of internal not usually occur, such as in fields of parasites—the big-eyed flies (Dori- sugar-beet seed, a single application of laidae), the parasitic wasps (Dryi- DDT in the fall has effectively reduced nidac ), and the twisted-winged para- curly top. sites (Strepsiptera). The flies and Other control methods have been wasps deposit their eggs in or on the developed. First, the major host plants leafhopper, and the resulting larvae of this insect were determined and develop within or partly within its methods for their replacement by non- body. Upon reaching maturity, the lar- host perennial grasses were studied. vae work out of the leafhopper, causing The replacement of weed hosts by per- its death. The twisted-winged parasites ennial grasses may best be accom- develop differently, as the female re- plished by reseeding the abandoned mains within the body of the leafhop- and burned areas. If native perennial per during its entire life and gives birth grasses are still present, protection to living young. These tiny larvae crawl against excessive grazing will accom- away, attach themselves to the first plish the same purpose. Because the leafhopper they find, and bore into its perennial grasses remain green until body. They seldom become of any real late in the season, they do not consti- importance, because the chances of tute a fire hazard when compared wdth their finding leafhoppers in which to downy chess. develop are slight. The tendency of the The second method is the chemical beet leafhopper to move about from control of the beet leafhopper in weed- host to host during the season appar- host areas. ently reduces the effect of these parasites. J. R. DOUGLASS, a South Carolinian, Several species of predacious bugs, obtained his entomological training in one being a big-eyed bug {Geocoris Clemson Agricultural College, Kansas pallens), destroy large numbers of leaf- State Agricultural College, Cornell hoppers by sucking out their body University, and Ohio State University, juices. Spiders, lizards, and birds re- He has been with the Department of duce the number of the insects. The Agriculture since igsi. From 1923 to grazing of livestock, principally sheep, igS4 he was in charge of the Estancia, destroys many eggs in the plants which N. Mex., laboratory, investigating in- they eat. sects affecting beans in the Southwest, Reducing curly top infection in sus- and since iQS^ he has been in charge ceptible crops by controlling the leaf- of the Twin Falls, Idaho, laboratory, hopper with insecticides is a difficult WILLIAM C. COOK is a graduate of problem, because continuous infection Cornell University and has a doctor's of the crops occurs by re infestation degree from the University of Minne- during the susceptible period. sota. He has been an entomologist in Applications of DDT wall reduce the Bureau of Entomology and Plant beet leafhopper numbers and have a Quarantine since 1930. Before that good residual toxicity, but it will not time he was employed by the Montana prevent the feeding of all leafhoppers Agricultural Experiment Station for that reinfcst the fields. In instances work on cutworms, especially the pale where reinfestation occurs over a 2- to western cutworm. He served from 1930 3-week period, applications of DDT to 1943 in California, studying the beet and other insecticides to tomato plants leafhopper. Since 1943 he has been have not reduced the incidence of curly stationed at Walla Walla, Wash., top. Double-hill planting of tomatoes siudying wireworms and the pea aphid»