http://hdl.handle.net/1813/43308

DISEASES OF LEAFY VEGETABLES AND CELERY Virus Diseases

Fact Sheet Page: 737.00 COOPERATIVE EXTENSION • NEW YORK STATE • CORNELL UNIVERSITY Date: 1 0-1984

mineral soils. Because these crops are aster yellows mycoplasma (A Y) depends Virus Diseases of often planted near one another, the vi­ upon the prevalence of the leafhopper Leafy Vegetables ruses or other agents infecting the crops vector. are the same, and they are transmitted and Celery by the same insect vectors. Lettuce and Endive Diseases The viruses infecting lettuce or endive by T. A. Zitter include lettuce mosaic virus (LMV), Lettuce mosaic virus (LMV) can Dept. of Plant Pathology cucumber mosaic virus (CMV), turnip infect all lettuce types (crisphead, cos, Cornell University mosaic virus (TuMV), broadbean wilt Boston, bibb, and leaf) as well as esca­ virus (BBWV), Bidens mottle virus role and endive. LMV is seedborne in and R. Provvidenti (BiMV), and beet western yellows virus all lettuce types, but not in endive; and Dept. of Plant Pathology (BWYV). Additional organisms infecting infected seed probably serves as the New York State Agricultural lettuce are lettuce big vein agent chief source of inoculum, although weed Experiment Station, Geneva (LBV A) and aster yellows mycoplasma hosts are also recognized. (AY). Plants infected through seed are Lettuce, endive (escarole), spinach, The viruses infecting spinach in New referred to as seedborne "mother" plants and celery are members of different York include LMV, CMV, BBWV, and because they can serve as virus reser­ plant families, but share many of the TuMV. voirs from which aphids can spread the same viral problems. In New York most The two most important virus dis­ virus to surrounding healthy plants. The of these crops are produced on organic eases of celery are CMV and celery mother plants show early mosaic symp­ soils, but they may also be grown on mosaic virus (CeMV); the occurence of toms, are stunted, and never develop marketable heads. Secondary infected planted crops. Although not extensively ida. Although not formally recognized plants show mosaic, leaf puckering, and tested on lettuce, mineral oil sprays are in this state, weed hosts such as shep­ deep or accentuated serration of the leaf known to significantly reduce secondary herdspurse are present. BWYV causes a margins in most lettuce types (fig. I). virus spread in many nonpersistent, pronounced chlorosis of the outer leaves Endive heads may be stunted, but gen­ aphid-transmitted virus diseases such as of lettuce (fig. 5) and escarole. erally show only mild mosaic symptoms. CMV, provided the treatment is begun Although spread by many of the Two methods for controlling LMV before primary inoculum exceeds 8-10% same aphid species that are vectors for are currently in use. First, because of and heavy virus pressure is not present the other common lettuce viruses, the prevalence of seedborne virus, let­ in adjoining fields. Spraying border BWYV is transmitted in a persistent tuce seed is tested by three methods areas with mineral oils is also beneficial. manner, meaning that a longer time is (direct reading of lettuce seedlings, inoc­ The technique used is sophisticated; required to acquire and then transmit ulation of ground-up seed with a sensi­ consult extension personnel for complete the virus. Insecticidal sprays would pre­ tive indexing host, or, more recently, a details. sumably help to delay the spread of this serological technique) to ensure that Because of the existence of several particular virus disease. each lettuce seed lot contains no infected strains of CMV in New York, breeding Lettuce big vein agent (LBV A) is seeds in a sample of 30,000 seeds (MTO of resistant lettuce varieties has been probably caused by a virus, although or mosaic tolerance zero). A more suc­ slowed, but is continuing. the virus particle has not been seen with cessful control measure is the incorpora­ Turnip mosaic virus (TuMV) is not a the electron microscope. This disease tion of virus resistance into the principal common disease of lettuce varieties, but differs greatly from the other lettuce lettuce types grown on both mineral and escarole and endive are very susceptible. virus diseases; its vector in nature is a organic soils. Susceptibility to TuMV was inadvert­ soilborne fungus (Olpidium brassicae). Cucumber mosaic virus (CMV) is the ently transferred to some lettuce varie­ The virus is acquired by the fungus pro­ most important virus disease of lettuce ties by breeding for resistance to downy toplast in virus-infected roots and is car­ in New York and the most difficult to mildew. TuMV typically causes veinal ried by fungal zoospores, which infect control. Because the virus can infect chlorosis and necrosis of lower leaves of healthy roots and release the virus. more than 775 plant species, including both lettuce (fig. 3) and endive, severely Infected lettuce plants are striking, many weed species (chickweed, milk­ stunting the plants and making the with leaves showing enlarged and light­ weed, purslane, dayflower, etc.), many heads unmarketable. ened veins and petioles (fig. 6). Leaves reservoirs exist to overwinter the virus Cruciferous weed hosts (shepherds­ are also thickened and distorted, and near growers' fields. Winged aphids purse, etc.) are the principal source of heads are smaller than normal. transmit the virus from bordering weedy inoculum for this aphid-transmitted Because of the soilborne nature of the areas to the crop to create primary virus, and controls discussed under disease, no practical control measures infection sites. Secondary infections CMV are applicable. are available. account for most virus spread and occur Broadbean wilt virus (BBWV), like Aster yellows mycoplasma (AY), when migrant aphids spread the virus CMV, can cause a serious disease of let­ formerly thought to be caused by a from infected primary lettuce plants to tuce in susceptible varieties, resulting in virus, can infect a wide range of plants surrounding healthy plants. When large large patches of infected plants (fig. 4). in addition to lettuce and celery. The migrant-aphid flights occur, an entire Symptoms are similar to those of LMV disease results in strikingly yellowed and field may become almost totally infected and CMV, but with low field tempera­ stunted plants (fig. 7), which are in a matter of weeks. tures the infected plants develop severe unmarketable. This disease may occur Although the symptoms of CMV veinal necrosis. Some varieties are very annually, its extent being determined by bear some resemblance to those of susceptible whereas others display good the preponderance of the aster leaf­ LMV, the mosaic is more intense with tolerance to infection. hopper vector (Macrosteles fascifrons). veinal chlorosis and, frequently, veinal BBWV is transmitted by aphids in a Controls are based upon the use of browning and necrosis when tempera­ nonpersistent manner. The major weed insecticidal sprays to reduce the only tures in the mid-50s or lower occur hosts in New York have been identified known vector. (fig. 2). as broadleaf plantain (Plantago major) Because weed hosts harboring CMV and buckhorn plantain (P. lanceolata). Virus Diseases of Spinach are common, a concerted effort must be Bidens mottle virus (BiMV) has been made by adjoining lettuce growers to recovered from lettuce and endive in Cucumber mosaic virus (CMV) infec­ make weed sanitation and other pro­ Orange County, but is not widely dis­ tion of spinach has long been called grams effective. Weed control must be tributed in the state. Symptoms caused "spinach blight" by growers, but should done before or soon after the crop is by BiMV are similar to those of LMV not be confused with fungal diseases for planted. Because migrant aphids in both lettuce and endive. The lettuce which the term blight is more com­ account for much of the virus spread variety Valmaine (a romaine or cos monly used. The disease is caused by and, normally, do not colonize lettuce, type) is naturally resistant to BiMV and CMV, which is covered in detail in insecticidal sprays are only minimally has been used in breeding programs for other sections of this fact sheet. Infected effective in reducing spread. Reducing joint resistance to BiMV and LMV. spinach plants may show a variety of primary inoculum in the crop is so criti­ BiMV is not seedborne in either let­ symptoms including stunting, yellowing, cal in delaying virus epidemics that tuce or endive, and principal weed hosts and mottling of the older leaves and major emphasis should be applied at for this aphid-transmitted virus are beg­ malformation of the younger leaves. this point. Make earliest plantings garticks, pepperweed, and others. Good resistance to CMV is available, downwind from weedy border areas, so Beet western yellows virus (BWYV) is but this resistance is temperature that older lettuce plantings do not serve an important virus disease of lettuce and dependent; at temperatures above 80° F as reservoirs of virus for subsequently endive in California, Arizona, and Flor- crown necrosis will develop (fig. 8), which is similar to infection with broad to infecting lettuce, can also infect spin­ fected when young will also be stunted. bean wilt virus (BBWV) without the ach. Neither LMV nor TuMV is seed­ The petioles on similarly infected plants need for high temperatures (fig. 9). borne in spinach, but an adjoining may also show slightly sunken, buff­ With the exception of the high tempera­ lettuce crop could inadvertently lead to colored lesions (fig. 11 ). If plants are ture response for CMV infection, resist­ infection of spinach. LMV symptoms on infected at an early age, inner petioles ance for CMV in spinach has provided spinach consist of bright yellow circular are also affected, making the plant an effective control measure for over 60 spots that coalesce into a diffuse dull unmarketable. years. chlorotic mottle. Young infected leaves Celery mosaic virus (CeMV), also Broadbean wilt virus (BBWV) has are small, mottled, and distorted. Older called western celery mosaic because it previously been mentioned in this plants are stunted, and old infected was first identified in California, can report. This virus does cause a major leaves die prematurely. TuMV -infected also be a serious disease of celery. The disease of spinach, particularly in the plants show diffuse mottle, leaf distor­ virus is transmitted by several aphid autumn crop when aphid vectors are tion, and stunting. Lower leaves become species in a nonpersistent manner and is most plentiful and much inoculum is necrotic and abscise prematurely. limited only to umbelliferous plants ( cel­ present from earlier plantings. ery, carrot, parsley, etc.). Plants infected Symptoms of BBWV closely resemble Celery Diseases at an early age are greatly stunted, and those caused by CMV, and therefore, the foliage, after showing early mosaic, identification is impossible under field Cucumber mosaic virus (CMV), also becomes cupped and malformed (fig. conditions (fig. 9). called southern celery mosaic, is the 12). Because of the limited host range, Control involves the removal of the principal virus disease of celery in New destruction of umbelliferous weeds is the principal weed hosts P. mqjor and York. The chief characteristics of this recommended control measure. P. lanceolata. Mineral oil sprays to virus disease and control measures have Aster yeUows mycoplasma (AY) may delay virus spread have been used only already been discussed. also infect celery on an annual basis. on a trial basis and have not been tested CMV symptoms consist of general This disease is described under "Lettuce under heavy disease pressure. mosaic, which, on older leaves infected and Endive Diseases." Lettuce mosaic and turnip mosaic earlier, develops into chlorotic yellowing viruses (LMV and TuMV), in addition and veinal necrosis (fig. 10). Plants in-

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Cooperative Extension, New York State College of Agriculture and Life Sciences, New York State College of Human Ecology, and New York State College of Veterinary Medicine at Cornell University, and U.S. Department of Agriculture, cooperating. In furtherance of acts of Congress May 8 and June 30, 1914, and providing equal opportunities in employment and programs. Lucinda A. Noble, Director. 11 /84 CRP 4M 9134e