| 1440043 |
Pythium diseases |
Pythium spp. |
Stem rot occurs on tobacco transplants shortly after they are set in the field. Stem rot may begin in the plant bed and be moved to the field on infected transplants, or it may begin after plants are set in the field. The development of stem rot is sporadic, being favored by wet weather and injured plants. Under favorable conditions, Pythium attacks the stems of newly set plants causing brown, watery lesions to develop near the soil line. As the fungus disease develops, stem tissue collapse and disintegrate, causing death of the plant. Stem rot usually appears as a watery soft rot; a cottony fungus mass may be present. Stem rot may be confused with sore shin or black shank, thus requiring microscopic examination for confirmation. |
| 1440089 |
phosphorous deficiency |
|
Tobacco deficient in P will be slow-growing, stunted, late maturing, and display a dark to very dark green color throughout the plant. Leaves tend to be more erect, closer together, shorter, and narrower than those receiving ample P. Temporary symptoms that have been reported as indicating P deficiencies include plants wilting during mid-day and occurrence on lower leaves of brown (dead) spots that are sometimes surrounded by a pale yellowish-green color. P deficiency symptoms are perhaps less evident and more difficult to recognize in the field than symptoms produced by deficiencies of any other essential plant nutrients. Therefore, soil and/or plant analyses are often necessary to verify suspected P deficiencies. |
| 1440047 |
black root rot |
Thielaviopsis basicola |
Uneven growth of tobacco in the field is indicative of black root rot. Affected plants often become yellowed and are smaller than neighboring healthy plants. Stunting is more evident during the early part of the growing season and during cool, wet seasons. On hot days, leaves of the diseased plants wilt more rapidly than those of healthy plants, but recover during the night. Plants usually grow out of the problem as soil temperatures rise, unless the variety is highly susceptible to the fungus and cool, wet soil conditions prevail. the most distinctive symptoms of black root rot occur on the roots. The entire root system is greatly reduced with smaller roots exhibiting a typical brown to black discoloration of their tips, and larger roots having brown or black spots on their surface. The outer root tissue may slough easily. |
| 1402019 |
blue mold |
Peronospora tabacina |
Blue mold can occur in the plant bed or field. Circular yellow spots up to one inch in diameter develop on the leaves. Blue-gray fungal growth is produced on the underside of these spots when the fungus is active. Spots become light brown when the leaf tissue dies. The disease first develops on lower leaves, but it rapidly spreads to upper leaves during wet, cool weather. |
| 1402056 |
bacterial barn rot |
|
During curing or storage, leaves may be rotted or discolored by these bacteria. The symptoms first appear as blackening of the veins or midribs. Large areas or whole leaves may decay. This soft rot bacterium is present in the soil and on green leaves. Barn rot begins when leaves are harvested wet and not properly dried before curing. This bacterium also causes hollow stalk in the field under wet conditions. |
| 1440003 |
canvas burn |
|
Canvas Burn indicated by yellowing or damage on leaf margins or tips is sometimes considered as cold injury since it usually occurs as the bed cover rubs leaves when temperatures are near freezing. |
| 1440002 |
cold injury (low temperature) |
|
Plant stunting and cupping or strapping of expanding leaves may result from cold injury. The strapped leaves and the bud area usually turn whitish or sometimes yellowish in color and show a restricted portion in leaf width as growth progresses. Plants will suffer less cold injury if covers are applied on the ground with no openings left at the edges. Rips in covers should be mended promptly. No other treatment is suggested since affected plants will resume normal growth after four or five consecutive days of warm weather. |
| 1402040 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank infection may occur on lower leaves of a plant due to spores being splashed onto them by hard rains. Large lesions (up to 3 inches) with a greenish-brown to yellow color are formed on the infected leaves. |
| 1440015 |
blue mold |
Peronospora tabacina |
Blue mold may occur on the plant anytime from seedling to harvest; however, young tissue is more susceptible than old tissue. The first evidence of blue mold in the field usually occurs on the leaves as yellow circular spots about the size of a nickel. The spots soon develop the characteristic bluish, downy fungal growth on the undersides of the leaves which is best seen in the morning when the leaf is wet. If spots develop on leaves that are expanding, a puckering of the leaf occurs. As spots age, they turn from yellow to tan or brown and often tear or drop out. If infection has occurred near or on a leaf vein, a localized systematic infection may occur. The affected vein becomes reddish-brown, and the area around the vein is yellowed and distorted. In newly set transplants, it is possible for the fungus to develop systematically, killing the main bud and resulting in stunting or death of the plant. Splitting the stalk of systematically infected plants reveals a reddish- brown discoloration in the vascular tissue beneath the epidermis. A one-sided systemically infection also occur, resulting in a deformed stalk and lodging of affected plants. During weather favorable for blue mold (cool, cloudy, and wet), the disease can develop rapidly, causing numerous leaf lesions which can result in leaf blighting and severe leaf loss. The disease may develop during hot, humid periods if cool nights exist. |
| 1402003 |
blue mold |
Peronospora tabacina |
Blue mold is shown above in a plant bed, but it can also occur in the field. |
| 1402057 |
bacterial barn rot |
|
During curing or storage, leaves may be rotted or discolored by these bacteria. The symptoms first appear as blackening of the veins or midribs. Large areas or whole leaves may decay. This soft rot bacterium is present in the soil and on green leaves. Barn rot begins when leaves are harvested wet and not properly dried before curing. This bacterium also causes hollow stalk in the field under wet conditions. |
| 1402023 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
This bacterial disease can occur in the plant bed or field. It most commonly occurs in the field in mid-summer during periods of cloudy, wet weather. Leaf spots develop, which are 1/4 to 1/2 inch in diameter and dark brown to black in color. They are limited by leaf veins making spots angular in shape. Concentric rings may be evident within the spots. Spots may coalesce, forming large irregular dead areas. The center of the spots may fall out, giving the leaf a ragged appearance. Leaves will turn yellow when numerous spots are present. Angular leafspot is most severe on lower leaves. |
| 1440057 |
bacterial hollow stalk |
Erwinia aroideae |
Bacterial hollow stalk is first noticed when leaves begin to drop or turn yellow and hang down the stalk. A watery soft rot develops at the base of the affected leaves and often extends up the midrib. The disease may begin at any point of injury, but it often starts at injuries caused by topping or suckering. The pith in the center of the stalk is destroyed, leaving a hollow shell. As the disease moves down the stalk, the leaves droop. Later they drop off, leaving a bare stalk. Hollow stalk usually appears after topping or suckering and may continue to develop after the tobacco is hung in the barn, causing barn rot. Related bacteria may also cause a soft rot of lower leaves during rainy weather. |
| 1440050 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank is primarily a disease of the roots and the lower stalk of the tobacco. The symptoms of black shank vary with weather conditions, age of plants, stage of disease development, degree of plant resistance, and virulence of the soil-borne fungal pathogen. Stunting is often the first symptom of black shank, but the disease is seldom recognized until plants wilt. At first, wilted plants will recover in the evening hours, but later become permanently wilted, with leaves turning yellow and hanging down the stalk. During the early stages of disease development, an examination of the plant will show a black discoloration of one or more of the larger roots and the interior of the lower stalk. As the disease progresses, the lower part of the stalk becomes black near the soil line, hence the name black shank. In advanced stages of the disease, the tissues in the center of the lower stalk become blackened, and as the pith dries, it becomes segmented into discs. |
| 1440049 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank is primarily a disease of the roots and the lower stalk of the tobacco. The symptoms of black shank vary with weather conditions, age of plants, stage of disease development, degree of plant resistance, and virulence of the soil-borne fungal pathogen. Stunting is often the first symptom of black shank, but the disease is seldom recognized until plants wilt. At first, wilted plants will recover in the evening hours, but later become permanently wilted, with leaves turning yellow and hanging down the stalk. During the early stages of disease development, an examination of the plant will show a black discoloration of one or more of the larger roots and the interior of the lower stalk. As the disease progresses, the lower part of the stalk becomes black near the soil line, hence the name black shank. In advanced stages of the disease, the tissues in the center of the lower stalk become blackened, and as the pith dries, it becomes segmented into discs. |
| 1440033 |
Tobacco Etch Virus |
Potyvirus TEV |
The first symptom of TEV infection is a pronounced vein clearing on expanding leaves. This is followed by necrosis of a thin line of tissue along the veins, resulting in an etched pattern. Subsequently, young leaves develop a mosaic which fades to mottling as the leaf ages. Etching and more pronounced veinal necrosis is common. Plant growth is retarded, resulting in stunting, especially when young plants are infected. The virus overwinters in perennial solanaceous weeds and is transmitted to tobacco by migrating aphids. TEV often occurs in combination with other aphid-borne viruses. Tobacco etch is one of the most common virus diseases of burley. |
| 1440051 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank is primarily a disease of the roots and the lower stalk of the tobacco. The symptoms of black shank vary with weather conditions, age of plants, stage of disease development, degree of plant resistance, and virulence of the soil-borne fungal pathogen. Stunting is often the first symptom of black shank, but the disease is seldom recognized until plants wilt. At first, wilted plants will recover in the evening hours, but later become permanently wilted, with leaves turning yellow and hanging down the stalk. During the early stages of disease development, an examination of the plant will show a black discoloration of one or more of the larger roots and the interior of the lower stalk. As the disease progresses, the lower part of the stalk becomes black near the soil line, hence the name black shank. In advanced stages of the disease, the tissues in the center of the lower stalk become blackened, and as the pith dries, it becomes segmented into discs. |
| 1440016 |
blue mold |
Peronospora tabacina |
Blue mold may occur on the plant anytime from seedling to harvest; however, young tissue is more susceptible than old tissue. The first evidence of blue mold in the field usually occurs on the leaves as yellow circular spots about the size of a nickel. The spots soon develop the characteristic bluish, downy fungal growth on the undersides of the leaves which is best seen in the morning when the leaf is wet. If spots develop on leaves that are expanding, a puckering of the leaf occurs. As spots age, they turn from yellow to tan or brown and often tear or drop out. If infection has occurred near or on a leaf vein, a localized systematic infection may occur. The affected vein becomes reddish-brown, and the area around the vein is yellowed and distorted. In newly set transplants, it is possible for the fungus to develop systematically, killing the main bud and resulting in stunting or death of the plant. Splitting the stalk of systematically infected plants reveals a reddish- brown discoloration in the vascular tissue beneath the epidermis. A one-sided systemically infection also occur, resulting in a deformed stalk and lodging of affected plants. During weather favorable for blue mold (cool, cloudy, and wet), the disease can develop rapidly, causing numerous leaf lesions which can result in leaf blighting and severe leaf loss. The disease may develop during hot, humid periods if cool nights exist. |
| 1440058 |
bacterial hollow stalk |
Erwinia aroideae |
Bacterial hollow stalk is first noticed when leaves begin to drop or turn yellow and hang down the stalk. A watery soft rot develops at the base of the affected leaves and often extends up the midrib. The disease may begin at any point of injury, but it often starts at injuries caused by topping or suckering. The pith in the center of the stalk is destroyed, leaving a hollow shell. As the disease moves down the stalk, the leaves droop. Later they drop off, leaving a bare stalk. Hollow stalk usually appears after topping or suckering and may continue to develop after the tobacco is hung in the barn, causing barn rot. Related bacteria may also cause a soft rot of lower leaves during rainy weather. |
| 1440054 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank is primarily a disease of the roots and the lower stalk of the tobacco. The symptoms of black shank vary with weather conditions, age of plants, stage of disease development, degree of plant resistance, and virulence of the soil-borne fungal pathogen. Stunting is often the first symptom of black shank, but the disease is seldom recognized until plants wilt. At first, wilted plants will recover in the evening hours, but later become permanently wilted, with leaves turning yellow and hanging down the stalk. During the early stages of disease development, an examination of the plant will show a black discoloration of one or more of the larger roots and the interior of the lower stalk. As the disease progresses, the lower part of the stalk becomes black near the soil line, hence the name black shank. In advanced stages of the disease, the tissues in the center of the lower stalk become blackened, and as the pith dries, it becomes segmented into discs. |
| 1440031 |
Tobacco Ringspot Virus |
Nepovirus TRSV |
Tobacco ringspot has the most distinctive symptoms of the virus diseases. The name truly describes the disease because chlorotic or necrotic rings occur in the leaf. A concentric line pattern of chlorotic and necrotic tissue, often forming an "oak leaf" pattern, is very common. The symptoms occasionally are confirmed to one side of the plant. The disease appears early in the season, usually with initial growth after transplanting. Most infected plants recover as new symptomless leaves develop. The virus is transmitted by nematodes. In the field, infected plants may appear alone or clustered. Ringspot may occur in the plant bed. |
| 1440023 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
Wildfire is caused by a strain of the same bacterium that causes angular leaf spot. The wildfire strain produces a toxin in which causes conspicuous chlorotic halos to develop around infection sites. Most burley varieties are resistant to wildfire. |
| 1440028 |
frog-eye leafspot |
Cercospora nicotianae |
Frogeye may develop on the leaves of tobacco in the plant bed, field, or barn. The spots on the leaves are quite distinct, typically circular, with a reddish-brown margin and tan or grey colored papery centers in which black masses (fruiting bodies) of the fungus may be found. Frogeye usually occurs on the lower leaves but moves up the plant as the season progresses, especially as the nitrogen supply is depleted. Sudden development of large dead in the upper leaves may occur near harvest. Frogeye may be confused with brown spot, wildfire, angular leaf spot, weather fleck, and physiological spotting, and it requires microscopic examination for diagnosis. Green spots on the leaves of cured tobacco may be the result of frogeye infection near harvest. |
| 1440021 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
Symptoms of angular leaf spot in the field are similar to those produced in the plant bed. Spots are circular to slightly angular. After wet, rainy weather, spots may be numerous. The spots are tan at first but turn black with age. Centers of spots may drop out producing a shot-hole or ragged appearance. This bacterial disease is generally worse on the windward side of plants where watersoaking from driving rains or sandblasting tends to enhance infection. |
| 1440024 |
brown spot |
Alternaria alternata |
Symptoms of the brown spot fungus first appear on the lower leaves. Spots are brown with sharply defined margins and may be surrounded by yellow halos. The primary distinguishing characteristics of brown spot are the dark concentric rings within spots that give it a target-like appearance. With magnification, reproductive structures of the casual agent are seen as tufts of black fungal spores (conidia). Under severe conditions, spots are numerous, may coalesce, and give the leaf a ragged appearance as the infected tissue falls out. |
| 1440020 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
Symptoms of angular leaf spot in the field are similar to those produced in the plant bed. Spots are circular to slightly angular. After wet, rainy weather, spots may be numerous. The spots are tan at first but turn black with age. Centers of spots may drop out producing a shot-hole or ragged appearance. This bacterial disease is generally worse on the windward side of plants where watersoaking from driving rains or sandblasting tends to enhance infection. |
| 1440029 |
Tobacco Ringspot Virus |
Nepovirus TRSV |
Tobacco ringspot has the most distinctive symptoms of the virus diseases. The name truly describes the disease because chlorotic or necrotic rings occur in the leaf. A concentric line pattern of chlorotic and necrotic tissue, often forming an "oak leaf" pattern, is very common. The symptoms occasionally are confirmed to one side of the plant. The disease appears early in the season, usually with initial growth after transplanting. Most infected plants recover as new symptomless leaves develop. The virus is transmitted by nematodes. In the field, infected plants may appear alone or clustered. Ringspot may occur in the plant bed. |
| 1402029 |
Potato Virus Y |
Potyvirus PVY |
Mild symptoms of this virus disease include leaf mottling and crinkling, prominent veins, and curved midribs. Leaf tissue, except for that around the veins, turns slightly yellow in color. This gives the veins a green-banded appearance. As the leaves mature, sunken brown spots may develop on the upper surface of the midrib. Systematic necrosis frequently occurs in cultivars resistant to root-knot nematodes. As lower leaves begin to ripen, midribs may turn black; leaves may die and fall from the stalk. If the stalk is split, areas of black discoloration will be found extending from top to bottom of the plant. |
| 1402031 |
Tobacco Ringspot Virus |
Nepovirus TRSV |
The virus disease first appears as circular line patterns of yellow and brown tissue on young leaves. These line patterns may follow the leaf veins and form the outline of an oak leaf. Some of the plant tissue may die, resulting in a "shot-hole" appearance. Symptom severity varies from a few ringspots to a dwarfed plant with numerous patterns and ragged leaves. Ringspot usually appears on scattered plants and causes little or no economic loss. |
| 1402026 |
Tobacco Mosaic Virus |
Tobamovirus TMV |
The first symptom of this virus disease is a light green coloration between the veins of young leaves. This is followed quickly by the development of a "mosaic" or mottled pattern of light and dark green areas in the leaves. These symptoms develop quickly and are more pronounced on younger leaves. Mosaic does not result in plant death, but if infection occurs early in the season, plants are stunted. Lower leaves are subject to "mosaic burn," especially during periods of hot and dry weather. In these cases, large dead areas develop in the leaves. This constitutes one of the most destructive phases of tobacco mosaic virus infection. Infected leaves may be crinkled, puckered, or elongated. |
| 1402021 |
blue mold |
Peronospora tabacina |
Systemic infection begins in leaf veins which turn reddish. Systemically infected stalks are stunted. The leaves are mottled and distorted. When a leaf is removed, discolored vascular tissue is present where the leaf was attached. Often, this discoloration extends down the stalk. The terminal bud may die, and the central portion of the stalk in the terminal bud region will be darkened or deeply discolored. Excessive numbers of ground suckers may develop. |
| 1402022 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
This bacterial disease can occur in the plant bed or field. It most commonly occurs in the field in mid-summer during periods of cloudy, wet weather. Leaf spots develop, which are 1/4 to 1/2 inch in diameter and dark brown to black in color. They are limited by leaf veins making spots angular in shape. Concentric rings may be evident within the spots. Spots may coalesce, forming large irregular dead areas. The center of the spots may fall out, giving the leaf a ragged appearance. Leaves will turn yellow when numerous spots are present. Angular leafspot is most severe on lower leaves. |
| 1402025 |
brown spot |
Alternaria alternata |
This fungal disease appears first on the older leaves as circular, brown spots (1/4 to 1 1/4 inches in diameter) with sharply defined margins. Concentric circles (rings) are often noticeable within the spots. As the leaves approach maturity, a yellowish "halo" of varying width often forms around the lesion. Lesions may merge, forming large areas of dead tissue. During humid weather, sporulation of the fungus may be abundant, giving the lesions a black, dusty appearance. Brown spot is most severe as the plant approaches maturity, and the disease progresses from the lower to the upper leaves. Disease severity depends much on the weather, the overall health of the plant, varietal tolerance, and harvest rate. |
| 1402039 |
Phytophthora blight |
Phytophthora nicotianae |
Plants cut longitudinally reveal brown to black discoloration of the pith, which is often separated into discs. Discing may not occur in resistant varieties and only a small portion of the pith may be discolored. |
| 1402020 |
blue mold |
Peronospora tabacina |
Systemic infection begins in leaf veins which turn reddish. Systemically infected stalks are stunted. The leaves are mottled and distorted. When a leaf is removed, discolored vascular tissue is present where the leaf was attached. Often, this discoloration extends down the stalk. The terminal bud may die, and the central portion of the stalk in the terminal bud region will be darkened or deeply discolored. Excessive numbers of ground suckers may develop. |
| 1440022 |
wildfire of tobacco |
Pseudomonas syringae pv. tabaci |
Wildfire is caused by a strain of the same bacterium that causes angular leaf spot. The wildfire strain produces a toxin in which causes conspicuous chlorotic halos to develop around infection sites. Most burley varieties are resistant to wildfire. |
| 1440045 |
Rhizoctonia damping-off, blight and rot |
Rhizoctonia solani |
This fungus usually appears first in the plant bed, but infections occur at any growth stage. Sore shin appears as a brown discoloration of the transplant stem near or below the soil line. The affected area may increase in size after the plant is set in the field, sometimes extending several inches up the stalk. The stalk of an infected plant becomes brittle and may break up easily under pressure. Lower leaves of older plants may turn yellow; the plant is often stunted. Plants may wilt during the heat of the day. Diseased plants usually appear scattered in the field. In advanced stages of sore shin, large stalks may be dry and brown inside. Stalks with only slight infections produce near normal growth and yields unless the plants become stressed. Symptoms of sore shin may be confused with stem rot or black shank; accurate diagnosis requires microscopic examination. |
| 1402018 |
blue mold |
Peronospora tabacina |
Blue mold can occur in the plant bed or field. Circular yellow spots up to one inch in diameter develop on the leaves. Blue-gray fungal growth is produced on the underside of these spots when the fungus is active. Spots become light brown when the leaf tissue dies. The disease first develops on lower leaves, but it rapidly spreads to upper leaves during wet, cool weather. |
| 1440044 |
Rhizoctonia damping-off, blight and rot |
Rhizoctonia solani |
This fungus usually appears first in the plant bed, but infections occur at any growth stage. Sore shin appears as a brown discoloration of the transplant stem near or below the soil line. The affected area may increase in size after the plant is set in the field, sometimes extending several inches up the stalk. The stalk of an infected plant becomes brittle and may break up easily under pressure. Lower leaves of older plants may turn yellow; the plant is often stunted. Plants may wilt during the heat of the day. Diseased plants usually appear scattered in the field. In advanced stages of sore shin, large stalks may be dry and brown inside. Stalks with only slight infections produce near normal growth and yields unless the plants become stressed. Symptoms of sore shin may be confused with stem rot or black shank; accurate diagnosis requires microscopic examination. |
| 1402041 |
Southern bacterial wilt |
Ralstonia solanacearum (except Race 3 Biovar 2) |
The first symptom of this bacterial disease is the drooping of one or two leaves which may recover at night. Only half of a leaf may wilt initially. Leaves on one sides of the plant wilt first, while leaves on the other side appear normal. This unilateral wilting is very characteristic. Affected leaves become light green to yellow and occasionally appear scaled. Eventually most or all of the roots become blackened and decay. Infected roots become soft and slimy if adequate water is present. Tan or brown discoloration develops in the vascular tissue just beneath the bark. Pith and cortex also become discolored when involved. Longitudinal sections through affected stalks have narrow, brown lines in the xylem tissue nearest the pith. A slimy substance often oozes from a stalk cut in cross section. If a stalk segment containing discolored vascular tissue is placed in a clear container of water, milky strands stream from the edge of the tissue. |
| 1440039 |
Tobacco Streak Virus |
Ilarvirus TSV |
Streak in burley tobacco follows a typical pattern wherein vigorously growing plants suddenly develop a severe necrotic streaking of the bud leaves and stalk. The stalk is marked by a depressed dark area, and the midveins of the leaves have dead streaks in them. The leaves curl downward, are distorted, wilted, and usually chlorotic. When death of the affected plant seems imminent, growth resumes from the bud with resulting leaves appearing normal except for occasional faint mottling. Leaves damaged early are permanently dwarfed and exhibit numerous necrotic areas. The virus is common in sweet clover and is presumably moved to tobacco by an insect, probably by thrips. |
| 1440055 |
Fusarium wilt |
Fusarium oxysporum f.sp. nicotianae |
Fusarium wilt usually appears in clusters of plants in the field. Yellowing and drying of the leaves on one side of a tobacco plant are typical symptoms. If a strip of the outer stem tissue (bark) is removed from the side of the stalk with yellowed leaves, a brown discoloration of the wood or vascular tissue is present rather than the normal white color. This discoloration usually can be traced from the affected part of the stalk down into the roots. The midribs of leaves on the affected side of the plant are often curved to one side with half of the leaf yellowed and the other half remaining green. In a young plant, the bud may bend toward the side of the plant with the yellowed leaves. Wilting, although implied by the name of this fungal disease, is not typical of diseased plants. |
| 1440001 |
cold injury (low temperature) |
|
Plant stunting and cupping or strapping of expanding leaves may result from cold injury. The strapped leaves and the bud area usually turn whitish or sometimes yellowish in color and show a restricted portion in leaf width as growth progresses. Plants will suffer less cold injury if covers are applied on the ground with no openings left at the edges. Rips in covers should be mended promptly. No other treatment is suggested since affected plants will resume normal growth after four or five consecutive days of warm weather. |
| 1402055 |
bacterial soft rot |
Pectobacterium carotovorum ssp. carotovorum |
This bacterial soft rot usually first appears following topping and suckering. Although the bacteria can invade the stalk through any wound, they usually enter through the break at the top. The pith rapidly turns brown and collapses in a watery rot. A foul odor is evident as the stalks become hollow. Leaves adjacent to the rotting pith will wilt. The rot may extend into the leaves through the midrib. The midribs turn black and the leaves droop. If infected leaves are placed in the barn, soft rot may continue to develop as barn rot. |
| 1402008 |
anthracnose |
Colletotrichum nicotianae |
This fungal disease is encountered in tobacco seed beds and occasionally in the field. Small gray-white, usually circular, spots develop on leaves. As lesions age and dry, they become papery and thin and are surrounded by a raised water-soaked border. Leaf tissues, especially veins and midribs, may appear "pitted" or sunken when viewed from the underside. The lesions become brown. Larger spots may have a dark brown center. Lateral veins on the lower leaf surface may turn dark. Affected leaves may become wrinkled and/or distorted. As the disease continues, the entire leaf may die. Small plants may be killed, resulting in large barren spots in plant beds. In the field, leaf lesions may be followed by cankers on midribs and stems. Anthracnose is favored by wet conditions and is sometimes confused with weather fleck. Symptoms of anthracnose are also similar to those of target spot. Target spot has more consistently circular, pin-head sized lesions which usually do not affect the major leaf veins until the whole leaf begins to die, whereas anthracnose often attacks leaf veins and petioles early in the disease development. |
| 1402027 |
Tobacco Mosaic Virus |
Tobamovirus TMV |
The first symptom of this virus disease is a light green coloration between the veins of young leaves. This is followed quickly by the development of a "mosaic" or mottled pattern of light and dark green areas in the leaves. These symptoms develop quickly and are more pronounced on younger leaves. Mosaic does not result in plant death, but if infection occurs early in the season, plants are stunted. Lower leaves are subject to "mosaic burn," especially during periods of hot and dry weather. In these cases, large dead areas develop in the leaves. This constitutes one of the most destructive phases of tobacco mosaic virus infection. Infected leaves may be crinkled, puckered, or elongated. |
| 1440046 |
black root rot |
Thielaviopsis basicola |
Uneven growth of tobacco in the field is indicative of black root rot. Affected plants often become yellowed and are smaller than neighboring healthy plants. Stunting is more evident during the early part of the growing season and during cool, wet seasons. On hot days, leaves of the diseased plants wilt more rapidly than those of healthy plants, but recover during the night. Plants usually grow out of the problem as soil temperatures rise, unless the variety is highly susceptible to the fungus and cool, wet soil conditions prevail. the most distinctive symptoms of black root rot occur on the roots. The entire root system is greatly reduced with smaller roots exhibiting a typical brown to black discoloration of their tips, and larger roots having brown or black spots on their surface. The outer root tissue may slough easily. |
| 1440052 |
Phytophthora blight |
Phytophthora nicotianae |
Black shank is primarily a disease of the roots and the lower stalk of the tobacco. The symptoms of black shank vary with weather conditions, age of plants, stage of disease development, degree of plant resistance, and virulence of the soil-borne fungal pathogen. Stunting is often the first symptom of black shank, but the disease is seldom recognized until plants wilt. At first, wilted plants will recover in the evening hours, but later become permanently wilted, with leaves turning yellow and hanging down the stalk. During the early stages of disease development, an examination of the plant will show a black discoloration of one or more of the larger roots and the interior of the lower stalk. As the disease progresses, the lower part of the stalk becomes black near the soil line, hence the name black shank. In advanced stages of the disease, the tissues in the center of the lower stalk become blackened, and as the pith dries, it becomes segmented into discs. |
| 1402054 |
bacterial soft rot |
Pectobacterium carotovorum ssp. carotovorum |
This bacterial soft rot usually first appears following topping and suckering. Although the bacteria can invade the stalk through any wound, they usually enter through the break at the top. The pith rapidly turns brown and collapses in a watery rot. A foul odor is evident as the stalks become hollow. Leaves adjacent to the rotting pith will wilt. The rot may extend into the leaves through the midrib. The midribs turn black and the leaves droop. If infected leaves are placed in the barn, soft rot may continue to develop as barn rot. |
| 1440009 |
anthracnose |
Colletotrichum nicotianae |
Symptoms of anthracnose include spotting of the leaves, development of cankers on midribs and veins of leaves, and eventual stunting and/or death of transplants. Leaf spots are at first pinpoint size, water-soaked, and depressed. They enlarge to approximately 3 mm in diameter, are light tan in the center, and have raised dark borders. Veins and midribs are often infected, causing the leaf to become distorted. On plants ready to transplant, large red-brown cankers can develop on the stems and petioles. Severely affected plants are killed. With the aid of a hand lens, fruiting bodies called acervuli can be seen in affected areas. These fruiting bodies produce pink spore masses and may have black bristle-like appendages called setae. The disease is most common in plant beds that are weedy and/or deficient in nitrogen. |
| 1440027 |
Phoma blight |
Phoma exigua var. exigua |
Spots are tan colored, with minute dark circular specks present on the surface of the spot. Brown spot and ragged leaf spot may be confused. The presence of distinct, circular, black fruiting bodies (pycnidia), which may be seen under magnification, distinguishes this disease from brown spot. The tissue in the spot may become papery-thin, tearing easily and giving the spot a ragged appearance. This disease is usually of minor importance, showing up late in the season on the lower leaves. |
| 1402042 |
Southern bacterial wilt |
Ralstonia solanacearum (except Race 3 Biovar 2) |
The first symptom of this bacterial disease is the drooping of one or two leaves which may recover at night. Only half of a leaf may wilt initially. Leaves on one sides of the plant wilt first, while leaves on the other side appear normal. This unilateral wilting is very characteristic. Affected leaves become light green to yellow and occasionally appear scaled. Eventually most or all of the roots become blackened and decay. Infected roots become soft and slimy if adequate water is present. Tan or brown discoloration develops in the vascular tissue just beneath the bark. Pith and cortex also become discolored when involved. Longitudinal sections through affected stalks have narrow, brown lines in the xylem tissue nearest the pith. A slimy substance often oozes from a stalk cut in cross section. If a stalk segment containing discolored vascular tissue is placed in a clear container of water, milky strands stream from the edge of the tissue. |
| 1440040 |
Potato Virus Y |
Potyvirus PVY |
The initial symptom of PVY infection is vein clearing on newly developing leaves. The extent of the vein clearing is intermediate between that caused by TEV and TVMV. Leaves then develop a faint mottling and the characteristic vein banding: dark green bands along the veins with lighter green tissue adjacent. The pattern is more regular than that caused by TVMV. Veinlets and veins may become necrotic on plants infected with severe strains of PVY. This Virus is transmitted from vegetables and weeds to tobacco by migrating aphids. |
| 1440059 |
bacterial black stalk |
Erwinia spp. |
Bacterial Black Stalk is similar to hollow stalk and occasionally occurs in burley during periods of drought. The bark of the stalk is blackened from the ground upward, but the pith is not destroyed. The leaves are bright yellow with decayed midribs. |
| 1402053 |
charcoal root rot |
Macrophomina phaseoli |
Plants are usually predisposed to this fungus disease by certain practices such as the application of contact sucker control materials during hot weather. Irregular black lesions may extend from the soil surface to the top of the plant. A basal rotting of plants may occur, although roots are usually not affected . Stalks cut longitudinally exhibit appreciable pith and wood decay. In advanced stages, the pith may completely disappear resulting in a hollow stalk. Leaves of affected plants turn yellow, droop, and die. |
| 1440008 |
blue mold |
Peronospora tabacina |
Blue mold can be very devastating to tobacco plants in the bed. Usually, the first symptom of blue mold in the bed is yellowed areas of diseased plants. The leaves of affected plants in these yellowed areas will have a cupped appearance, and the undersides of the leaves will show tell-tale, blue-gray downy fungal growth. Older plants can be deformed and twisted, and the main growing point eventually is killed. Veins in affected areas of twisted leaves are reddish-brown and can become necrotic. On older plants, definite yellow spots with bluish fungal growth on the underside of leaves can occur. |
| 1440025 |
brown spot |
Alternaria alternata |
Symptoms of the brown spot fungus first appear on the lower leaves. Spots are brown with sharply defined margins and may be surrounded by yellow halos. The primary distinguishing characteristics of brown spot are the dark concentric rings within spots that give it a target-like appearance. With magnification, reproductive structures of the casual agent are seen as tufts of black fungal spores (conidia). Under severe conditions, spots are numerous, may coalesce, and give the leaf a ragged appearance as the infected tissue falls out. |
| 1402006 |
Pythium diseases |
Pythium spp. |
Under severe situations, the plant bed may be bare. Newly transplanted tobacco is vulnerable to damping-off during cool, wet weather. Pythium lesions are large and wet. They extend up the plant tissue or encompass the entire stem. |
| 1440038 |
Tobacco Streak Virus |
Ilarvirus TSV |
Streak in burley tobacco follows a typical pattern wherein vigorously growing plants suddenly develop a severe necrotic streaking of the bud leaves and stalk. The stalk is marked by a depressed dark area, and the midveins of the leaves have dead streaks in them. The leaves curl downward, are distorted, wilted, and usually chlorotic. When death of the affected plant seems imminent, growth resumes from the bud with resulting leaves appearing normal except for occasional faint mottling. Leaves damaged early are permanently dwarfed and exhibit numerous necrotic areas. The virus is common in sweet clover and is presumably moved to tobacco by an insect, probably by thrips. |
| 1440026 |
Phoma blight |
Phoma exigua var. exigua |
Spots are tan colored, with minute dark circular specks present on the surface of the spot. Brown spot and ragged leaf spot may be confused. The presence of distinct, circular, black fruiting bodies (pycnidia), which may be seen under magnification, distinguishes this disease from brown spot. The tissue in the spot may become papery-thin, tearing easily and giving the spot a ragged appearance. This disease is usually of minor importance, showing up late in the season on the lower leaves. |
| 1402046 |
southern blight |
Sclerotium rolfsii |
With this fungal disease, leaves of infected plants rapidly turn yellow, wilt, and die. The dried, brown leaves hang down the dying stalk. The root system remains healthy prior to the death of the plant. Infected plants are usually scattered singly through the field or occur in small groups. Symptoms may be confused with those of black shank. During warm, moist weather, the fungus produces a white cottony growth from the discolored stalk lesions. Discing of the pith similar to black shank may occur, but it is much lighter in color and not as well-organized. Infected stalks easily break at the stalk lesion. |
| 1402052 |
charcoal root rot |
Macrophomina phaseoli |
Plants are usually predisposed to this fungus disease by certain practices such as the application of contact sucker control materials during hot weather. Irregular black lesions may extend from the soil surface to the top of the plant. A basal rotting of plants may occur, although roots are usually not affected . Stalks cut longitudinally exhibit appreciable pith and wood decay. In advanced stages, the pith may completely disappear resulting in a hollow stalk. Leaves of affected plants turn yellow, droop, and die. |
| 1402049 |
Rhizoctonia damping-off, blight and rot |
Rhizoctonia solani |
This soil-borne fungus infects the lower stem of the tobacco plant. Symptoms begin on seedlings and transplants as a dark brown lesion on the stem near or below ground level. Lesions vary in size and number depending on environmental conditions. In wet, cool weather, the lesions may enlarge upward and around the stem until the plant falls over. This may be confused with black shank or Pythium damping-off. On older plants, a dark brown lesion up to several inches long occurs at or near the soil line. It may girdle the stalk which becomes hard and brittle. The stalk may break at this lesion. The plant may be stunted with yellow to brown and/or wilted leaves. Roots usually show no evidence of decay. |
| 1402050 |
Rhizoctonia damping-off, blight and rot |
Rhizoctonia solani |
This soil-borne fungus infects the lower stem of the tobacco plant. Symptoms begin on seedlings and transplants as a dark brown lesion on the stem near or below ground level. Lesions vary in size and number depending on environmental conditions. In wet, cool weather, the lesions may enlarge upward and around the stem until the plant falls over. This may be confused with black shank or Pythium damping-off. On older plants, a dark brown lesion up to several inches long occurs at or near the soil line. It may girdle the stalk which becomes hard and brittle. The stalk may break at this lesion. The plant may be stunted with yellow to brown and/or wilted leaves. Roots usually show no evidence of decay. |
| 1440037 |
Cucumber Mosaic Virus |
Cucumovirus CMV |
The symptoms of CMV infection are quite striking and resemble those caused by other aphid-borne viruses and tobacco mosaic virus. Typical symptoms are mottling or mosaic of the young leaves, sometimes accompanied by stunted, narrow, or distorted older leaves. Scalding of infected leaves may also occur. Cucumber mosaic virus is transmitted by aphids migrating from infected weeds and vegetable crops. CMV is relatively rare in burley. |
| 1440034 |
Tobacco Etch Virus |
Potyvirus TEV |
The first symptom of TEV infection is a pronounced vein clearing on expanding leaves. This is followed by necrosis of a thin line of tissue along the veins, resulting in an etched pattern. Subsequently, young leaves develop a mosaic which fades to mottling as the leaf ages. Etching and more pronounced veinal necrosis is common. Plant growth is retarded, resulting in stunting, especially when young plants are infected. The virus overwinters in perennial solanaceous weeds and is transmitted to tobacco by migrating aphids. TEV often occurs in combination with other aphid-borne viruses. Tobacco etch is one of the most common virus diseases of burley. |
| 1402048 |
southern blight |
Sclerotium rolfsii |
The base of the stalk shows a brown, sunken lesion or dead area, lighter in color than the stalk lesion caused by black shank. The dead area is stingy, and the outer layer of stalk often has a papery consistency. |
| 1440035 |
Tobacco Vein Mottling Virus |
Potyvirus TVMV |
The initial symptom of TVMV infection is a slight, barely visible clearing on expanding leaves. Subsequently, leaves develop irregular green patterns of mottling adjacent to the veins; this is most evident on the ruffles at the base of older leaves. Chlorosis of infected leaves is extensive, giving the plants a pale green or yellow appearance which may be evident from a distance. Necrotic spotting of the leaf, indistinguishable from weather fleck, may develop and become increasingly prevalent as plants mature. The earlier that plants are infected with the virus, the greater the damage. The virus overwinters in perennial solanaceous weeds and is transmitted to tobacco by aphids. The virus is often found in combination with TEV. TVMV is also one of the most prevalent viruses in burley. |
| 1440036 |
Tobacco Vein Mottling Virus |
Potyvirus TVMV |
The initial symptom of TVMV infection is a slight, barely visible clearing on expanding leaves. Subsequently, leaves develop irregular green patterns of mottling adjacent to the veins; this is most evident on the ruffles at the base of older leaves. Chlorosis of infected leaves is extensive, giving the plants a pale green or yellow appearance which may be evident from a distance. Necrotic spotting of the leaf, indistinguishable from weather fleck, may develop and become increasingly prevalent as plants mature. The earlier that plants are infected with the virus, the greater the damage. The virus overwinters in perennial solanaceous weeds and is transmitted to tobacco by aphids. The virus is often found in combination with TEV. TVMV is also one of the most prevalent viruses in burley. |
| 1440018 |
blue mold |
Peronospora tabacina |
Blue mold may occur on the plant anytime from seedling to harvest; however, young tissue is more susceptible than old tissue. The first evidence of blue mold in the field usually occurs on the leaves as yellow circular spots about the size of a nickel. The spots soon develop the characteristic bluish, downy fungal growth on the undersides of the leaves which is best seen in the morning when the leaf is wet. If spots develop on leaves that are expanding, a puckering of the leaf occurs. As spots age, they turn from yellow to tan or brown and often tear or drop out. If infection has occurred near or on a leaf vein, a localized systematic infection may occur. The affected vein becomes reddish-brown, and the area around the vein is yellowed and distorted. In newly set transplants, it is possible for the fungus to develop systematically, killing the main bud and resulting in stunting or death of the plant. Splitting the stalk of systematically infected plants reveals a reddish- brown discoloration in the vascular tissue beneath the epidermis. A one-sided systemically infection also occur, resulting in a deformed stalk and lodging of affected plants. During weather favorable for blue mold (cool, cloudy, and wet), the disease can develop rapidly, causing numerous leaf lesions which can result in leaf blighting and severe leaf loss. The disease may develop during hot, humid periods if cool nights exist. |
| 1402051 |
black root rot |
Thielaviopsis basicola |
This fungal disease is associated with high soil pH. In the plant bed, irregular areas of seedlings turn pale green to yellow. Roots may be severely blackened, rotted or pruned, or they may have only a few lesions near the tap root. Damping-off can occur if the rot extends up the stem. In the field, infected plants in circular areas turn pale, are stunted, and flower prematurely. They wilt in the heat of the day but recover at night. Small roots may be rotted at the tips; larger ones have rough sunken black lesions along their length. Root pruning is common. If the weather turns warm before rot becomes extensive, new roots will form and plants will recover. Symptoms may be confused with those due to drowning, lesion nematode, or black shank. |
| 1402030 |
Potato Virus Y |
Potyvirus PVY |
Mild symptoms of this virus disease include leaf mottling and crinkling, prominent veins, and curved midribs. Leaf tissue, except for that around the veins, turns slightly yellow in color. This gives the veins a green-banded appearance. As the leaves mature, sunken brown spots may develop on the upper surface of the midrib. Systematic necrosis frequently occurs in cultivars resistant to root-knot nematodes. As lower leaves begin to ripen, midribs may turn black; leaves may die and fall from the stalk. If the stalk is split, areas of black discoloration will be found extending from top to bottom of the plant. |
| 1402044 |
Fusarium wilt |
Fusarium oxysporum f.sp. nicotianae |
This fungal disease causes slow yellowing and drying of the leaves. Symptoms are usually more pronounced on one side of the plant. Leaves may not wilt at first, but those on affected sides of the plants are usually stunted. The top of the plant may be drawn toward the diseased side. Wilting eventually occurs and upper leaves have a bronze cast. On the affected side of the plant, wood beneath the outer bark has a uniform chocolate brown discoloration. Such discoloration can also be seen in the midribs of affected leaves and in roots. Some roots on the affected side die. The unilateral appearance of symptoms and vascular discoloration can cause confusion between Fusarium wilt and Granville wilt. However, the "bacterial streaming" described for Granville wilt is a reliable way to distinguish between these two diseases. Fusarium wilt is frequently accompanied by root-knot nematode infection. |
| 1440032 |
Tobacco Etch Virus |
Potyvirus TEV |
The first symptom of TEV infection is a pronounced vein clearing on expanding leaves. This is followed by necrosis of a thin line of tissue along the veins, resulting in an etched pattern. Subsequently, young leaves develop a mosaic which fades to mottling as the leaf ages. Etching and more pronounced veinal necrosis is common. Plant growth is retarded, resulting in stunting, especially when young plants are infected. The virus overwinters in perennial solanaceous weeds and is transmitted to tobacco by migrating aphids. TEV often occurs in combination with other aphid-borne viruses. Tobacco etch is one of the most common virus diseases of burley. |
| 1440041 |
Alfalfa Mosaic Virus |
Alfamovirus AMV |
The most distinguishing symptom of alfalfa mosaic virus is a bright yellow mosaic of the affected leaves, however, not all strains of the virus produce this symptom. Chlorotic line patterns similar to the symptoms of tobacco ringspot are common. Chlorotic blotches and vein clearing of expanding leaves are often present. The virus overwinters in legumes and is transmitted to tobacco by aphids. AMV is found infrequently in burley. |
| 1402028 |
Potato Virus Y |
Potyvirus PVY |
Mild symptoms of this virus disease include leaf mottling and crinkling, prominent veins, and curved midribs. Leaf tissue, except for that around the veins, turns slightly yellow in color. This gives the veins a green-banded appearance. As the leaves mature, sunken brown spots may develop on the upper surface of the midrib. Systematic necrosis frequently occurs in cultivars resistant to root-knot nematodes. As lower leaves begin to ripen, midribs may turn black; leaves may die and fall from the stalk. If the stalk is split, areas of black discoloration will be found extending from top to bottom of the plant. |
| 1402037 |
Phytophthora blight |
Phytophthora nicotianae |
The black shank fungus can infect tobacco plants of any age. In young seedlings, stems may decay near the soil surface and the root system may become partly or completely black. A dark lesion may extend up the stem. Symptoms are sometimes confused with damping-off caused by other organisms. The photo above shows black shank damage as it appears in the field. Leaves may suddenly and uniformly wilt or droop, turn yellow, and hang down the stalk. Warm, moist weather conditions favor black shank development. Advanced stages of this disease may cause partial or complete decay of the root system. The black shank fungus is soil-borne and is readily translocated by equipment or water movement to noninfested areas. Since the spores of the fungus are so mobile, distribution of the disease within a field may not be uniform. |
| 1402038 |
Phytophthora blight |
Phytophthora nicotianae |
Stalks generally develop black lesions which may extend several inches above the ground |
| 1402032 |
Tobacco Etch Virus |
Potyvirus TEV |
Symptoms vary depending on the strain of the virus present and the conditions of plant growth. Veinclearing (lightening of the tissue in and around veins) is followed by a faint, light-green mottling of the leaf. This mottling is similar to that observed with tobacco mosaic; but with etch, the blotches are much less pronounced. Older infected leaves may show a stippled pattern of numerous, small, white flecks and fine lines (etchings), especially along veins. |
| 1440004 |
Pythium diseases |
Pythium spp. |
Damping-off affects tobacco at any stage of growth in the plant bed. The disease first appears as irregular areas of wilted, yellowed, stunted, or dead plants. These symptoms are the result of girdling of the lower stem of the tobacco plants by either Rhizoctonia or Pythium fungi species.Pythium usually affects the young tobacco plant near the soil line. A soft, brown, watery rot girdles the stem, causing the plants to fall over. Plants affected after stems harden may not die but turn yellow due to injury to the stem and root system. Pythium sometimes attacks transplants shortly after they are set in the field, causing a stem rot. |
| 1402005 |
Pythium diseases |
Pythium spp. |
Soil-borne fungi are the main cause of damping-off. Symptoms first appear on the stem of seedlings as a brown to black rot. The decay extends up the stem and causes the seedlings to collapse. Roots of affected plants may remain healthy. Seedlings die in patches. |
| 1440061 |
houseburn |
|
Houseburn is also known as pole rot, barn rot, pole sweat, shed burn, vein rot, and stem mold. Symptoms include white mold on midveins, odor of rotting tobacco, and partial decay caused by several species of fungi and bacteria. Freshly harvested tobacco is not highly susceptible, but damage may begin when the cure progresses through the yellowing stage and portions of the leaf begin to die. Injury occurs when microorganisms attack leaves that become moist during periods of high humidity lasting longer than 24 hours. Damage is measured in weight loss and lowered leaf quality and can range from mild to severe. Conditions which favor harvest of immature tobacco and prolonged leaf wetness in the barn will encourage houseburn |
| 1402024 |
brown spot |
Alternaria alternata |
This fungal disease appears first on the older leaves as circular, brown spots (1/4 to 1 1/4 inches in diameter) with sharply defined margins. Concentric circles (rings) are often noticeable within the spots. As the leaves approach maturity, a yellowish "halo" of varying width often forms around the lesion. Lesions may merge, forming large areas of dead tissue. During humid weather, sporulation of the fungus may be abundant, giving the lesions a black, dusty appearance. Brown spot is most severe as the plant approaches maturity, and the disease progresses from the lower to the upper leaves. Disease severity depends much on the weather, the overall health of the plant, varietal tolerance, and harvest rate. |
| 1440019 |
blue mold |
Peronospora tabacina |
Blue mold may occur on the plant anytime from seedling to harvest; however, young tissue is more susceptible than old tissue. The first evidence of blue mold in the field usually occurs on the leaves as yellow circular spots about the size of a nickel. The spots soon develop the characteristic bluish, downy fungal growth on the undersides of the leaves which is best seen in the morning when the leaf is wet. If spots develop on leaves that are expanding, a puckering of the leaf occurs. As spots age, they turn from yellow to tan or brown and often tear or drop out. If infection has occurred near or on a leaf vein, a localized systematic infection may occur. The affected vein becomes reddish-brown, and the area around the vein is yellowed and distorted. In newly set transplants, it is possible for the fungus to develop systematically, killing the main bud and resulting in stunting or death of the plant. Splitting the stalk of systematically infected plants reveals a reddish- brown discoloration in the vascular tissue beneath the epidermis. A one-sided systemically infection also occur, resulting in a deformed stalk and lodging of affected plants. During weather favorable for blue mold (cool, cloudy, and wet), the disease can develop rapidly, causing numerous leaf lesions which can result in leaf blighting and severe leaf loss. The disease may develop during hot, humid periods if cool nights exist. |
| 1440030 |
Tobacco Ringspot Virus |
Nepovirus TRSV |
Tobacco ringspot has the most distinctive symptoms of the virus diseases. The name truly describes the disease because chlorotic or necrotic rings occur in the leaf. A concentric line pattern of chlorotic and necrotic tissue, often forming an "oak leaf" pattern, is very common. The symptoms occasionally are confirmed to one side of the plant. The disease appears early in the season, usually with initial growth after transplanting. Most infected plants recover as new symptomless leaves develop. The virus is transmitted by nematodes. In the field, infected plants may appear alone or clustered. Ringspot may occur in the plant bed. |
