List of pests and diseases

Alfalfa MosaicTypical leaf symptoms on plants with alfalfa mosaic include bright yellow blotches with some mottle. Leaves eventually develop a bronze discoloration. Internally, phloem tissue becomes necrotic, including the phloem in the roots. The disease usually causes plant death. One of the most striking symptoms is the necrotic rings and spots on the fruit. Some fruit may develop a solid brown necrosis over the surface.
Alternaria Stem Canker Symptoms of Alternaria stem canker appear on stems, leaves, and fruit. Dark brown to black cankers with concentric zonation occur on stems near the soil line or aboveground. Cankers enlarge, girdle the stem before harvest, and kill the plants. Vascular tissue about 2 inches above and below the cankers exhibit brown streaks. Dark brown to black areas of dead tissue between leaf veins are caused by a toxin produced by the fungus. Dark brown sunken lesions with characteristic concentric rings develop on green fruit either on plants or during transit.
Andean mottle of potatoyellow local lesions or blotches, mild or severe mottle some leaf malformation.
Andean Potato latent virus"the virus was latent in most isolate/cultivar combinations with primary infection but secondary infection commonly caused symptoms. Wild species infected with the different isolates normally reacted with symptoms with either type of infection. The main symptoms were mosaics, chlorotic netting of minor leaf veins and, with wild species, leaf deformation; the netting symptom was typical only with Caj. In infected cultivars growing in the field, an additional symptom, rugosity, sometimes also developed and environmental conditions at high altitude seemed to enhance symptom formation. Very severe symptoms were found in a cultivar jointly infected with APLV and Andean potato mottle virus. Transmission of APLV from an infected plant to its tubers was erratic."
Annular leaf spot of potatoSmall round leaf spots are formed, with pronounced concentric ridges on the upper side. Lesions are rather similar to those caused by Alternaria solani, but they are not depressed. They are typically brown rather than black. With the help of a good magnifying glass, the relatively large black pycnidia may be observed on the upper side of lesions. In a more advanced stage, leaves become scorched and susceptible to wind damage. Leaf tissues finally become necrotic and leaves are dropped.
Anthracnose of tomatoAnthracnose of tomatoes is primarily a disease of ripe and overripe fruit. Depressed, circular lesions about 0.5 inch (1.2 cm) in diameter appear on ripe fruit. With age the lesions become tan and dotted with small black specks (microsclerotia). During moist weather, masses of salmon-colored spores may form on the lesion surface. Infection may also occur on stems, leaves, and roots. Root infections (called black dot root rot) become evident when fruit begin to ripen. Root lesions are brown and dotted with microsclerotia. The cortex of infected roots is often completely rotted.
Bacterial BlightLeaf lesions begin as light yellow spots. They expand and become brown and water-soaked with yellow halos. Affected tissue eventually turns black. Young leaves turn black and die quickly. Lesion expansion occurs slowly on older leaves. Affected leaves may also exhibit black streaks along midribs and veins. Leaves displaying this symptom may al be crinkled along the midvein or margin. Petioles and stems may be girdled by black lesions and the tissue beyond this point withers and dies. Tissue directly affected by syringomycin turns black and exhibits water-soaking while those that die as a result of girdling turn brown. Dead shoots bend, forming a shepherd's crook. Twigs that become woody before infection occurs have lesions comprised of black streaks that run lengthwise. Flower clusters often blight rapidly when infected and turn black. The rest of the inflorescence turns dark brown and limp.
Bacterial canker of tomato"There are usually no symptoms of bacterial canker on seedlings; however, on young plants symptoms consist of poor growth and temporary wilting of branches. Lower leaves yellow and shrivel, but symptoms may not show until flowering. On mature plants there are two kinds of symptoms, those resulting from systemic infections (i.e., the bacteria enter the vasculature and invade much of the plant) and those resulting from secondary infections (i.e., the bacteria cause local infections of leaves, stem, and fruit).In systemic infections of mature plants, leaflets of the oldest leaves curl, yellow, wilt, and finally turn brown and collapse (known as firing). Sometimes, one side of a leaf is affected. Plants grow poorly and wilt. Pith of stems becomes yellow and later reddish brown, especially at the nodes, and has a mealy appearance. The pith may later become somewhat hollow. In advanced infections, cankers may or may not form at the nodes. Light and later dark streaks may develop on stems. Branches break off easily. Plants may die.In secondary infections, infection of the margins of leaves is common. Lesions are dark brown to almost black. Round to irregular spotting of leaves also occurs. Fruit may be spotted, especially near calyx. On fruit bacterial canker symptoms appear as yellow to brown spots, slightly raised, surrounded by a persistent white halo (""bird's eye spot""). Spots are usually about 0.125 inch (3 mm) in diameter. Vascular tissue under the calyx scar and leading to seeds that may be brown."
Bacterial Ring Rot of potatoFoliar symptoms of bacterial ring rot generally appear at mid-season or later. Yellow areas develop on leaf margins or between veins and later turn brown, giving the leaves a burned appearance. Plants with advanced symptoms show vascular discoloration and milky, viscous bacteria may be forced from cut stems. In tubers, symptoms may occur before harvest or in storage. Rot begins as a brown necrosis in the vascular ring and progresses to surface. Cracks may appear on surfaces of tubers, which are frequently nothing more than hollow shells.
Bacterial Soft Rot of potatoSymptoms of soft rot include rotted tissues that are wet, cream to tan in color, and soft. Rot begins on the tuber surface and progresses inward. Infected tissues are sharply delineated from healthy tissue by dark brown or black margins. Shallow necrotic spots on the tubers result from infections through lenticels. Rotting tissue is usually odorless in the early stages of decay, but develops a foul odor as secondary organisms invade infected tissue. Soft rot can also infect wounded stems and roots.
Bacterial Speck of tomatoBacterial speck appears as dark brown to black lesions of various sizes and shapes on leaves, fruit, and stems. Tissue adjacent to the lesions is initially yellow. Leaf lesions are frequently concentrated near margins, causing extensive marginal necrosis (tissue death). Lesions on immature fruit are slightly raised and small, varying in size from tiny flecks to 0.125 inch (3 mm) in diameter and cause raised black spots on mature fruit. Fruit lesions are superficial, seldom penetrating more than a few cells deep.
Bacterial spot of tomatoBacterial spot develops on seedlings and mature plants. On seedlings, infections may cause severe defoliation. On older plants, infections occur primarily on older leaves and appear as water-soaked areas. Leaf spots turn from yellow or light green to black or dark brown. Older spots are black, slightly raised, superficial and measure up to 0.3 inch (7.5 mm) in diameter. Larger leaf blotches may also occur, especially on the margins of leaves. Symptoms on immature fruit are at first slightly sunken and surrounded by a water-soaked halo, which soon disappears. Fruit spots enlarge, turn brown, and become scabby.
Bacterial wilt of potatoThis disease occurs in scattered plants or groups of plants. The initial symptom is wilting of terminal leaves, followed in 2-3 days by a sudden and permanent wilt. Adventitious roots may develop on the main stems. Additional symptoms include vascular browning, water soaking of pith followed by browning, and in later stages browning of cortex near the soil line. Bacteria streaming can be seen when a freshly cut stem is suspended in water.
Beet cyst nematodeEntire fields can be infested, or localised infection can appear as circular or oval areas where plant stand and growth are poor. Over time, the smaller areas of infestation will enlarge and spread. Beet cyst nematode can infect plants of all ages. Seedling attack can result in severe injury or even plant death. When older plants are attacked, less damage will occur. Above-ground symptoms consist of reduced stand, poor growth, stunting, yellowing and wilting Roots attacked by beet cyst nematode appear ?bearded? or ?whiskered? due to the excessive development of fibrous roots. Root vegetables will have smaller storage roots which may have abnormal swellings. The most evident sign of beet cyst nematode is the appearance of glistening white-yellow bodies about the size of a pin head attached to the fibrous roots
black blight of potatocauses a leaf spot disease superficially similar to that caused by Alternaria solani, but the affected tissues are not depressed. Lesions are typically blackish rather than brown. Microscopically, light- coloured pycnidia (diameter 125-200 ?m) can be seen embedded in the affected tissue. Only the ostioles emerge through the epidermis. In later stages of infection, numerous small lesions may coalesce, so that leaves turn blackish and appear scorched.
Black Dot of potatosilvery lesions on the tuber surface which result in a deterioration in skin quality. In addition to causing tuber blemish symptoms, C. coccodes also causes symptoms on stems and foliage, resulting in crop losses in some countries, and is implicated as a factor in the potato early dying disease complex.
Black mold of tomatoBlackmold is characterized by obvious lesions that appear on the surface of ripe fruit. Lesions are light to dark brown and vary from small flecks affecting only epidermal tissue to large, more or less circular, sunken lesions with decay extending into the carpel wall and often into the seed locule. During warm, humid weather the fungus may sporulate to form a black, velvetlike layer on the surface of the sunken lesions.
Blackleg of oilseed rapeThe first obvious symptom of blackleg of oilseed rape (rapeseed) (Brassica napus, B. rapa, and some other Brassica spp.) caused by the fungus Leptosphaeria maculans, is the appearance of gray-green to ash-gray lesions on the lower leaves. The presence of small, black pycnidia at the edge or scattered across the blackleg lesions distinguishes them from lesions caused by another common foliar pathogen, Alternaria brassicae.
Blackleg of potatoPlants with blackleg are stunted and have a stiff, erect growth habit. Foliage becomes chlorotic and the leaflets tend to roll upward at the margins. Stems of infected plants exhibit an inky black decay. The base of the stem is often completely rotted. In relatively dry soil, only the pith may show blackening. Tuber symptoms for blackleg are similar to those of soft rot. The soft rot Erwinia spp. may cause symptoms similar to blackleg but lack the characteristic inky black decay.
Brown RotThe eyes of infected potato tubers turn grey or brown and exude bacterial slime which soil particles adhere to. The sticky bacterial ooze may also occur around the area where the tuber is attached to the stolen.
Brown wheat rust of potatoSmall brown pustules develop on the leaf blades in a random scatter distribution. They may group into patches in serious cases. Infectious spores are transmitted via the soil. Onset of the disease is slow but accelerated in temperatures above 15?C, making it a disease of the mature cereal plant in summer, usually too late to cause significant damage in temperate areas. Losses of between 5 and 20% are normal but may reach 50% in severe cases.
CalicoCalico symptoms on potato appear as pale to bright yellow or blotching of leaves. Some strains cause severe stunting and necrosis of stems and tubers. Dry, corky areas or rusty brown patches develop within tubers.
Cereal cyst nematodeCereal Cyst Nematode (CCN, Heterodera avenae) is a pest of graminaceous crops worldwide. This nematode is a significant problem across eastern Australia, and is detected in the Northen and Central regions of Western Australia. CCN becomes more problematic in areas where intensive cereal cropping occurs. CCN will only infect, feed and develop on cereals and other grasses (particularly wild oat). Non-cereal crops will not host the nematode, so are useful in rotations to limit damage caused to cereals.
Common rust of maizeis a disease that frequents corn fields nearly every year. However, infections and associated corn grain yield loss are usually very minimal. Infection normally occurs from late-May to early-July. Common rust has cinnamon-brown colored round to elongated pustules that frequently form in bands on the lower part of the leaf, which result from infection when the leaf was in the whorl. Common rust pustules form on both upper and lower sides of an individual leaf, distinguishing Common from Southern rust, which predominately sporulates on the upper leaf surface. Common rust development requires relatively cool to moderate temperatures (54 to 82 degrees F) and nearly 100% relative humidity for about six hours. Rust development is much more likely in pre-tassel stage corn, because a large whorl provides a humid, protected environment, and young leaf tissue is more susceptible to infection than emerged leaves. After tasseling, all leaves are completely emerged (past whorl stage) and should be relatively immune to further common rust development.
Common Scab of potato"Tuber symptoms of common scab vary in extent and appearance. Common scab lesions are usually circular and 0.25 to 0.33 inch (6 to 8 mm) in diameter, but they can be smaller in early stages of development and larger if they coalesce. Lesions typically possess a raised margin and slightly depressed center. Some characteristic symptoms have descriptive names: russet scab appears on tubers as superficial tan to brown corky lesions; pitted scab is characterized by lesions with depressions beneath the tuber surface; and raised scab appears as cushionlike, warty lesions. Common scab lesions can be confused with tuber lesions of powdery scab caused by Spongospora subterranea and patchy russetting caused by Rhizoctonia solani. In addition to tuber symptoms, Streptomyces spp. can cause brown stem and stolon lesions."
Corky Root Rot of tomatoinfected roots of plants with corky root rot are distinctly corky. Extensive brown lesions, often arranged in bands with lengthwise cracking of the cortex, develop on the larger roots. The tips of infected older roots are pinched off. Small feeder roots may be completely decayed. Infected plants are stunted and slow growing. Branches on mature plants may die back from the tips.
Cottony soft rot Sclerotinia stem rot first appears as watersoaked spots, usually at the point where stems attach to branches, or on branches or stems in contact with the soil. A white cottony growth of fungal mycelium develops on the lesions, and infected tissue becomes soft and watery. The fungus may spread rapidly to nearby stems and leaves if moisture is present for several hours. Lesions then may expand and girdle the stem, causing the foliage to wilt. During dry conditions, lesions become dry and will turn beige, tan, or bleached white in color and papery in appearance. Hard, irregularly shaped resting bodies of the fungus, called sclerotia, form in and on decaying plant tissues. Sclerotia are generally 1/4 to 1/2 inch in diameter, initially white to cream in color but become black with age. They frequently develop in hollowed-out centers of infected stems. Sclerotia eventually fall to the ground where the fungus is able to survive until the next growing season.
Cucumber Mosaic VirusCucumber mosaic appears as a chlorosis and blistering mottle of leaves. Margins of leaves are wavy. Intense yellow flecks may develop over the leaf surface. Plants are stunted.
Cucumber mosaic virus disease of tomatoSymptoms on plants infected with cucumoviruses can vary. Generally, plants appear lighter in color and are bushy and stunted. Close up symptoms include a mosaic (alternating light and dark green areas) on at least some leaves, especially on the younger leaves. Leaves may exhibit a shoestringlike appearance. Fruit production is greatly reduced. These symptoms can be confused with those caused by tobacco mosaic virus.
Curly Top of PotatoCurly top symptoms include dwarfing, yellowing, and rolling of upper leaves. Leaves near the growing point develop yellow margins and become twisted and cupped. Veins of outer leaflets remain green while the rest of the leaflet turns yellow. Aerial tubers may form.
Curly Top of TomatoPlants with curly top are stunted because growth ceases. Plants turn yellow to bronze in color with purple-tinged leaves. Plants become stiff and soon die. Green fruit turns red, regardless of age.
Deforming mosaic of potatoSymptoms of mosaic with leaf distortion were seen in infected potato plants and a virus was suggested as the causal pathogen. In this study, we have characterised the causal agent of this disease by transmission experiments and molecular analysis of the viral genome.
Deforming Rust of PotatoDeforming rust, infection of leaves and petioles of potato
Didymella Stem RotBrown clear-cut lesions occur at different levels along the stem, usually at soil level and show characteristic dark dots (pycnidia).
Downy mildew of cucurbitsDowny mildew first appears as small, pale green to yellow, angular spots delimited by leaf veins that give the foliage a mottled appearance. Eventually the spots coalesce and the leaf will turn brown. During moist weather, the lower surface of the leaf may be covered with a white to purple growth. Older leaves become infected first.
Downy mildew of lettuceDowny mildew causes light green to yellow angular spots on the upper surfaces of leaves. White fluffy growth of the fungus develops on the lower sides of these spots. With time these lesions turn brown and dry up. Older leaves are attacked first. Severely infected leaves may die. On rare occasions the pathogen can become systemic, causing dark discoloration of stem tissue.If downy mildew infects the cotyledons of young seedlings, the plants can die. Greenhouse grown lettuce transplants can also be infected.
Downy mildew of mellonDowny mildew first appears as small, pale green to yellow, angular spots delimited by leaf veins that give the foliage a mottled appearance. Eventually the spots coalesce and the leaf will turn brown. During moist weather, the lower surface of the leaf may be covered with a white to purple growth. Older leaves become infected first.
Downy mildew of sunflowerDowny mildew occurs in sunflower when 2-3 inches of rain occur within two to three weeks of planting. The only control for downy mildew has been to use Apron treated seed. Downy mildew is common in many fields, especially where heavy rains has occurred shortly after planting. Plants with systemic downy mildew are recognized by the stunted plants, yellow symptoms on the main veins and a downy white growth on the lower surface of the main veins. Occasional plants with systemic infection do not result in yield losses since nearby plants compensate in yield. When large areas of plants have systemic infection, then yield loss occurs.
Dumping-off of tomatoSeedlings affected by damping-off fail to emerge or fall over and die soon after emergence. Stems usually have a dark, shriveled portion at the soil line. Damping-off is generally limited to areas where drainage is poor or where soil is compacted, but whole fields can be affected, especially in early plantings exposed to rain.
Early blight of PotatoEarly blight is primarily a disease of stressed or senescing plants. Symptoms appear first on the oldest foliage. Affected leaves develop circular to angular dark brown lesions 0.12 to 0.16 inch (3-4 mm) in diameter. Concentric rings often form in lesions to produce characteristic target-board effect. Severely infected leaves turn yellow and drop. Infected tubers show a brown, corky dry rot.
Early Blight of Tomato"Plants infected with early blight develop small black or brown spots, usually about 0.25 to 0.5 inch in diameter, on leaves, stems, and fruit. Leaf spots are leathery and often have a concentric ring pattern. They usually appear on older leaves first. Spots on fruit are sunken, dry, and may also have a concentric pattern; frequently they occur near the calyx end of the fruit."
False Root Knot NematodeNematodes in the genus Nacobbus produce galls that are similar in appearance to those caused by root-knot nematodes. If diagnosis is primarily based on field symptoms, it is often erroneously assumed that crop damage caused by Nacobbus species is due to Meloidogyne species. For this reason, Nacobbus species are referred to as false root-knot nematodes.
Flax rustRounded orange-yellow pustules develop on seedlings about mid-season. In summer, orange pustules develop on the leaves. In late summer, brown to black pustules develop on the leaves; on stems they are elongated and purplish black. Bolls break off or fail to develop.
Fusarium Crown and Root Rot of tomatoFoliar symptoms on plants with Fusarium crown and root rot include yellowing along the margin of the oldest leaves, followed by necrosis. Dry brown lesions develop in the cortex of the tap or main lateral roots. A necrotic lesion may also develop on the surface of the stem from the soil line to 4 to 12 inches (10?30 cm) above it. Internally, a reddish brown or chocolate-brown discoloration extends no more than 6 to 12 inches (15?30 cm) above the soil line. Infected plants may be stunted and wilted, and older plants may die.
Fusarium Dry Rots of potatoFusarium dry rot causes a dry rot of infected tubers, although a moist rot may occur if secondary infection by soft rot bacteria is also involved. Initially, lesions appear as brown to black flecks on the tuber surface. Lesions later form large, hollow cavities. Frequently, the lesions appear wrinkled on the tuber surface with numerous white tufts of mycelium. Infected seed pieces may completely decay.
Fusarium Foot Rot of tomatoFusarium foot rot causes varying degrees of interveinal chlorosis and necrotic spotting on young foliage. Foliar symptoms may be similar to certain viruses (tomato spotted wilt or alfalfa mosaic). Flowers are often necrotic. Aboveground symptoms may be restricted to single branches. In severe cases, plants die. A dark brown lesion, about 0.5 to 1 inch (1?2.5 cm) long, is visible on the tap root or a main lateral root. Often the lesion completely girdles the root. The lesion usually occurs on the roots within the top 12 inches (30 cm) of soil. Internally, a brown discoloration of the vascular system extends 1 to 4 inches (2.5?10 cm) from the lesion.
Fusarium WiltThe Fusarium wilt fungus infects plants through the rootlets, invading the xylem and eventually extending throughout the plant. Individual branches and associated leaves on plants infected with Fusarium become yellow and wilt. Sometimes only one branch or one side of the plant is affected, creating a yellow flag effect. Infected plants usually die. A dark brown vascular discoloration extends far up the stem. Symptoms often first appear during fruit sizing.
Gray Mold of tomatoGray mold appears on young plants as gray-brown velvety mold covering stems or leaves. Infections that girdle the stem cause wilting above the infected area. In the field gray spores cover dying flowers and the calyx of fruit. Under a hand lens, the spore-bearing structures resemble bunches of grapes. Infections spread from flowers or fruit back toward the stem, which turns white and develops a canker that may girdle it.
Late Blight of potatoLate blight lesions can occur on all aboveground plant parts. On leaves, lesions typically first appear as small pale to dark green water-soaked spots that are irregular in shape and surrounded by a zone of yellowish tissue. Under conducive conditions, lesions expand rapidly and become brown to purplish black as tissue is killed. Under sufficient humidity, white sporulation of the fungus can be observed at the periphery of lesions, principally on the underside of leaves. On stems and petioles, lesions are brown to black and may also support sporulation of the fungus. Infected tubers develop a firm brown decay that starts on the outside and may later extend to include the outer 0.125 to 0.5 inch of tissues.
Late Blight of tomato"Leaf symptoms of late blight first appear as small, water-soaked areas that rapidly enlarge to form purple-brown, oily-appearing blotches. On the lower side of leaves, rings of grayish white mycelium and spore-forming structures may appear around the blotches. Entire leaves die and infections quickly spread to petioles and young stems. Infected fruit turn brown but remain firm unless infected by secondary decay organisms; symptoms usually begin on the shoulders of the fruit because spores land on fruit from above."
Latent mosaic of potatoSome strains of potato virus X produce no visible symptoms of latent mosaic, although yields may be reduced 15% or more when compared to virus-free plants. Other strains cause a mild mosaic with slight leaf crinkling under periods of low light intensity and low temperature (60? to 68?F). The additional presence of potato virus A or Y may cause crinkling, rugose mosaic, or browning of leaf tissue.
Leaf mould of tomatoDiffuse, pale, yellowish spots that become necrotic appear on the upper face of the leaves. Olive coloured, downy tissue develops on the underside of the leaflet which then yellows.
Leak of potatoLeak, also known as water rot, causes spongy, wet internal rot of tubers. The diseased flesh is clearly demarcated from healthy tissue by a dark boundary line. In advanced infections, hollow cavities form and all that remains of some infected tubers are tuber shells with thin papery skins.
Lesion nematodes of potatoThe symptoms described below are indicative of a nematode problem, but are not diagnostic because they could result from other causes as well. In general, aboveground symptoms include stunted, yellowed, chlorotic, and/or dead plants. Infected plants are likely to wilt earlier under temperature or moisture stress. Infestations may occur without causing any aboveground symptoms.Feeding by root knot nematode causes characteristic swellings, called galls, on roots. Galls caused by Meloidogyne chitwoodi are small and difficult to see. On heavily infested plants, egg masses appear as tiny round bumps on feeder roots. Meloidogyne hapla causes small distinct galls with proliferation of lateral roots around these galls. Meloidogyne incognita causes more pronounced galls. All three species of Meloidogyne and Pratylenchus penetrans cause bumps or warts on the surface of infected tubers. However, those caused by M. hapla are less distinct. Brown spots develop inside tubers, mostly in the outer 0.25 inch (6 mm), which are visible when a thin layer of tuber is peeled off. Lesion nematodes cause reddish brown lesions on the roots that turn black later. Stubby root nematodes cause numerous short and stunted (stubby) roots, and corky ringspot symptoms on tubers.
Maize leaf spotSpot-causing fungal disease occurring increasingly mainly in the cool region. The disease begins to occur around the rainy season and stripe lesions are produced along the midrib abundantly. Lesions are ash white with brown border, 0.5-3cm in length and 0.1-0.5cm in width. Lesions expand and fuse when occurring severely, and the infected leaf withers. The symptom in the picture is caused by race 3 of the pathogen, and the race is mainly occurring in Japan. Race 2 which produces short stripe is occurring a little, but no occurrences of race 1 which produces round lesions in specific corn lines have been reported in Japan.
Melon aphid diseaseAphids usually attack the growing shoots and expanding leaves. They feed on the lower surface of the leaves and injure the plants by sucking the sap. The leaves become deformed as they expand. They may curl down at the edges, and become wrinkled or puckered. Feeding on expanded leaves (more common with green peach aphid) may result in pale stippled areas of feeding damage between the veins. During heavy infestation, the vigour of the plant is greatly reduced, stunting growth of the plants. Leaves of such stunted plants are pale and may have yellow interveinal areas. Both species of aphid transmit several virus diseases in sweetpotato and in other crops. Infestation of the two aphid species could be differentiated by the production of the honeydew. M. persicae produces less honeydew than A. gossypii.
Mild Mosaic potatoInfection of Potato virus A appears as light yellow mottling with slight crinkling on potato plants with mild mosaic. Margins of affected leaves may be wavy, and leaves may appear slightly rugose (i.e., rough) where veins are sunken and interveinal areas are raised. Affected plants tend to open up because the stems bend outward. Severity of symptom expression depends on weather conditions, the potato cultivar, and the strain of virus A.
Phytophthora Root RotThe most distinctive symptoms of Phytophthora root rot are the brown lesions on roots of all sizes. The xylem of the roots above the lesions often turns yellowish or brown in color. In severe cases, nearly all roots may be girdled or rotted off. Aboveground, infected plants are slow growing and may wilt or die in hot weather. When fruit in contact with the ground are infected, the disease is called buckeye rot. Symptoms include tan or brown spots with concentric rings. Phytophthora capsici also causes greasy, purple-brown stem lesions.
Pink or brown eye of potatoPink eye is characterized by pink to brown blotches on the skin, usually around the eyes at the apical (bud) end of tubers. When the disease is severe, a shallow, reddish brown rot occurs beneath the discolored areas.
Pink root of potatoPink rot appears as a decay of tubers that usually begins at or near the stem end of potatoes in the field or through eyes of potatoes in storage. Infected tissue becomes somewhat rubbery but not discolored. When an infected tuber is cut, the rotted portion is delineated by a dark line at its margin. With exposure to air, the surface of the decay turns a salmon pink color, which later turns to brown and then finally black. Roots and lower stems may also rot, causing a wilt and early dying of plants. The spread of pink rot may continue in storage.
Potato aucuba mosaic virusChlorotic local lesions on older leaves, necrotic on younger, systemic (top) necrosis (Clinch, 1941). Stored tubers develop necrosis in the cortex and pith with irregular brown or sunken patches on the surface.
Potato leafroll Virus"The nature and severity of leafroll symptoms depend on the virus strain, potato variety, environment, and time and source of infection. Plants with chronic (seed tuberborne) infections are most severely affected. They typically are stunted and appear more erect. Lower leaves roll upwards at the margins, have a stiff leathery texture, and may die prematurely. In contrast, plants that become infected in the current season by aphid vectors of potato leafroll virus normally develop symptoms in the upper (youngest) leaves first; the leaves develop an upright orientation, become chlorotic, and roll upwards. Late-season infections are not always accompanied by symptoms. Potato leafroll virus can cause necrotic netting (net necrosis) in tuber vascular tissue of some varieties, including Russet Burbank."
Potato Mop-TopSpraing induced by PMTV results in unsightly internal brown lines and raised external rings on the tubers of sensitive potato cultivars but can cause symptomless infection in other cultivars.
Potato smutNo symptoms are visible above ground. Infected tubers are misshapen, or have warty swellings on the surface, and are hard. The whole or part of the tuber may be infected. Numerous brown-black specks, interspersed with lighter brown specks, occur in the flesh. The specks (spore sori) are about 1 mm in diameter and are filled with rusty brown spore balls. Infected tubers later become a dry brown powdery mass containing numerous spores. Galls resembling deformed tubers arise on the stems or stolons underground.
Potato Virus Msymptoms range from very slight (e.g. in cv. King Edward) to severe (e.g. in cv. Arran Victory). Causes mottles, mosaic, crinkling and abaxial rolling of leaves, and stunting of shoots.
Potato Virus Scauses few or no symptoms, but decreases yield of potato tubers by up to 20%
Potato Virus TMost plants primarily infected by PVT remain symptomless, but plants of potato cv. King Edward developed slight vein necrosis and chlorotic spotting, while cv. Cara showed top necrosis about 12 days after inoculation. Secondary infections are largely symptomless under glasshouse conditions.
Potato virus YMild 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.
Potato Y virus disease of tomatoSymptoms on plants affected by mosaic diseases can vary. In general, plants develop an overall lighter coloring and a bushy appearance. Close up symptoms include a mosaic (alternating light and dark green areas) on some leaves, especially the younger ones. Leaves may also be curled. Fruit may be distorted and develop mosaic symptoms. Internally, brown areas and necrotic areas develop and the fruit do not ripen normally.
Powdery mildew (barley)At first, powdery mildew can be observed as small greyish patches of fluffy fungal growth (mycelium) on the upper surface of the lower leaves. These spots resemble small cushions of white powder. Leaf tissue on the opposite side of an infected leaf turns pale green to yellow. The fungus only infects the epidermal layer and can be easily scrapped off with a fingernail. Infections can also occur on the leaf sheaths and ears. Leaves remain green and active for some time following infection, then gradually become chlorotic and die off. As the disease progresses, the mycelium often becomes dotted with minute black points (cleistothecia), which are the sexual fruiting bodies of the fungus.
Powdery Mildew Tomato"Leaves on infected tomato plants develop irregular, bright yellow blotches; severely affected leaves die but seldom drop. Spots of dead tissue, sometimes surrounded by a yellow halo, eventually appear in the blotches. There are no lesions on stems or fruit. Rarely, a gray mycelium develops on the lower leaf surface of infected leaves. Severe infections kill leaves and result in sunburn fruit and weakened plants."
Powdery scabTubers infected with powdery scab develop small purplish-brown pustules about 0.06 inch (1.5 mm) in diameter. The pustules typically become raised, brown, and wartlike as they enlarge to about 0.37 inch (9 mm) in diameter and rupture the tuber periderm. Powdery scab lesions on tubers may be confused with lesions of common scab, and laboratory confirmation of powdery scab is advised. Microscopic observation of mature powdery scab lesions typically reveals diagnostic dark brown spore balls of the causal fungus. In addition to tuber symptoms, S. subterranea causes galls on roots and stolons. Foliage symptoms have not been observed in California.
PYDVInfected plants are dwarfed and show typical yellowing and necrosis. Internal necrotic spots occur in stems, particularly in upper nodes. Pith necrosis of stems is common. Tubers are usually few, small and eformed with surface cracking and internal necrotic spots. Infected tubers hardly germinate. High temperatures favour and low temperatures delay ymptom development.
Rice blast diseasehe rice blast fungus may infect and produce lesions on most of the shoot but usually not the leaf sheath. From the seedling stage through plant maturity, rice blast progresses through several phases starting with leaf blast, followed by collar, panicle and node blast. Leaf Symptoms. Lesions that occur on the leaf are usually diamond-shaped with a gray or white center and brown or reddish brown border and are 0.39 to 0.58 inch (1.0-1.5 cm) long and 0.12 - 0.2 inch (0.3-0.5 cm) wide. Newly formed lesions may have a white or grey-green center and a darker green border. Their shape, color, and size can vary depending on varietal resistance, age of the plant, and lesion age. Leaf blast may sometimes cause the complete death of young plants up to the tillering stage. Leaf blast usually increases early in the season then declines late in the season as leaves become less susceptible. Leaf Collar Symptoms. Infection at the junction of the leaf blade and sheath results in the typical brown "collar rot" symptom. A severe collar infection may cause the leaf to die completely. Node Symptoms. Stem nodes may be attacked as the plant approaches maturity, causing the complete death of the stem above the infection. Diseased nodes are brown or black. Panicle and Grain Symptoms. Infections just below the panicle, usually at the neck node, cause a "neck rot" or "rotten neck blast" symptom that can be very injurious to the crop. If neck rot occurs early, the entire panicle may die prematurely, leaving it white and completely blank. Later infections may cause incomplete grain filling and poor milling quality. Other parts of the panicle including panicle branches and glumes may also be infected. Panicle lesions are usually brown, but may also be black.
Root and stem rot of soybeanPhytophthora can attack soybean plants at any stage of development. Symptoms in young plants include rapid yellowing and wilting accompanied by a soft rot and collapse of the root. More mature plants generally show reduced vigor and may be gradually killed as the growing season progresses. Foliar symptoms on older plants occur as general yellowing of the lower leaves that progresses upward on the plant, followed by wilting and death. The root system is usually severely affected such that lateral and branch roots are almost completely discolored. Tap roots show a brown discoloration on the surface and, if split, the inner tissues show a tan to brown discoloration. Perhaps the best diagnostic symptom of the disease on susceptible varieties is a lower stem discoloration that may extend several nodes up the stem.
Root Knot nematode"Mature female root knot nematodes are pear-shaped and about 0.01 inch long. Root knot nematodes spend most of their life in galls. Mature females resemble tiny, white pearls; they sometimes can be seen with the use of a hand lens when root galls are cut open."
Sclerotium Stem RotAffected stems on plants with sclerotium stem rot first show a moist decay at or slightly below the soil surface where infection is initiated. Stem lesions expand up and down the stem, and all plant parts can be infected. Stem infection leads to wilting and yellowing of the foliage. Tubers are typically infected by way of stolons. The fungus quickly grows over the tuber surface and invades, resulting in a moist cheesy decay. Portions of infected plant parts and nearby soil often are covered with the white, radiating mycelium of S. rolfsii. The mycelium generates small spherical sclerotia (about 1 to 2 mm in diameter) that are white when young and brown when mature.
Septoria Leaf Spot of tomato"Numerous, small, watersoaked spots, which are the first noticeable characteristic of Septoria leaf spot, appear on the lower leaves after fruit set. Spots enlarge to a uniform size of approximately 1/16 to 1/4 inch in diameter. They have dark brown borders and tan or light colored centers. Yellow haloes often surround the spots. Severely infected leaves die and drop off. Septoria leaf spot is easily distinguished from early blight, another foliar disease of tomato, by the uniform, small size of the spots and the lack of concentric rings in the spots; however, Septoria leaf spot is sometimes confused with bacterial spot of tomato. The presence of fruiting bodies of the fungus, visible as tiny black specks in the centers of the spots, confirms Septoria leaf spot."
Skin spot of potatoSkin spot is generally an invisible fungus until after approximately 2 months of storage, when the infected tissue begins to show spots. They tend to be bluish black and slightly raised. The mature fungal lesion is frequently sunken with a raised centre. Lesions may form either singly or in clumps and be distributed at random or aggregated around eyes, stolons and damaged skin. Infection can spread during storage.
Southern Blight of tomatoTomato plants with southern blight have lesions on the stem at or near the soil line. These lesions develop rapidly, girdling the stem and resulting in a sudden and permanent wilting of the plant. White mats of mycelia are produced on the stem and in the adjacent soil. In a few days, tan to brown spherical sclerotia about 0.06 inch (0.5 mm) in diameter appear on the mycelial mat. The abundant sclerotia are a good diagnostic feature.
Soybean mosaic virusoybean mosaic causes stunting of plants and crinkled and mottling of leaves. Infected plants range from no symptoms to severely mottled and deformed. The leaf blades are puckered along the veins and curled downward. The mottling appears as light and dark green patches on individual leaves. Symptoms can be difficult to see when temperatures are above 90?F. Do not confuse with growth regulator herbicide damage where the leaves will be elongated and which usually occurs in a pattern such as along a field edge. Soybean mosaic can also reduce seed size and pod number per plant, and soybean mosaic is one of several factors associated with discoloration of seeds, causing a dark discolored tear stain origination at the hilum. The virus can interact with bean pod mottle virus (BPMV) to create severe symptoms in plants infected with both viruses
Spindle tuber of potatosymptoms are often not visible during the first season when infection occurs, but become progressively more severe in the following generations. Infected plants are stunted and have an upright or erect appearance. The foliage may change colour, becoming either lighter or darker than normal and have smaller, distorted leaflets. Tuber symptoms are more obvious but do take several generations to appear. Affected tubers are small and deformed, becoming cylindrical and elongate ('spindle'). They are often pointed and can show growth cracking on larger tubers. Eyes will often become more prominent and sprouting is slower than with healthy tubers.
Stem and Stolon Canker of potatoAboveground symptoms of stem canker include uneven stands, weak shoot growth, and aerial tubers. Foliage may develop yellowing, purpling, and upward curling of leaves. Aboveground symptoms alone are not diagnostic, however, because other diseases can cause similar symptoms. On belowground stems and stolons, Rhizoctonia solani typically causes reddish-brown lesions that often develop into sunken cankers. Stolons can be girdled and killed, resulting in a pruning effect and malformation and abortion of tubers. If tubers in affected fields are left in the ground after vine death, they often develop black scurf, an accumulation of irregular black sclerotia of R. solani on the tuber surface.
Stem rust of cerealsThe stem rust fungus attacks the aboveground parts of the plant, infected plant produce fewer tillers and set fewer seed. In the case of extremely bad infection the plant may die. The site of infection is a visible symptom of the disease. Where infection has occurred on the stem or leaf, elliptical blisters or pustules called uredia develop
Sting nematodePlants damaged by sting nematodes often wilt, may be stunted and may show symptoms of nutrient deficiency. Seedlings may sprout from the soil and then cease growing altogether. Plant death may occur with high population densities of sting nematodes. On turfgrasses, damage usually shows up in irregular patches. Often, sting nematode damage to turf is accompanied by proliferation of weeds such as spurge, sedge or Florida pusley.
Stubby root nematode "Damage caused by P. minor usually occurs in irregularly shaped patches within a given field. Symptoms are usually more severe in sandy than in heavier soils. Above ground symptoms include; stunting, poor stand, wilting, nutrient deficiency, and lodging. Roots may appear abbreviated or ""stubby"" looking."
Syringae Leaf Spot"Brown-black leaf spots sometimes surrounded by chlorotic margin; dark superficial specks on green fruit; specks on ripe fruit may become sunken, and are surrounded by a zone of delayed ripening. Stunting and yield loss, particularly if young plants are infected. Reduced market value of speckled fruit. A. thaliana: Water-soaked, spreading lesions, sometimes surrounded by chlorotic margin"
Target leaf spot of tomatoSymptoms appear on all aboveground parts of the plant. Foliar lesions begin as small, pinpoint, water-soaked spots on the upper surface. Gradually these increase in size (up to 2 cm diameter), becoming circular,frequently ringed, and pale brown with conspicuous yellow halos. The lesions will coalesce leading to blighting of foliage. The subsequent premature defoliation affects fruit quality and yield. The lesions on stems and petioles are brown and World Vegetable Centoblong. These increase in size and may girdle petioles and stems leading to collapse of the leaflets.
Tobacco etch
Tobacco Mosaic VirusVein clearing appears in young, systemically-invaded leaves, 3-4 days post inoculation, followed by a light green-dark green mosaic, often accompanied by distortion and blistering. Inoculated leaves exhibit no symptoms other than faint chlorotic lesions when the plant nitrogen supply is limited. Plants may be stunted if they are infected while young.
Tobacco rattle virusAboveground symptoms of corky ringspot rarely occur. Symptoms in tubers vary depending on virus strain, potato variety, temperature, and time of infection. Symptoms include rings of dark brown corky layers in the tuber that alternate with rings of healthy tissue. Internally, small brown flecks are diffused through the tuber. This symptom can be confused with symptoms caused by alfalfa mosaic, which is often more common than corky ringspot.
Tobacco StreakDownward curling of leaf blades on tomato plants with tobacco streak is common. Leaf veins become necrotic and can lead to necrotic blotches, especially on young leaves. Fruit may develop necrotic ringspots. Necrotic streaks on young stems extend to flowers and leads to flower drop.
Tomato Big BudThe most striking symptom of tomato big bud is the large, swollen green buds that fail to develop normally and do not set fruit. Apical stems are thick and assume an upright growth habit. Infected plants appear bushy because of shortened internodes and small leaves. Leaves are distorted and yellow-green. Aerial roots may develop on stems.
Tomato Bushy StuntLeaves on plants infected with tomato bushy stunt virus are small in size, cupped, and curled downward. The youngest leaves are twisted and exhibit tip necrosis. A proliferation of lateral shoots leads to an overall bushy appearance. Lower leaves are chlorotic with a purple tinge. Plants may be stunted. Fruit yield is greatly reduced.
Tomato Infectious Chlorosis VirusThe leaves of infected plants become yellow or red between the veins, stunted, and rolled. Symptoms generally occur on older leaves, while new growth continues to appear normal. As the disease progresses, interveinal necrosis can occur and the leaves become characteristically brittle, thick, and crisp.
Tomato MottleThe leaves of infected plants become yellow or red between the veins, stunted, and rolled. Symptoms generally occur on older leaves, while new growth continues to appear normal. As the disease progresses, interveinal necrosis can occur and the leaves become characteristically brittle, thick, and crisp.
Tomato Pith NecrosisTomato pith necrosis affects mature tomato plants. Symptoms include a brown discoloration and/or necrosis of the pith, which eventually leads to hollow chambers in the stem. The pith browning usually extends far up the plant. Profuse adventitious roots are associated with the stem where the pith is affected. Gray or dark brown lesions may appear on the surface of the stem. Affected plants may turn chlorotic and wilt.
Tomato russet miteRusset mites are so small that a 14X hand lens is needed to see them. Because of their size, these mites are rarely noticed until plants are damaged. By this time, there may be hundreds of yellowish, conical-shaped mites on the green leaves immediately above the damaged bronzed leaves.
Tomato Spotted WiltPlants infected with tomato spotted wilt virus exhibit bronzing of the upper sides of young leaves, which later develop distinct, necrotic spots. Leaves may be cupped downward. Some tip dieback may occur. On ripe fruit chlorotic spots and blotches appear, often with concentric rings. Green fruit show slightly raised areas with faint, concentric zones.
Tomato Yellow Leaf CurlTomato plants infected with Tomato yellow leaf curl virus (TYLCV) are stunted, grow abnormally upright, and take on a bushy appearance because internodes are shortened.
TSWVPotato plants with TSWV may show dead (necrotic) spots or patches on the leaves. These can appear as concentric rings separated by green tissue, which may lead to confusion with target spot (early blight). Severely affected stems, and occasionally the whole plant, may die. Plants grown from infected tubers are severely stunted, with a rosette form of growth and dark green leaves.
Turnip crinkle virus
Verticillium wilt of PotatoVerticillium wilt becomes evident when lower leaves on the vine turn yellow and wither. Symptoms progress upward until the entire plant yellows and wilts. Vascular tissue of stems becomes a light brown, which is best observed near ground level. Some tubers from infected plants may develop a light brown discoloration in the vascular ring near the stem end. Wilt causes early senescence of plants in heavily infested fields.
Verticillium Wilt of TomatoOlder leaves on tomato plants infected with Verticillium appear as yellow, V-shaped areas that narrow from the margin. The leaf progressively turns from yellow to brown and eventually dies. Older and lower leaves are the most affected. Sun-related fruit damage is increased because of the loss of foliage. A light tan discoloration develops in the vascular tissue, especially near the base of the plant. The discoloration extends a short distance up the plant and may occur in patches. Symptoms are most noticeable during later stages of plant development when fruit begin to size.
Wart disease of potatoOnly the below ground symptoms are apparent. Rough, warty growths at the base of the stems. Eyes develop into warty, cauliflower-like outgrowths that can be cut more easily than the tuber. Growths are white below ground, green when exposed to light, and darken with age. The warts range from the size of a pea to large masses that cover the entire tuber.
Water mold of tomatoWater-soaked lesions develop on ripe fruit in contact with wet soil. Within several days, the entire infected fruit turns into a water bag.
White Mold of potatoWhite mold appears as water-soaked lesions covered by a white, cottony mycelial mat on leaves and stems. In severely affected plants, the stem is girdled and plants die. Hard, black, irregularly shaped sclerotia (about 0.25 to 0.5 inch in diameter) develop inside dying potato stems.
White rust of crucifers
Yellow potato cyst nematodeHost plant symptoms are not a reliable means of identification since symptoms of attack by Globodera species are not specific. Patches of poor growth may occur generally in the crop, sometimes with yellowing, wilting or death of foliage. Potato tubers may be small. Mild infestation symptoms suggest the plants may be under stress from water or mineral deficiency. On heavily infested plants the cysts on the roots are clearly visible with the naked eye. No tuber symptoms have been reported.