Melon Research Paper
Diseases of melon ( Cucumis melo ) in Arizona
Alternaria leaf spot
Alternaria leaf spot is caused by the fungus Alternaria. The fungus produces dark, multicelled spores on host tissue only when there is substantial moisture, usually during summer rains. The spores are easily carried in wind and splashing water and infect only the leaves. Brown necrotic spots appear on the leaves wherever spores germinate and infect leaf tissue (photo 1). Spots are small at first then may enlarge and coalesce to form circular lesions with visible concentric rings (photo 2).
Disease severity is dependent on varietal susceptibility and environmental conditions. Extended periods of moisture and warm temperatures favor disease development. It is rarely a problem …show more content…
in melons in the low desert in central or southwestern Arizona, but may be a sporadic problem in southeastern Arizona and in the Wenden-Aguila area.
Applications of fungicides, chlorothalonil or mancozeb, are preventive only, so fungicides should be applied regularly at the onset of summer rains to fields or plants in areas where disease is known to have occurred previously. 1 2
Charcoal rot
Charcoal rot is caused by a soil borne fungus, Macrophomina phaseolina. This fungus is common in Arizona soils, and causes disease in wide variety of plants. The fungus produces microsclerotia, small black structures that develop under the cortical tissue of roots or on the surface of stem lesions, that enable it to survive in the soil for many years in the absence of a host.
M. phaseolina has been associated with late season vine decline. It is most problematic in fall melons and is rare in spring melons harvested before mid June. In Arizona, it is often isolated from pink colored root lesions and from rotted roots. In drip irrigated systems, M. phaseolina also causes water-soaked lesions on the stems and crown (photo 1) that may have an gummy exudate in which case the disease looks very similar to gummy stem blight (photo 2). Vines with stem lesions have yellowing and death of leaves (photo 3). Fruit may also become infected, resulting in a firm, dark-colored decay.
There are no control measures currently recommended for charcoal rot. Cultural practices such as rotation, deep plowing and maintenance of soil moisture have not been effective. There has been little or no effective disease control using solarization or fumigation. Charcoal rot may be found in the same fields at the same time as Monosporascus vine decline, and control measures recommended for Monosporascus vine decline may also be beneficial in reducing charcoal rot (see Monosporascus vine decline).
1 2 3
iseases of melon ( Cucumis melo ) in Arizona
Downy mildew
Downy mildew of melons is caused by Pseudoperonospora cubensis. P. cubensis is a fungal-like organism that causes foliar necrosis and decline, and like other downy mildews, is an obligate parasite infecting only cucurbits. It does not affect the roots. Disease occurs on melons in the late summer and early fall during summer monsoon rains and in the late winter and early spring when there rain and heavy dew. With sufficient moisture in the foliage, disease progresses rapidly. P. cubensis produces spores that are carried by splashing water, wind and rain. Plants of all ages are susceptible.
Early infections cause yellow spots on leaves that coalesce, and the leaf turns brown. When humidity is very high, especially early in the morning, a white to light purple growth is visible on the underside of leaves, which consist of asexual spores. Older leaves are usually infected first. In areas where disease has been previously confirmed, it is important to watch for the initial symptoms and signs of disease so that fungicides can be applied as soon as possible. Protectant fungicides such as chlorothalonil and mancozeb should be applied in rotation with fungicides of other modes of action such as Gavel, Ranman, Previcur and Tanos. Repeat applications of fungicides may be necessary if conducive weather conditions persist. Alternating different chemicals is important to avoid development of resistance.
For more information, see the following web site: http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg13.htm http://www.ces.ncsu.edu/depts/hort/hil/hil-8.html
Diseases of melon ( Cucumis melo ) in Arizona
Monosporascus vine decline
Monosporascus vine decline is caused by the fungus Monosporascus cannonballus.
Plants may be infected when they are young, but symptoms usually do not appear until vines are mature and fruit are developing (photo 1). Foliage may have necrotic areas in the leaves and a progressive decline in the entire crown (photo 2). Tan lesions are often observed on roots, and, in the later stages of disease only, small black specks appear (photo 3). These specks are the sexual reproductive stage of the fungus that contain large black spores - thus the species name cannonballus (photo 4). These spores are commonly found in many different soils, and the fungus seems to be indigenous to certain semiarid …show more content…
soils.
There is no resistance in melons, but some varieties are much more susceptible than others. Caravelle and Desert Mark are among the most susceptible. The presence of spores in soils can be determined in laboratory assays, but to date there has been no direct correlation between the numbers of spores in soil samples and the incidence or prevalence of disease. Monosporascus vine decline becomes more problematic when melon crops follow one another without rotation. Disease may become so severe that planting melons that will mature in late summer and early fall is not economical.
Monosporascus vine decline can be reduced in drip-irrigated systems by more frequent applications of water when plants have a heavy fruit load. Soil fumigation with 1.3 dichloropropene (Telone II) and chloropicrin applied prior to planting and application of fludioxonil (Cannonball) or thiophanate methyl (Topsin-M) through buried drip irrigation beginning at plant emergence (see label instructions), may suppress disease. Lifting roots out of the ground immediately after the last harvest may reduce build up of inoculum (spores) in the soil.
1 2 3 4
Diseases of melon ( Cucumis melo ) in Arizona
Powdery mildew
Powdery mildew of melons is caused by Podosphaera xanthii (Sphaerotheca fuliginea). Disease is found anywhere cantaloupe, honeydew and other melons are grown in Arizona; it is favored by moderate to high humidity and low light intensity. A white powdery growth on the leaf surface starts out as small spots, often on the lower leaf surface, and gradually covers the entire leaf (photo 1). The mycelium of the fungus grows over the leaf surface and produces many asexual spores that are easily carried in the wind (photo 2). These spores germinate on the leaf surface where new infections develop within a few days. Advanced infections cause necrotic areas in leaves that can become extensive and result in a severe decline in foliage. Photosynthetic area is reduced and fruit exposed to sun burning. Variability in pathogenicity has been demonstrated in the fungus, and several races have been described based on host range. Podosphaera xanthii ( Sphaerotheca fuliginea) has two mating types which is probably why the sexual spores of the fungus are rarely found.
Registered fungicides used for control include sulfur dust and micronized sulfur; strobulurin fungicides azoxystrobin (Quadris), pyraclostrobin (Cabrio) and trifloxystrobin (Flint); thiophanate-methyl (Topsin-M); chlorothalonil (Bravo); quinoxyfen (Quintec); triflumizole (Procure); and mancozeb. Disease incidence may be reduced when foliar applications of neem extract (Trilogy) or potassium bicarbonate products (Armicarb 100, Kaligreen) are applied. Fungicides with the same mode of action such as the strobilurins should not be used in rotation with each other. Results of effective rotations and fungicide efficacy are available from yearly field trials in Yuma by Matheron and Porchas (http://cals.arizona.edu/pubs/crops/az1419/9_WEB.PDF).
Early detection and treatments are important since control is very difficult once disease develops. Varieties with tolerance to Podosphaera xanthii (Sphaerotheca fuliginea) are available.
Diseases of melon ( Cucumis melo ) in Arizona
Pythium root rot and seedling damping-off
Pythium root rot of melons in Arizona is usually caused by Pythium aphanidermatum, but other Pythium species may also be involved. Pythium species are soil borne organisms that are common in agricultural soils. Pythium aphanidermatum is active when soil temperatures are warm, above about 85 F, and very moist. Motile asexual spores called zoospores are produced in wet soils, and these spores can infect roots within a few hours. A thick-walled sexual spore, produced in infected tissue, can remain inactive in the soil for months or years, germinating only when a susceptible host is present under suitable environmental conditions. Infected roots are brown then become soft and very dark. In seedlings, the roots are rotted quickly and young seedlings fall over or "damp-off" when infected.
Damping-off of seedlings can be reduced by planting into pre-irrigated soils that are still moist since under these circumstances the soil is cooler and the seedling begins to grow faster, both of which reduce chances of infection. Metalaxyl fungicide is effective for controlling Pythium aphanidermatum and can be applied as a soil drench or through drip lines. It is important to get a confirmed diagnosis before application of metalaxyl since there have been reports of resistance with repeated applications. There are no tolerant melon varieties.
Diseases of melon ( Cucumis melo ) in Arizona
Reported viruses
Several viruses have historically been severe problems of melons in Arizona although their incidence and severity fluctuate. These are listed with their host range, symptoms, vector and available control strategies:
Papaya ringspot virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 1) infects cucurbits only. It causes mottled and mosaic leaves, blisters and distortion. It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties.
Watermelon mosaic virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 2) infects cucurbits, many weed species and especially legumes; it causes variable symptoms including mottled and mosaic leaves and stunting (photos 1 and 2). It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties. It occurs throughout Arizona wherever cucurbits are grown.
1 2
Zucchini yellows mosaic virus (Potyviridae, Potyvirus, ssRNA) infects cucurbits but little is known of other off-season hosts. It causes severe mosaic, shoe-stringing, stunting, and blisters (photo 1). It is sap transmissible and is carried non-persistently by aphids; it is not seed borne. There is tolerance in some varieties.
1
Lettuce infectious yellows virus (Closteroviridae, Crinivirus, ssRNA) infects cucurbits and many other hosts; it has been uncommon in Arizona for the past several years. It causes leaf yellowing, usually on older leaves and stunting (photos 1 and 2). It is carried semi-persistently by the sweet potato whitefly, Bemesia tabaci biotype 1 and has disappeared as biotype B, not a vector, has become dominant. It is not seed borne. Sanitation and weed control may reduce incidence.
1 2
Beet curly top virus (Geminiviridae, Curtovirus, ssDNA) infects cucurbits and many other hosts; it causes leaf cupping and rolling, plant dwarfing and chlorosis. It is transmitted by the beet leafhopper, Circulifer tenellus. It is rarely problematic in melons in Arizona. There are no tolerant varieties, and no control measures are practiced.
Squash mosaic virus (Comoviridae, Comovirus, ssRNA) infects cucurbits only; it causes a mild mosaic to a severe leaf mottle, yellowing and stunting (photo 1). Squash mosaic virus is seed borne, sap transmissible and carried persistently by cucumber beetles. The best prevention is the use of clean seed.
1
Cucumber mosaic virus (Bromoviridae, Cucumovirus, ssRNA) infects cucurbits and many other hosts; it causes mild to severe leaf mosaic, stunting and deformed fruit. It is sap transmissible, is carried non-persistently in many species of aphids. It may be seed borne in other hosts but reportedly is not seed borne in cucurbits. In Arizona, it is often more of a problem on peppers than on cucurbits.
Cucurbit yellow stunt disorder virus (CYSDV) (Closteroviridae, Crinivirus, ssRNA) is a whitefly transmitted virus that was first observed in southwestern Arizona in fall 2006. Although the virus has been observed in Texas in the lower Rio Grande Valley and the Presidio area of West Texas since 1999 as well as in Sonora, Mexico, it was not detected in the Southwestern deserts until fall 2006. In fall 2007, it was widespread throughout all the melon growing areas in Arizona. The virus is most severe in cantaloupe in which it causes yellowing of leaves over much of the plant and low fruit sugar.
A diagnostic feature in melon leaves is the presence of green dots within the yellowing leaf (photo 1). Watermelon is susceptible, but is not as severely affected as cantaloupe. Preventive measures for cantaloupe may include whitefly control and the eradication of volunteer cucurbits in nearby areas such as citrus orchards and backyard gardens. However, the origin of the rapid widespread infections in southwestern Arizona in fall 2006 is unknown, and local control measures may be of little help if they were the result of sudden infestations of whiteflies carrying the virus from other areas as a result of active summer "monsoon" rainstorms.
1
For more information, see the following web sites: http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Cucurbit/CucViruses/CucVirPhotoList.htm http://www.ipm.ucdavis.edu/PMG/r116300611.html http://www.ipm.ucdavis.edu/PMG/r116101811.html
Diseases of melon | Plant Disease Identification | Extension Plant Pathology
February 20, 2013
http://cals.arizona.edu/PLP/plpext/diseases/vegetables/melon/melonvir.htm
Diseases of melon ( Cucumis melo ) in Arizona
Reported viruses
Several viruses have historically been severe problems of melons in Arizona although their incidence and severity fluctuate.
These are listed with their host range, symptoms, vector and available control strategies:
Papaya ringspot virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 1) infects cucurbits only. It causes mottled and mosaic leaves, blisters and distortion. It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties.
Watermelon mosaic virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 2) infects cucurbits, many weed species and especially legumes; it causes variable symptoms including mottled and mosaic leaves and stunting (photos 1 and 2). It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties. It occurs throughout Arizona wherever cucurbits are grown.
1 2
Zucchini yellows mosaic virus (Potyviridae, Potyvirus, ssRNA) infects cucurbits but little is known of other off-season hosts. It causes severe mosaic, shoe-stringing, stunting, and blisters (photo 1). It is sap transmissible and is carried non-persistently by aphids; it is not seed borne. There is tolerance in some
varieties.
1
Lettuce infectious yellows virus (Closteroviridae, Crinivirus, ssRNA) infects cucurbits and many other hosts; it has been uncommon in Arizona for the past several years. It causes leaf yellowing, usually on older leaves and stunting (photos 1 and 2). It is carried semi-persistently by the sweet potato whitefly, Bemesia tabaci biotype 1 and has disappeared as biotype B, not a vector, has become dominant. It is not seed borne. Sanitation and weed control may reduce incidence.
1 2
Beet curly top virus (Geminiviridae, Curtovirus, ssDNA) infects cucurbits and many other hosts; it causes leaf cupping and rolling, plant dwarfing and chlorosis. It is transmitted by the beet leafhopper, Circulifer tenellus. It is rarely problematic in melons in Arizona. There are no tolerant varieties, and no control measures are practiced.
Squash mosaic virus (Comoviridae, Comovirus, ssRNA) infects cucurbits only; it causes a mild mosaic to a severe leaf mottle, yellowing and stunting (photo 1). Squash mosaic virus is seed borne, sap transmissible and carried persistently by cucumber beetles. The best prevention is the use of clean seed.
1
Cucumber mosaic virus (Bromoviridae, Cucumovirus, ssRNA) infects cucurbits and many other hosts; it causes mild to severe leaf mosaic, stunting and deformed fruit. It is sap transmissible, is carried non-persistently in many species of aphids. It may be seed borne in other hosts but reportedly is not seed borne in cucurbits. In Arizona, it is often more of a problem on peppers than on cucurbits.
Cucurbit yellow stunt disorder virus (CYSDV) (Closteroviridae, Crinivirus, ssRNA) is a whitefly transmitted virus that was first observed in southwestern Arizona in fall 2006. Although the virus has been observed in Texas in the lower Rio Grande Valley and the Presidio area of West Texas since 1999 as well as in Sonora, Mexico, it was not detected in the Southwestern deserts until fall 2006. In fall 2007, it was widespread throughout all the melon growing areas in Arizona. The virus is most severe in cantaloupe in which it causes yellowing of leaves over much of the plant and low fruit sugar.
A diagnostic feature in melon leaves is the presence of green dots within the yellowing leaf (photo 1). Watermelon is susceptible, but is not as severely affected as cantaloupe. Preventive measures for cantaloupe may include whitefly control and the eradication of volunteer cucurbits in nearby areas such as citrus orchards and backyard gardens. However, the origin of the rapid widespread infections in southwestern Arizona in fall 2006 is unknown, and local control measures may be of little help if they were the result of sudden infestations of whiteflies carrying the virus from other areas as a result of active summer "monsoon" rainstorms.
1
For more information, see the following web sites: http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Cucurbit/CucViruses/CucVirPhotoList.htm http://www.ipm.ucdavis.edu/PMG/r116300611.html http://www.ipm.ucdavis.edu/PMG/r116101811.html
Diseases of melon | Plant Disease Identification | Extension Plant Pathology
February 20, 2013
http://cals.arizona.edu/PLP/plpext/diseases/vegetables/melon/melonvir.htm
Alternaria leaf spot
Alternaria leaf spot is caused by the fungus Alternaria. The fungus produces dark, multicelled spores on host tissue only when there is substantial moisture, usually during summer rains. The spores are easily carried in wind and splashing water and infect only the leaves. Brown necrotic spots appear on the leaves wherever spores germinate and infect leaf tissue (photo 1). Spots are small at first then may enlarge and coalesce to form circular lesions with visible concentric rings (photo 2).
Disease severity is dependent on varietal susceptibility and environmental conditions. Extended periods of moisture and warm temperatures favor disease development. It is rarely a problem …show more content…
in melons in the low desert in central or southwestern Arizona, but may be a sporadic problem in southeastern Arizona and in the Wenden-Aguila area.
Applications of fungicides, chlorothalonil or mancozeb, are preventive only, so fungicides should be applied regularly at the onset of summer rains to fields or plants in areas where disease is known to have occurred previously. 1 2
Charcoal rot
Charcoal rot is caused by a soil borne fungus, Macrophomina phaseolina. This fungus is common in Arizona soils, and causes disease in wide variety of plants. The fungus produces microsclerotia, small black structures that develop under the cortical tissue of roots or on the surface of stem lesions, that enable it to survive in the soil for many years in the absence of a host.
M. phaseolina has been associated with late season vine decline. It is most problematic in fall melons and is rare in spring melons harvested before mid June. In Arizona, it is often isolated from pink colored root lesions and from rotted roots. In drip irrigated systems, M. phaseolina also causes water-soaked lesions on the stems and crown (photo 1) that may have an gummy exudate in which case the disease looks very similar to gummy stem blight (photo 2). Vines with stem lesions have yellowing and death of leaves (photo 3). Fruit may also become infected, resulting in a firm, dark-colored decay.
There are no control measures currently recommended for charcoal rot. Cultural practices such as rotation, deep plowing and maintenance of soil moisture have not been effective. There has been little or no effective disease control using solarization or fumigation. Charcoal rot may be found in the same fields at the same time as Monosporascus vine decline, and control measures recommended for Monosporascus vine decline may also be beneficial in reducing charcoal rot (see Monosporascus vine decline).
1 2 3
iseases of melon ( Cucumis melo ) in Arizona
Downy mildew
Downy mildew of melons is caused by Pseudoperonospora cubensis. P. cubensis is a fungal-like organism that causes foliar necrosis and decline, and like other downy mildews, is an obligate parasite infecting only cucurbits. It does not affect the roots. Disease occurs on melons in the late summer and early fall during summer monsoon rains and in the late winter and early spring when there rain and heavy dew. With sufficient moisture in the foliage, disease progresses rapidly. P. cubensis produces spores that are carried by splashing water, wind and rain. Plants of all ages are susceptible.
Early infections cause yellow spots on leaves that coalesce, and the leaf turns brown. When humidity is very high, especially early in the morning, a white to light purple growth is visible on the underside of leaves, which consist of asexual spores. Older leaves are usually infected first. In areas where disease has been previously confirmed, it is important to watch for the initial symptoms and signs of disease so that fungicides can be applied as soon as possible. Protectant fungicides such as chlorothalonil and mancozeb should be applied in rotation with fungicides of other modes of action such as Gavel, Ranman, Previcur and Tanos. Repeat applications of fungicides may be necessary if conducive weather conditions persist. Alternating different chemicals is important to avoid development of resistance.
For more information, see the following web site: http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg13.htm http://www.ces.ncsu.edu/depts/hort/hil/hil-8.html
Diseases of melon ( Cucumis melo ) in Arizona
Monosporascus vine decline
Monosporascus vine decline is caused by the fungus Monosporascus cannonballus.
Plants may be infected when they are young, but symptoms usually do not appear until vines are mature and fruit are developing (photo 1). Foliage may have necrotic areas in the leaves and a progressive decline in the entire crown (photo 2). Tan lesions are often observed on roots, and, in the later stages of disease only, small black specks appear (photo 3). These specks are the sexual reproductive stage of the fungus that contain large black spores - thus the species name cannonballus (photo 4). These spores are commonly found in many different soils, and the fungus seems to be indigenous to certain semiarid …show more content…
soils.
There is no resistance in melons, but some varieties are much more susceptible than others. Caravelle and Desert Mark are among the most susceptible. The presence of spores in soils can be determined in laboratory assays, but to date there has been no direct correlation between the numbers of spores in soil samples and the incidence or prevalence of disease. Monosporascus vine decline becomes more problematic when melon crops follow one another without rotation. Disease may become so severe that planting melons that will mature in late summer and early fall is not economical.
Monosporascus vine decline can be reduced in drip-irrigated systems by more frequent applications of water when plants have a heavy fruit load. Soil fumigation with 1.3 dichloropropene (Telone II) and chloropicrin applied prior to planting and application of fludioxonil (Cannonball) or thiophanate methyl (Topsin-M) through buried drip irrigation beginning at plant emergence (see label instructions), may suppress disease. Lifting roots out of the ground immediately after the last harvest may reduce build up of inoculum (spores) in the soil.
1 2 3 4
Diseases of melon ( Cucumis melo ) in Arizona
Powdery mildew
Powdery mildew of melons is caused by Podosphaera xanthii (Sphaerotheca fuliginea). Disease is found anywhere cantaloupe, honeydew and other melons are grown in Arizona; it is favored by moderate to high humidity and low light intensity. A white powdery growth on the leaf surface starts out as small spots, often on the lower leaf surface, and gradually covers the entire leaf (photo 1). The mycelium of the fungus grows over the leaf surface and produces many asexual spores that are easily carried in the wind (photo 2). These spores germinate on the leaf surface where new infections develop within a few days. Advanced infections cause necrotic areas in leaves that can become extensive and result in a severe decline in foliage. Photosynthetic area is reduced and fruit exposed to sun burning. Variability in pathogenicity has been demonstrated in the fungus, and several races have been described based on host range. Podosphaera xanthii ( Sphaerotheca fuliginea) has two mating types which is probably why the sexual spores of the fungus are rarely found.
Registered fungicides used for control include sulfur dust and micronized sulfur; strobulurin fungicides azoxystrobin (Quadris), pyraclostrobin (Cabrio) and trifloxystrobin (Flint); thiophanate-methyl (Topsin-M); chlorothalonil (Bravo); quinoxyfen (Quintec); triflumizole (Procure); and mancozeb. Disease incidence may be reduced when foliar applications of neem extract (Trilogy) or potassium bicarbonate products (Armicarb 100, Kaligreen) are applied. Fungicides with the same mode of action such as the strobilurins should not be used in rotation with each other. Results of effective rotations and fungicide efficacy are available from yearly field trials in Yuma by Matheron and Porchas (http://cals.arizona.edu/pubs/crops/az1419/9_WEB.PDF).
Early detection and treatments are important since control is very difficult once disease develops. Varieties with tolerance to Podosphaera xanthii (Sphaerotheca fuliginea) are available.
Diseases of melon ( Cucumis melo ) in Arizona
Pythium root rot and seedling damping-off
Pythium root rot of melons in Arizona is usually caused by Pythium aphanidermatum, but other Pythium species may also be involved. Pythium species are soil borne organisms that are common in agricultural soils. Pythium aphanidermatum is active when soil temperatures are warm, above about 85 F, and very moist. Motile asexual spores called zoospores are produced in wet soils, and these spores can infect roots within a few hours. A thick-walled sexual spore, produced in infected tissue, can remain inactive in the soil for months or years, germinating only when a susceptible host is present under suitable environmental conditions. Infected roots are brown then become soft and very dark. In seedlings, the roots are rotted quickly and young seedlings fall over or "damp-off" when infected.
Damping-off of seedlings can be reduced by planting into pre-irrigated soils that are still moist since under these circumstances the soil is cooler and the seedling begins to grow faster, both of which reduce chances of infection. Metalaxyl fungicide is effective for controlling Pythium aphanidermatum and can be applied as a soil drench or through drip lines. It is important to get a confirmed diagnosis before application of metalaxyl since there have been reports of resistance with repeated applications. There are no tolerant melon varieties.
Diseases of melon ( Cucumis melo ) in Arizona
Reported viruses
Several viruses have historically been severe problems of melons in Arizona although their incidence and severity fluctuate. These are listed with their host range, symptoms, vector and available control strategies:
Papaya ringspot virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 1) infects cucurbits only. It causes mottled and mosaic leaves, blisters and distortion. It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties.
Watermelon mosaic virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 2) infects cucurbits, many weed species and especially legumes; it causes variable symptoms including mottled and mosaic leaves and stunting (photos 1 and 2). It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties. It occurs throughout Arizona wherever cucurbits are grown.
1 2
Zucchini yellows mosaic virus (Potyviridae, Potyvirus, ssRNA) infects cucurbits but little is known of other off-season hosts. It causes severe mosaic, shoe-stringing, stunting, and blisters (photo 1). It is sap transmissible and is carried non-persistently by aphids; it is not seed borne. There is tolerance in some varieties.
1
Lettuce infectious yellows virus (Closteroviridae, Crinivirus, ssRNA) infects cucurbits and many other hosts; it has been uncommon in Arizona for the past several years. It causes leaf yellowing, usually on older leaves and stunting (photos 1 and 2). It is carried semi-persistently by the sweet potato whitefly, Bemesia tabaci biotype 1 and has disappeared as biotype B, not a vector, has become dominant. It is not seed borne. Sanitation and weed control may reduce incidence.
1 2
Beet curly top virus (Geminiviridae, Curtovirus, ssDNA) infects cucurbits and many other hosts; it causes leaf cupping and rolling, plant dwarfing and chlorosis. It is transmitted by the beet leafhopper, Circulifer tenellus. It is rarely problematic in melons in Arizona. There are no tolerant varieties, and no control measures are practiced.
Squash mosaic virus (Comoviridae, Comovirus, ssRNA) infects cucurbits only; it causes a mild mosaic to a severe leaf mottle, yellowing and stunting (photo 1). Squash mosaic virus is seed borne, sap transmissible and carried persistently by cucumber beetles. The best prevention is the use of clean seed.
1
Cucumber mosaic virus (Bromoviridae, Cucumovirus, ssRNA) infects cucurbits and many other hosts; it causes mild to severe leaf mosaic, stunting and deformed fruit. It is sap transmissible, is carried non-persistently in many species of aphids. It may be seed borne in other hosts but reportedly is not seed borne in cucurbits. In Arizona, it is often more of a problem on peppers than on cucurbits.
Cucurbit yellow stunt disorder virus (CYSDV) (Closteroviridae, Crinivirus, ssRNA) is a whitefly transmitted virus that was first observed in southwestern Arizona in fall 2006. Although the virus has been observed in Texas in the lower Rio Grande Valley and the Presidio area of West Texas since 1999 as well as in Sonora, Mexico, it was not detected in the Southwestern deserts until fall 2006. In fall 2007, it was widespread throughout all the melon growing areas in Arizona. The virus is most severe in cantaloupe in which it causes yellowing of leaves over much of the plant and low fruit sugar.
A diagnostic feature in melon leaves is the presence of green dots within the yellowing leaf (photo 1). Watermelon is susceptible, but is not as severely affected as cantaloupe. Preventive measures for cantaloupe may include whitefly control and the eradication of volunteer cucurbits in nearby areas such as citrus orchards and backyard gardens. However, the origin of the rapid widespread infections in southwestern Arizona in fall 2006 is unknown, and local control measures may be of little help if they were the result of sudden infestations of whiteflies carrying the virus from other areas as a result of active summer "monsoon" rainstorms.
1
For more information, see the following web sites: http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Cucurbit/CucViruses/CucVirPhotoList.htm http://www.ipm.ucdavis.edu/PMG/r116300611.html http://www.ipm.ucdavis.edu/PMG/r116101811.html
Diseases of melon | Plant Disease Identification | Extension Plant Pathology
February 20, 2013
http://cals.arizona.edu/PLP/plpext/diseases/vegetables/melon/melonvir.htm
Diseases of melon ( Cucumis melo ) in Arizona
Reported viruses
Several viruses have historically been severe problems of melons in Arizona although their incidence and severity fluctuate.
These are listed with their host range, symptoms, vector and available control strategies:
Papaya ringspot virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 1) infects cucurbits only. It causes mottled and mosaic leaves, blisters and distortion. It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties.
Watermelon mosaic virus (Potyviridae, Potyvirus, ssRNA) (Watermelon mosaic virus 2) infects cucurbits, many weed species and especially legumes; it causes variable symptoms including mottled and mosaic leaves and stunting (photos 1 and 2). It is sap transmissible and is carried non-persistently in aphids; it is not seed borne. There is tolerance in some varieties. It occurs throughout Arizona wherever cucurbits are grown.
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Zucchini yellows mosaic virus (Potyviridae, Potyvirus, ssRNA) infects cucurbits but little is known of other off-season hosts. It causes severe mosaic, shoe-stringing, stunting, and blisters (photo 1). It is sap transmissible and is carried non-persistently by aphids; it is not seed borne. There is tolerance in some
varieties.
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Lettuce infectious yellows virus (Closteroviridae, Crinivirus, ssRNA) infects cucurbits and many other hosts; it has been uncommon in Arizona for the past several years. It causes leaf yellowing, usually on older leaves and stunting (photos 1 and 2). It is carried semi-persistently by the sweet potato whitefly, Bemesia tabaci biotype 1 and has disappeared as biotype B, not a vector, has become dominant. It is not seed borne. Sanitation and weed control may reduce incidence.
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Beet curly top virus (Geminiviridae, Curtovirus, ssDNA) infects cucurbits and many other hosts; it causes leaf cupping and rolling, plant dwarfing and chlorosis. It is transmitted by the beet leafhopper, Circulifer tenellus. It is rarely problematic in melons in Arizona. There are no tolerant varieties, and no control measures are practiced.
Squash mosaic virus (Comoviridae, Comovirus, ssRNA) infects cucurbits only; it causes a mild mosaic to a severe leaf mottle, yellowing and stunting (photo 1). Squash mosaic virus is seed borne, sap transmissible and carried persistently by cucumber beetles. The best prevention is the use of clean seed.
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Cucumber mosaic virus (Bromoviridae, Cucumovirus, ssRNA) infects cucurbits and many other hosts; it causes mild to severe leaf mosaic, stunting and deformed fruit. It is sap transmissible, is carried non-persistently in many species of aphids. It may be seed borne in other hosts but reportedly is not seed borne in cucurbits. In Arizona, it is often more of a problem on peppers than on cucurbits.
Cucurbit yellow stunt disorder virus (CYSDV) (Closteroviridae, Crinivirus, ssRNA) is a whitefly transmitted virus that was first observed in southwestern Arizona in fall 2006. Although the virus has been observed in Texas in the lower Rio Grande Valley and the Presidio area of West Texas since 1999 as well as in Sonora, Mexico, it was not detected in the Southwestern deserts until fall 2006. In fall 2007, it was widespread throughout all the melon growing areas in Arizona. The virus is most severe in cantaloupe in which it causes yellowing of leaves over much of the plant and low fruit sugar.
A diagnostic feature in melon leaves is the presence of green dots within the yellowing leaf (photo 1). Watermelon is susceptible, but is not as severely affected as cantaloupe. Preventive measures for cantaloupe may include whitefly control and the eradication of volunteer cucurbits in nearby areas such as citrus orchards and backyard gardens. However, the origin of the rapid widespread infections in southwestern Arizona in fall 2006 is unknown, and local control measures may be of little help if they were the result of sudden infestations of whiteflies carrying the virus from other areas as a result of active summer "monsoon" rainstorms.
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For more information, see the following web sites: http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Cucurbit/CucViruses/CucVirPhotoList.htm http://www.ipm.ucdavis.edu/PMG/r116300611.html http://www.ipm.ucdavis.edu/PMG/r116101811.html
Diseases of melon | Plant Disease Identification | Extension Plant Pathology
February 20, 2013
http://cals.arizona.edu/PLP/plpext/diseases/vegetables/melon/melonvir.htm