By: Bonnie L. Grant, Certified Urban Agriculturist
Ringspot virus of spinach affects the appearance and palatability of the leaves. It is a common disease among many other plants in at least 30 different families. Tobacco ringspot on spinach rarely causes plants to die, but the foliage is diminished, faded and reduced. Learn the signs and some preventions for this disease.
Spinach with tobacco ringspot virus is a disease of minor concern. This is because it is not very common and does not affect an entire crop as a rule. Tobacco ringspot is a very serious disease in soybean production, however, causing bud blight and failure to produce pods. The disease does not spread from plant to plant and is, therefore, not considered an infectious issue. That being said, when it does occur, the edible part of the plant is usually unusable.
Young or mature plants can develop ringspot virus of spinach. The youngest foliage shows the first signs with necrotic yellow spots evident. As the disease progresses, these will enlarge to form wider yellow patches. Leaves may be dwarfed and roll inward. The edges of the leaves will turn bronze in color. The petioles will also discolor and sometimes deform.
Severely affected plants wilt and are stunted. The disease is systemic and moves from the roots to the leaves. There is no cure for the disease, so prevention is the first path to control.
The disease infects plants through nematodes and infected seed. Seed transmission is probably the most important factor. Luckily, plants that are infected early rarely produce much seed. However, those that acquire the disease later in the season can bloom and set seed.
Nematodes are another cause of spinach with tobacco ringspot virus. The dagger nematode introduces the pathogen through the plant’s roots.
It is also possible to spread the disease through certain insect group’s activities. Among these include grasshoppers, thrips and the tobacco flea beetle may be responsible for introducing tobacco ringspot on spinach.
Purchase certified seed where possible. Do not harvest and save seed from infected beds. If the issue has occurred before, treat the field or bed with nematicide at least one month prior to planting.
There are no sprays or systemic formulas to cure the disease. Plants should be removed and destroyed. Most studies on the disease have been done on soybean crops, of which a few strains are resistant. There are no resistant varieties of spinach to date.
Using disease free seed and ensuring the dagger nematode is not in soil are the primary methods of control and prevention.
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Virus Diseases of Cucurbits
Fact Sheet Page: 732.40 Date: 10-1984
COOPERATIVE EXTENSION NEW YORK STATE CORNELL UNIVERSITY
by T. A. Zitter and M. T. Banik, Dept. of Plant Pathology, Cornell University, and R. Provvidenti, Dept. of Plant Pathology, New York State Agricultural Experiment Station, Geneva
Viruses are one of the most common causes of diseases affecting cucurbits in New York. These diseases result in losses through reduction in growth and yield and are responsible for distortion and mottling of fruit, making the product unmarketable. A complex of viruses is able to infect cucurbits. a plant group that includes cucumber, melon, squash, pumpkins, and watermelon. The most important viruses are cucumber mosaic (CMV), squash mosaic (SqMV), watermelon mosaic I (WMV-1), watermelon mosaic 2 (WMV-2), and zucchini yellow mosaic (ZYMV). With the exception of SqMV, which is seedborne in melon and transmitted by beetles, the other major viruses are transmitted by several aphid species in a nonpersistent manner.
Major Cucurbit Viruses
Squash mosaic virus (SqMV) can cause an important disease of melons and squash in New York. The virus is seedborne in muskmelon and is spread in nature principally by the spotted and striped cucumber beetles. The virus is carried within the seed and cannot be eliminated by hot water or chemical treatment with tusodium phosphate.
Symptoms consist of pronounced chlorotic mottle, green veinbanding, and distortion of leaves of young seedlings. On mature plants, leaves show intense dark green mosaic, blistering, and hardening, suggestive of a hormonal herbicide effect (fig. 1). Infected fruit coming from such plants show a strong mottled pattern with a lack of netting on melons (fig. 2). Control measures include selection of disease-free seed and cucumber beetle control.
Cucumber mosaic virus(CMV) is probably the most widely distributed and important virus disease of cucurbits in New York. The virus overwinters in many perennial weed sources especially attractive to aphids when weed growth resumes in the spring. Early infection of squash and melons is particularly common. Aphids are the main and most efficient method of virus spread. Summer squash displays severe downward cupping along the midvein and leaf reduction from which the plants fail to recover (fig. 3). Color breaking of squash fruit is usually seen, but is not unique for this virus other viruses causing this symptom include watermelon mosaic viruses 1 and 2, squash mosaic virus, and zucchini yellow mosaic virus. Early decline of muskmelon vines is usually attributed to CMV infection and should not be confused with collapse or "sudden wilt," which is a more complex disease and a plant-stress-related syndrome. CMV may be seedborne to a limited extent in some crops and weeds such as common chickweed (Stellaria media). Good CMV-resistant (actually tolerant since plants are infected by the virus) cucumber varieties are commercially available and produce a high percentage of unmottled fruit. All other commercially grown cucurbits are susceptible to CMV, although in yellow summer squash varieties that also carry a "precocious yellow gene," this gene serves to mask the color breaking common with cucurbit viruses (see discussion under WMV-2).
Watermelon mosaic virus 2(WMV-2) is the second most important cucurbit virus in New York. This virus can infect and produce symptoms on all commercially grown cucurbits. This aphid-transmitted virus causes milder symptoms on the foliage of most infected plants like squash (fig. 4), and growers have seen a lessening of foliar symptoms following fertilization. Fruit distortion and color breaking are still a problem on varieties like yellow straight-neck squash (fig. 5). Use of varieties such as 'Multipik' (fig. 6) can prolong the harvest period because the fruit are marketable in spite of foliar symptoms. The host range for WMV-2 is not limited to cucurbits, thus opening the possible overwintering of this virus in several leguminous species such as clover. Mixed infections of cucurbits with CMV and WMV-2 are common by the end of the season.
Watermelon mosaic virus 1 (WMV-1) is aphid transmitted, and infection is limited to cucurbits. Although more common in the southern and western regions of the United States, this virus has been recovered in New York several times since it first occurred in epidemic proportions in 1969. This virus is capable of infecting all commercial cucurbit crops. The foliage of affected plants shows strong mosaic, distortion, and deep leaf serration (fig. 7). Fruits are also malformed with knobby overgrowth (fig. 8).
Zucchini yellow mosaic virus(ZYMV) is a recently described virus disease of cucurbits, first identified in Europe in 1981. It has since been reported from most southern and southwestern states and was found in New York State in 1983. The virus has characteristics very similar to WMV-1 and WMV-2 (nonpersistent aphid transmission, etc.), and like WMV-2, its host range is not limited to cucurbits. Currently, none of the genetic factors that confer resistance to WMV-1 or WMV-2 are able to control ZYMV, but other resistance sources have been identified. Muskmelon, watermelon, and squash are severely affected by ZYMV. Foliar symptoms consist of a prominent yellow mosaic, necrosis, distortion, and stunting. Fruits remain small, greatly malformed, and green mottled, including fruit of the variety 'Multipik' (fig. 9). It is too early to tell which weed hosts may serve to overwinter this virus in New York.
Minor Cucurbit Viruses or Disease Agents
Tobacco ringspot virus (TRSV) is mainly transmitted by nematodes (Xiphinema americanun). Melons and cucumbers are most commonly affected by this virus. The virus has been known on rare occasions to be seedborne in cucurbits. The newly infected leaves show a very bright mosaic with plant stunting (fig. 10). but subsequent leaves are reduced in size and develop a dark green color.
Tomato ringspot virus (TmRSV) causes severe damage to summer and winter squash, but shows only mild symptoms in the other cultivated cucurbits. Like TRSV, TmRSV is nematode transmitted and can be overwintered on many weed species without expressing symptoms.
Clover yellow vein virus (CYVV) is an aphid- transmitted virus that can infect summer squash and was previously considered to be the severe strain of bean yellow mosaic virus. The virus produces a yellow specking on the foliage of infected plants.
Aster yellow mycoplasma(AY), formerly thought to be caused by a virus, has been recovered from infected squash in the state. This leafhopper-transmitted disease organism causes plants to become yellowed and stunted (fig. 11).
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White Rust (fungus – Albugo occidentalis): White rust is the major disease of spinach in Texas. White, blister-like pustules form on the lower side of the leaf. In advanced stages, the white lesions form on the upper side of the leaf. Generally, the upper surface will only be chlorotic. Plants infected with the white rust fungus are weak and collapse quickly if environmental conditions are favorable for disease development. Initial outbreaks each season follow source event such as hard rains that deposit soil and oospores on the young plants. The fungus oversummers in soil as dormant thick-walled oospores and may spread within a field by windblown spores. Free moisture on the leaf surface must be present for spore germination and development. The optimum temperature for germination is 54oF. The disease develops most rapidly at 72oF or during periods of cool, humid nights and mild day temperatures. No variety is totally resistant to white rust but a few have very useful partial resistance, including Green Valley II, Ozarka II, Coho and Fall Green. A disease control program should combine the benefits of cultural practices, partial resistance, a systemic fungicide at planting (in Texas, Ridomil 5G) and protective fungicides sprays (beginning 40-50 days after planting). Cultural practices should include long rotations, planting on beds and furrow irrigation. The risk of developing tolerance to Ridomil fungicide is reduced if all of these disease control practices are used together.
Downy Mildew or Blue Mold (fungus – Peronospora effusa): The downy mildew fungus first causes yellowish areas on the upper side of the leaf. The underneath side of the leaf is marked by a gray to violet-gray fungal growth mat that bears sporangia. The entire leaf is killed on susceptible varieties under optimum environmental conditions. The fungus overwinters in living spinach plants and in the seed. The fungus spores require surface moisture for development. Optimum temperature is around 48oF for germination and 54oF to 60oF for development. This disease can be controlled by the use of varieties resistant to races 1, 2 and 3.
Anthracnose (fungus – Colletotrichum spinaciae): Anthracnose shows up as small, dark olive colored spots. As the spots enlarge, they become tan in color. As the lesions coalesce, they kill the entire leaf. During periods of favorable disease development, the foliage appears as if the crop will be lost. With a change in weather, the diseased foliage drops off and the healthy foliage goes on to produce a crop. The fungus overwinters in seed and in crop refuse. Fungicides used in a white rust control will also control anthracnose.
Leaf Spots (fungi – Cercospora beticola, Heterosporium variable): These are minor diseases of spinach which may cause damage in some years. Cercospora leaf spots are white and, usually, small in size. Extended periods of precipitation and high humidity may allow spots to become large and even coalesce. Protective type fungicides offer some control. Ridomil does not control Cercospora.
Heterosporium leaf spots are larger and have a greenish black fungal growth on both sides of the leaf as the disease develops. Control measures are not generally recommended.
Fusarium Decline (fungus – Fusarium oxysporum f. sp. spinaciae): Plants are subject to infection at any stage of development. Infected plants turn yellow and wilt. The lower, older foliage is affected first. Plants which are infected are either stunted or killed. Infected plants lose their feeder roots and the vascular system of the taproot is darkened. The fungus is seed borne and can live in the soil indefinitely. Fortunately, white rust resistant varieties also have Fusarium resistance.
Blight (virus): Cucumber mosaic virus attacks spinach causing plants to become faintly chlorotic. Chlorosis increases until the entire plant becomes yellow. Crown leaves are narrow, wrinkled and develop an inward rolling of the margins. Plants are stunted. Death may occur in some severely infected plants. The virus is aphid transmitted. Most commercial varieties are resistant [see table].
Reaction of Spinach Varieties to White Rust and Blue Mold
|Variety||White Rust Reaction*||Blue Mold Race 3 Reaction*||Plant Type|
|Green Valley II||MR||S||semi- to full-savoy|
|Ozarka II||MR||S||semi- to full-savoy|
|Chinook II||S||R||semi- to full-savoy|
R = Resistant MR = Moderately Resistant MS = Moderately Susceptible S = Susceptible
Seedling Disease (fungi – Fusarium spp., Rhizoctonia spp., Pythium spp., Others): Preemergence and postemergence damping off can seriously reduce stands. Rotate with corn, plant after soils have cooled down in the late summer or fall, use a fungicide seed treatment and buy fresh, high quality seed.
Tobacco Ringspot (virus): First symptoms are small, indistinct, chlorotic spots which appear on the young foliage. These may coalesce to form large yellow areas. In advanced stages, leaves take on a copper bronze chlorosis. There is no malformation of the foliage. Affected plants rarely die but remain yellow and stunted. No control measures are known.
Beet Curly-Top (virus): Infected plants are marked by a rosette of tightly curled, small leaves in the center of the plant. As the disease develops, the growing point is killed and the plant dies. The virus is transmitted by beet leafhoppers.
Aster Yellows (mycoplasma-like organism): See Page on Aster Yellows.
False Root Knot (nematode – Naccobbus crucifera): Plants are stunted in cases of severe early infection, death will occur. The root system of infected plants is characterized by large galls covered with numerous rootlets. This nematode is particularly damaging on spinach plants in the fall. This nematode does little damage in hot soils.
Root Knot (nematode – Meloidogyne sp.): See Page on Root Knot.
Stress (abiotic – heat and/or saturated soils): The quality of spinach can decrease quickly following stress. Yellowing occurs within a few days after high temperatures and/or flooding. Choose planting dates carefully for your areas and provide good drainage.
Fact Sheet Page: 736.00 Date: 10-1984
COOPERATIVE EXTENSION NEW YORK STATE CORNELL UNIVERSITY
by T. A. Zitter and D. Florini Dept. of Plant Pathology Cornell University and R. Provvidenti Dept. of Plant Pathology New York State Agricultural Experiment Station, Geneva
Major Pepper Virus
Cucumber mosaic virus (CMV) is one of the most important virus diseases of pepper worldwide. The virus exists as a number of strains, but all are apparently capable of infecting pepper and differ only in symptom expression. The age of a plant at the time of infection strongly influences what types of symptoms will be manifested. CMV symptoms can be transitory and often appear on lower, mature leaves as ring-spot or oak-leaf necrotic patterns (fig. 1). Ring-spot symptoms are more prominent on determinate-type peppers. The necrotic symptoms, whether they occur on the foliage or on the fruit (fig. 2), are basically a shock reaction attributed to early virus infection. Sometimes plants adjacent to ring-spotted plants display only a mild to moderate mosaic pattern and have a general dull appearance (fig. 3). This difference may be influenced by the particular CMV strain involved, but more likely reflects the age at which plants are infected. With early infection, both quality and quantity of fruit produced will be affected.
CMV can infect more than 775 plant species including many weed species (chickweed, milkweed, purslane, etc.). CMV is spread by many aphid species in a nonpersistent manner, meaning that insecticides cannot prevent the spread of this disease. Strategies to delay early infection should be used to enhance yield and reduce the number of cull fruit. Isolate pepper plantings from weedy border areas or grow them next to taller border plantings, such as sweet corn, which can function as a nonsusceptible barrier crop. Mineral oil sprays have been used, primarily in the south in larger commercial pepper operations, to interfere with the transmission of all pepper viruses by aphids. No acceptable level of tolerance to CMV is available in any commercial variety.
Minor Pepper Viruses
Tobacco mosaic virus (TMV) is generally not a problem for pepper because most varieties are resistant to the common strains of the virus. Resistance is conferred by a single dominant gene, but two additional factors may be involved. Resistance operates by allowing infection to occur on inoculated leaves, which develop necrotic local lesions and abscise prematurely, thus preventing the virus from spreading systemically. Some strains of TMV, however, can systemically infect pepper and cause a mosaic on the foliage. Those strains are transmitted through seed, and the virus may also be mechanically spread by contact. Growers should be sure to start with healthy transplants.
Potato virus Y (PVY) is a common virus among solanaceous crops, infecting potato and tomato in addition to pepper. In southern states PVY ranks as one of the more important vegetable viruses. The symptom most useful for diagnosing PVY infection is a mosaic pattern that develops along the veins, commonly referred to as veinbanding (fig. 4). With early infection, plants are stunted, fruit set is reduced, and fruit express strong mosaic patterns making them unmarketable.
Like CMV, PVY is transmitted by several aphid species, but the green peach aphid is generally considered to be the most important vector. PVY has a limited host range, so elimination of solanaceous weeds bordering the crop would remove one potential source of inoculum. Because PVY is tuberborne in potato, isolation of peppers from potato plantings would be prudent. Other controls for PVY include choosing resistant varieties, which are presently limited, but should increase in number as more breeding is accomplished weed control and other methods outlined under CMV.
Tobacco etch virus (TEV) normally occurs along with PVY. However, sporadic occurrence of TEV alone has previously been noted in New York. Typical symptoms consist of broad dark-green mosaic bands along the veins, beginning at the leaf base and often continuing to the tip (fig. 5). The planting of PVY-resistant varieties generally helps control TEV because resistance to both viruses is closely linked however, there are a few strains of TEV that can infect PVY-resistant varieties. Other control measures have already been noted.
Pepper mottle virus (PeMV) bears many characteristics in common with PVY and TEV, including symptom expression. Veinbanding, as seen with PVY, is present, but the mottling is more extensive in interveinal areas and over the entire leaf surface (fig. 6). Fruit mosaic as noted in figure 7 is common for TEV, PVY, and PeMV. PeMV is limited to solanaceous spp., and control measures are those mentioned tor other pepper viruses.
Tomato spotted wilt virus (TSWV) can cause disease in a wide variety of plants including pepper, tomato, and lettuce. The virus is common in both temperate and subtropical areas of the world. Thrips transmit the virus, but only larvae, and not adults, can acquire the virus. Thus, only adults that fed on infected plants as larvae can transmit the virus and then only after a latent (incubation) period of 4 10 days. This type of transmission is much different from aphid transmission. The virus causes sudden yellowing and browning of the young leaves, which later become necrotic (fig. 8). Fruit formed after infection develop large necrotic blotches.
Use of insecticides to control the vector reduces disease incidence. Elimination of virus reservoirs (weed and ornamental species) near the crop is important but difficult to achieve.
Alfalfa mosaic virus (AMV), or "calico mosaic" as the disease is called when this virus infects potato, can occasionally be recovered from pepper. AMV is aphid transmitted in a nonpersistent manner and produces spectacular white or yellow calico symptoms on solanaceous crops, but milder symptoms on crop resevoirs like alfalfa and clovers. Infection probably causes little damage to pepper. Isolating peppers several feet from alfalfa and other legumes should diminish the chance for infection.
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Lots of line patterns with Tobacco Rattle Virus.
Cause Both Tobacco ringspot nepovirus and Tobacco rattle virus (TRV) have been reported on this host. TRV was confirmed on the OSU campus but it is unknown how extensively it occurs in the PNW. TRV is a rod-shaped virus with a positive sense ssRNA. Both viruses can be transmitted by nematodes.
Symptoms TRV - White line patterns or ringspots are found on many but not all leaves. White areas may cover 5% to 60% of a leaf. Pattern is different from leaf to leaf. Yellowing (chlorosis) or necrotic tissue does not seem to be a symptom. Plants are likely to be less vigorous and may not be as long-lived.