CUCUMBER - VIRUSES

BEET PSEUDO-YELLOWS VIRUS [BPYV]

Host range: Cucumber, muskmelon, squash, many ornamentals and other vegetable crops such as lettuce, endive, carrot, spinach and beet.
Occurrence and importance: Beet pseudo-yellows virus (BPYV) causes an important disease in greenhouse cucumber and muskmelon plantings.

1. Figure: Beet pseudo-yellows virus (BPYV) symptoms

Symptoms and confusable diseases: Symptoms first appear on older leaves as yellow interveinal chlorotic areas that may resemble nutritional deficiency. The yellow tissue becomes thickened and brittle as the disease progresses and eventually develops into necrotic lesions. Plant vigour is reduced, but fruit may not develop symptoms.

Transmission & Epidemiology: The greenhouse whitefly (Trialeurodes vaporariorum) transmits BPYV in a semi-persistently manner. BPYV is not mechanically transmitted. Symptoms begin to develop 2-4 weeks after infection. High light intensity is necessary for disease development.

Control:

Control of BPYV must focus on control of the greenhouse whitefly;
Weeds control;
The establishment of an ornamentals-free zone around the greenhouses is advised.
Implement a comprehensive insecticide program, crop rotation and a host-free period.

CUCURBIT YELLOW STUNTING DISORDER VIRUS [CYSDV]]

Host range: CYSDV causes a severe disease on cucurbit crops, especially on cucumbers and melons in the field, under glass, and in plastic greenhouses.

2. Figure: CYSDV symptoms

Occurrence and importance: CYSDV was first detected in Jordan (1991) and during the last decades has prevailed in the Mediterranean area due to the advantage its B. tabaci vector has given to its epidemiology as supposed to T. vaporariorum. CYSDV is common throughout many subtropical and tropical areas, including the European and Mediterranean region, the Middle East, North and Central America, and China. The economic losses from CYSDV are difficult to predict but are probably substantial.

3. Figure: CUCURBIT YELLOW STUNTING DISORDER VIRUS [CYSDV]

Symptoms and confusable diseases: Symptoms of infected plants show foliar mottling and interveinal chlorosis spreading outward along vines that are typical of damage caused by yellowing viruses. Moreover, symptoms may develop later to complete yellowing of the leaf lamina, except the veins, rolling and brittleness of the leaves and severe stunting on plants. Symptoms resemble Mg++ or Fe++ deficiencies.

Disease cycle: CYSDV is a crinivirus, semi-persistently transmitted by B. tabaci, silverleaf whitefly (further information /LINK/ here). The life cycle of CYSDV is strongly dependent on its vector, the whitefly B. tabaci. The spread of the virus may be related to the increase in the distribution of the polyphagous B. tabaci, which have a host range of around 600 host plant species. Within the European and Mediterranean region, B. tabaci has been reported from most countries.

The main pathways of CYSDV dispersal are through infected plants for planting and through adults, a vector, B. tabaci, associated with plant materials. As the virus is solely vector-transmitted, viruliferous adults of B. tabaci constitute the main pathway of local and natural dispersal.

Control:

Control of CYSDV is dependent on control of the tabaci;
Disease-free cucurbit seedlings;
Planting cucumber varieties with resistance/ tolerance to CYSDV;
Weed control;
Use of nets in greenhouses
Chemical control of tabaci is problematic because this pest develops resistance to most classes of insecticides.

ZUCCHINI YELLOW MOSAIC VIRUS

Host range: Host range of this virus is not yet well known. Some weeds (chickweed) can serve as overwintering hosts of the virus but the host range is not very broad, including mainly Cucurbitaceous species.

Occurrence and importance: This virus is very important in some regions of the Czech Republic, mainly in southern Moravia. The yield is severely affected and moreover fruits are malformed so that they are not marketable.

Symptoms and confusable diseases: Leaves of infected plants are yellow with severe mosaic and severe malformations. Fruits are distorted and malformed. Both growth and yield of infected plants are greatly reduced. First symptoms of mosaic could be confused with symptoms caused by CMV but ZYMV doesn´t cause leaf and fruit malformations.

4. Figure: ZUCCHINI YELLOW MOSAIC VIRUS

Transmission & Epidemiology: ZYMV is transmitted by several species of aphids (green peach aphid, cotton aphid etc.) in a non-persistent manner. The main source of infection at the beginning of the season is probably some overwintering weeds like chickweed. Possibility of seed transmission in squash still rests to be proved. Later on, the virus spreads inside of the crop from plant to plant. It is also seed transmissible.

Control:

No virtually effective method exists but some measures can be helpful in reducing the infection:

destroy any wild or self-sown cucurbit plants and weeds before planting – to reduce any potential virus and aphid sources for new crops;
remove any cucurbit plants showing virus symptoms, particularly before fruit set;
monitor surrounding weeds and crops for aphid populations;
plant a tall non-host (maize) border crop around the cucurbit crop about four weeks before planting – a non-host border acts as a cleansing barrier for aphids. Infective aphids that feed on it will lose the virus and will no longer be infective when they land on the cucurbit crop;
control aphid populations;
use certified virus-free seeds.

CUCUMBER MOSAIC VIRUS AND WATERMELON MOSAIC VIRUS

Host range: CMV has very broad host range including many weeds and ornamentals.

5. Figure: CMV distribution in Europe

Occurrence and importance: Both viruses are rather widespread in Europe and are important economically, especially CMV.

Symptoms and confusable diseases: Leaves of infected plants are mottled. In the case of WMV leaf malformations, stunting and rosetting of plants can also occur as well as misshapen and mottled fruits of reduced size. Both growth and yield of infected plants are reduced. Symptoms of WMV can be confused with those of ZYMV. Only specialized laboratory could discriminate both viruses.

Transmission and epidemiology: Both viruses are transmitted by aphids (green peach aphid, Myzus persicae; cotton aphid, Aphis gossypii, etc.) in nonpersistent manner. Various weed and perennial ornamentals serve as overwintering hosts and source of inoculum. Later on, the viruses are spread by aphids from plant to plant within the crop. CMV can be seed transmitted. For WMV some weeds can serve as overwintering hosts but the host range is not very broad.

Control:

avoid planting near perennial ornamentals,
elimination of aphids and weeds,
resistant varieties for CMV and WMV,
elimination of early infected plants,
mulch from glossy plastic foil repelents aphids but is usually too expensive,
barrier from taller nonhost plants (maize) around the crop,
application of mineral oils was proved to be effective against transmission of nonpersistent viruses, but it is rather expensive and the effect lasts several days only,
use certified virus-free seeds.

6. Figure CMV (on the left) and WMV (on the right)

Listo of Viruses:

WHITEFLY-TRANSMITTED VIRUSES
- BEET PSEUDO-YELLOWS VIRUS [BPYV]
- CUCURBIT YELLOW STUNTING DISORDER VIRUS [CYSDV]
ZUCCINI YELLOW MOSAIC VIRUS
CUCUMBER MOSAIC VIRUS AND WATERMELON MOSAIC VIRUS

For more information on viruses, follow this link.

Listo of bacterial:

ANGULAR LEAF SPOT

For more information on the bacterium, follow this link.

Listo of fungi:

DOWNY MILDEW
DAMPING OFF
POWDERY MILDEW
ANTHRACNOSE

For more information on fungi, follow this link.

List of disorders:

PHYSIOLOGICAL FLOWER FALL OFF
FLOWER DROP

For more information on disorders, follow this link.

List of insects:

APHIDS
THRIPS
WHITEFLIES
SPIDER MITES
SEED CORN MAGGOT

For more information on insects, follow this link.