Squash mosaic virus (SMV) is a common disease affecting many types of squash including but not limited to: Butternut, Cucurbita, Galia, Honeycrisp, Kiwi, Lychee and Summer Squashes. It affects both wild and cultivated varieties of these fruits. SMV is caused by a single species of fungus called the Solanum molybdites (the blue mold). The spores are carried in the soil or water where they germinate when moisture is present. They grow rapidly and multiply until conditions become unfavorable enough for them to reproduce. When they do, they produce a large number of small round cells which look like tiny black dots on the surface of the fruit. These cells are then covered with a thin layer of white powdery material called mycelium.
The mycelium produces a network of tubes called hyphae which extend from the center of the cell outwards into the surrounding tissue. The hyphal strands form a protective covering over the cells and prevent them from drying out, rotting or other problems. If there is no mycelium protecting the cells, they will dry out and die.
If too much moisture accumulates around the cells, they may begin to rot before reaching maturity.
Why Is This Important?
The disease is spread by contaminated tools, clothing, hands or other items that have the infection on them. Once the fungus has infected a plant, it can remain there for an extended period of time until the next time conditions are right for it to reproduce. The fungus can then spread rapidly throughout the plant if the conditions are right.
How Do I Recognize The Disease?
Although there are no visual signs that a plant is infected with this disease, it may show the following symptoms:
Affected leaves become light or dark green and may have a mottled pattern. They also appear to be streaked or webbed between major veins. Small yellow growths called spines may form along the edges of leaf blades giving them a furry appearance.
The fruit shows similar symptoms including mottling and striping between the ribs. They may also develop a lighter green color. In addition, the fruit may become misshapen or display a knobby appearance.
The skin may become thicker than normal or develop a warty look.
The inside of infected fruit shows that the seeds have turned dark and may be covered in small black dots. These dots are the fruiting bodies of the fungus. The flesh of the fruit displays striations similar to that of the leaves and becomes increasingly soft and mushy as it ripens.
How Do I Control It?
Controlling this disease is fairly easy. Since it is caused by a fungus, controlling it involves several strategies that debilitate the fungal cells. These include: Siting plants in well-drained areas that are not continually wet. Avoid planting where other affected plants have grown in previous years. Rotate crops. Sunlight helps to slow the spread of the fungus so avoid excessive shading of plants.
Inspect tools, boots and clothing to make sure they are free of fungal growth before entering the garden. If they are, disinfect them before use. This can be done by wiping them with a cloth or brushing them against a bar of soap.
If infected plants are found, remove and destroy them as soon as possible to prevent further spread. While you are performing this task, make sure that your tools, clothing and boots do not become contaminated.
Gardeners should avoid planting cucumbers next to barley, corn, oats, peanuts and tomatoes as these plants have been shown to be susceptible hosts for the fungus. It should also be noted that many plants such as carrots, beans, peas and radishes will gladly grow among cucumber crops without being infected so planting these can provide some protection for your cucumbers.
Insects and animals do not play a role in the spread of this disease so there is no need to worry about them.
How Can I Tell If My Cucumbers Are Infected?
Once the plant displays any of the visual symptoms described above, the fungus has started to spread throughout the plant. By this time it is too late for treatment as the damage has already been done.
How Can I Prevent The Spread Of This Disease?
As briefly mentioned above, the best way of preventing the spread of this disease is by cleaning your equipment and making sure it does not come into contact with any infected plants. However, if you grow cucumbers in a small enough space, such as in pots or containers, you can prevent its spread through insect and animal vectors.
What Insects Are Involved?
Most insects do not actually transmit the virus from one plant to another. It does however attract several types of insects that feed on the sticky honeydew produced by the sap-sucking insects. These include several species of ants, bees and other wasps. These insects help to spread the disease as they move from plant to plant feeding on the honeydew.
What Animals Are Involved?
Just like the insects, most animals do not actually transmit the virus. However birds do play a major role in its spread. Most species of birds do not feed on plant material, but will feast on the insects that are attracted to the honeydew that is excreted by the sap-sucking insects.
The birds do not contract the virus from feeding on the infected plants, however they then carry it to other plants as they feed. It has also been shown that in rare cases the virus can be transmitted through their droppings.
What Can I Do To Prevent The Spread?
As well as disinfecting your tools and equipment, you can prevent the spread of the disease through insect and animal vectors by covering your plants. This prevents the sap-sucking insects from feeding on your plants and in turn prevents the production of honeydew which in turn deters the birds from feeding on your plants.
How Does This Virus Affect My Cucumbers?
The symptoms that the virus produce in cucumbers are very apparent. The main visual feature is that of mottling with a purple hue on the outside of the plant near the veins. There will also be yellow or brown streaks running down the insides of the veins especially near the middle and bottom of the plants. The other major symptom is that of stunting whereby the plants themselves will be shorter than they should be.
The other major way in which cucumber mosaic virus affects your crop is by reducing the yield. The reason for this is that the infected plants themselves do not grow to their full potential, let alone have the energy to produce fruit.
What Should I Do If My Cucumbers Are Infected?
The best way to deal with this disease is to simply prevent it from spreading in the first place. As briefly mentioned above, this can easily be done by making sure that your tools and equipment are properly cleaned and covered. If however you do find that your plants are infected with the virus, there is little that can be done as far as treatment is concerned. The only option is to dispose of all the infected plants and stop any more spreading the virus onto other plants and into future generations.
Prevention Is Easier Than Cure!
If you take the time and trouble to clean and disinfect your tools and equipment before and after every harvest, you can vastly reduce, if not outright prevent the spread of this disease. There is little that can be done for an infected plant once the disease has taken hold, so prevention is always better than cure!
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Cucumber mosaic virus photos used courtesy of Prof. G.S.
Khush, Cornell University.
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Cucumber Mosaic Virus | How To Grow Cucumbers
Cucumber plants fall prey to a number of diseases and pests, all of which are more than willing to eat away at your delicious harvest should you let them. One of the most common and troublesome diseases that tends to affect cucumbers is Cucumber Mosaic Virus.
What Is Cucumber Mosaic Virus?
Cucumber mosaic virus (CMV) is a type of virus that is spread mainly by aphids, specifically the species of aphid called melon aphid which feed on a range of plants, most notably those in the Cucurbitaceae family, which includes both cucumbers and melons.
If you have a cucumber plant in your garden that is infected by this virus, you will usually notice a mottled green and yellow coloring on the leaves and stunted growth. The most telling sign of an infection is the appearance of tumors near the joints of the plant. These tumors are often identified by a buildup of white or yellow powders.
The virus is spread mainly by the aphids which feed on the sap of an infected plant and then go on to infect other cucumber plants. While the plant itself may survive the infection, it will most likely be greatly stunted and bear little fruit, if any at all.
How To Identify If Your Cucumber Plant Is Infected
As briefly mentioned above, you should look for signs of tumors appearing on your plant as an indication that it is infected. These tumors typically appear near the areas where the plant has joints, such as the stem connecting to the leaf or the place where a leaf is joined to the main stem.
The other sign that you should be aware of is a mottled coloring on the leaves of your plant. The leaves themselves will typically have yellow and dark green markings on them. These markings will typically be smaller than a penny and spread across the leaves.
You can also check your stem for signs of the virus by looking for small, bead like formations about the size of the tip of your little finger. These beads typically appear around the place where the stem is joined to either the leaf or the main part of the cucumber plant itself.
Sources & references used in this article:
Endophytic colonisation of squash by the fungal entomopathogen Beauveria bassiana (Ascomycota: Hypocreales) for managing Zucchini yellow mosaic virus in … by LR Jaber, NM Salem – Biocontrol science and technology, 2014 – Taylor & Francis
… -30 containing coat protein genes of cucumber mosaic virus, zucchini yellow mosaic virus, and watermelon mosaic virus-2 is resistant to these three viruses in the field by M Fuchs, JR McFerson, DM Tricoli, JR McMaster… – Molecular …, 1997 – Springer
Salicylic Acid-Induced Resistance to Cucumber mosaic virus in Squash and Arabidopsis thaliana: Contrasting Mechanisms of Induction and Antiviral Action by CN Mayers, KC Lee, CA Moore… – Molecular plant …, 2005 – Am Phytopath Society
Cross protection of cantaloupe with a mild strain of zucchini yellow mosaic virus: effectiveness and application by TM Perring, CA Farrar, MJ Blua, HL Wang… – Crop Protection, 1995 – Elsevier
Transmission and distribution of squash mosaic virus in seeds of cantaloupe by M Alvarez, RN Campbell – Phytopathology, 1978 – apsnet.org
Vegetable diseases: A colour handbook by ST Koike, P Gladders, A Paulus – 2006 – books.google.com
In vitro association between the helper component–proteinase of zucchini yellow mosaic virus and cuticle proteins of Myzus persicae by A Dombrovsky, N Gollop, S Chen… – Journal of General …, 2007 – microbiologyresearch.org
Interrelationships among inbreeding, herbivory, and disease on reproduction in a wild gourd by AG Stephenson, B Leyshon, SE Travers, CN Hayes… – Ecology, 2004 – Wiley Online Library
Transmission Efficiency of Cucumber green mottle mosaic virus via Seeds, Soil, Pruning and Irrigation Water by JX Li, SS Liu, QS Gu – Journal of Phytopathology, 2016 – Wiley Online Library