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Cucumber mosaic virus (CMV) is a plant disease-causing virus that has a worldwide distribution and a very broad host range. It was named so for one of the first plants in which it was found, the cucumber.
CMV is found predominantly in temperate areas around the world. CMV cannot live in extremely dry conditions. The optimal temperature at which CMV expresses itself and shows symptoms appears to be between 79 and 89 deg. F.
The CMV is very minute and is made up of ribonucleic acid core which is surrounded by a protein coat. They have no mode of self-dispersal; hence rely on various vectors to transmit them from infected to healthy plants. Once the virus infects a plant cell, the protein coat dissolves and the nucleic acid portion takes over the cell’s nucleic acid and protein synthesis systems and directs them to produce more viruses, thus disrupting and affecting normal activity in the cell. CMV cannot survive for long outside a cell or if the cell dies and can multiply only inside a living plant cell.
CMV may be spread from infected plants to healthy plants in the following ways:
- Several aphid species serve as vectors for CMV
- Mechanically by humans and tools through cultivating and even touching healthy plants after touching infected plants
- Through grafting
- Can also be transmitted by seed
Vegetables and fruits such as cucumbers and other cucurbits, squash, melons, bananas, artichokes, peppers, beans, peas, potato, tomatoes, carrots, celery, lettuce, spinach, beets, various weeds and many ornamental and bedding plants such as lily, delphinium, primula and daphne.
Damage and Symptoms
The following symptoms are may be associated with CMV:
- Mosaic yellowish patches or green and yellow mottling on leaves
- Stunted growth due to shortening of the internodes (length between stem and leaves)
- Downward curling of leaves that are distorted and small in size
- Distinct yellowing of the veins only
- Ring-spots or line patterns on leaves or fruits
- Reduced yields and distorted fruit and flowers
- White streaks on flowers known as “breaks”
CMV shows symptoms on leaves known as the “Shoestring” effect for most host species. This phenomenon causes young leaves to appear narrow and the entire plant to be stunted.
Specifically CMV can cause cucumbers to turn pale and bumpy. The leaves turn mosaic and their rugosity is changed, making leaves wrinkled and misshapen. Plant growth is stunted, few flowers are produced, and fruits are oddly shaped and appear gray. Cucumbers like this are often referred to as “white pickles”. Infected cucumbers are often bitter.
In celery, CMV can cause streaking and spotting. In lettuce, infected plants show symptoms of chlorosis, stunting and often do not properly form heads.
Pepper plants often have severe foliar damage, noticed as mosaic and necrotic rings. The peppers are often misshapen and contain chlorotic rings and spots.
Tomato plants when infected by CMV are usually stunted and have poorly shaped leaves, or “fernleaf”.
The CMV overwinters in perennial weeds, flowers and often crop plants. In spring when plants bloom and grow the virus emerges in the top leaves where it may be transmitted to healthy plants by aphid vectors (although tomatoes are not the preferred host of aphids) or by mechanical means. CMV cannot withstand very dry conditions nor can it persist in the soil. It also is more difficult than tobacco mosaic to transmit mechanically. Thus, cucumber mosaic tends to progress more slowly than tobacco mosaic in a field or garden.
Organic Means of Control and Prevention of Cucumber Mosaic Virus
There aren’t any known substances that cure a plant of CMV, nor any that can protect it from getting infected. Hence control measures for plant viruses include prevention and eradication.
– When purchasing seeds and plants, ensure that they are virus-free.
– Strictly maintain and prevent aphids from infesting your plants. Here’s an Aphid control guide.
– Remove all weeds as they are likely sources of both CMV and aphids. Groundsel and chickweed are particularly likely to harbor CMV.
– Immediately set aside suspect plants and obtain a diagnosis. CMV infected plants must be destroyed.
– Apart from aphids, CMV can be transmitted through gardening tools and by contact with infected plants. Maintaining clean and sanitized tools, machines and hands can go a long way in preventing the transmission of CMV.
– Use resistant varieties whenever possible. Zucchini- ‘Supremo’, ‘Defender’. Bush marrow- ‘Badger Cross’, ‘Zebra Cross F’, ‘Tiger Cross’. Cucumbers- ‘Bush Champion’, ‘Crispy Salad’, ‘Jazzer F’, ‘Paskia Fi’, ‘Petita’, ‘Country Fair’. Aubergine- ‘Bonica’. These varieties have shown some resistance to CMV.
– Trap crop method: In this method farmers plant resistant varieties around the perimeter of their fields and place susceptible plants in the middle. The intention of this that aphids will first land on the resistant varieties and by the time they have eaten their way to the susceptible varieties they will no longer be carrying the virus.
– Avoid your tomato plants from getting infected by CMV by not planting tomatoes next to cucurbits, spinach, or other vegetables and flowers susceptible to these diseases.
Botrytis is a plant pathogenic fungus that is found virtually everywhere plants are grown and prefers damp, cool to mild weather. It grows quickly, can grow utilizing many different sources of nutrients, prevails easily in greenhouses, and attacks numerous plant types. The disease caused by Botrytis fungus is commonly called Botrytis blight or gray mold. There are several species of the fungus Botrytis which can cause blights; the most common is Botrytis cinerea.
Botrytis can infect many ornamental plants including: anemone, begonia, calendula, chrysanthemum, cyclamen, dahlia, dogwood, fuchsia, geranium, hawthorn, heather, hydrangea, marigold, pansy, periwinkle, peony, petunia, rose, snapdragon, sunflower, sweet pea, tulip, violet, zinnia.
Among vegetables and fruits Botrytis can infect asparagus, bean, beet, carrot, celery, chicory, crucifers, cucurbits, eggplant, endive, grape, lettuce, onion, pepper, potato, raspberry, rhubarb, rutabaga, shallot, strawberry, tomato, turnip, and others.
Initial contamination is usually through fungal spores carried about in the wind which infects host plant through a point of damage such as insect damage, decaying plant tissue or pruning wounds. Botrytis overwinters on plants, in or on the soil, and as sclerotia (compact mass of hardened fungus containing food reserves with the capability to remain dormant until favorable growth conditions return).
Spores develop when conditions are optimal, and are moved around by wind or splashing water onto blossoms or young leaves, where they germinate and enter the plant. Spores require cool temperatures (45-60 deg. F) and high humidity (93% and above) to germinate. Green, healthy tissue is rarely penetrated by germinating spores, but they can enter through wounds on growing plants. Cuttings are particularly prone to infection.
The soil surface and the densest areas of plant canopy are likely places for Botrytis to be found. It usually develops on wilted flowers first, and then quickly spreads to other parts of the plant. Harvested fruits and vegetables in storage are also potential targets of the disease.
Symptoms and Damage
On flowering plants, the first symptoms you may see will be water-soaked spots on the leaves, flowers, or stems. These spots will quickly develop fuzzy gray or whitish growth. Infections often start as flower blights because older petals are more susceptible. Damage will soon spread to other flowers and parts of the stem, which then collapse as the flowers dry and turn brown.
On fruiting plants, a gray, tan, or whitish fluffy mold grows on berries and other fruit, which when disturbed, will emit of a puff of gray spores that scatter. Infected fruit will have water-soaked spots, which later appear light brown and crack as the fungus grows. On berries the entire fruit becomes water-soaked and rots.
Organic Control and Prevention of Botrytis Blight
1. Practice good sanitation: Strict sanitation is of utmost importance and cannot be overemphasized. Remove dead or dying tissue from the plants and from the soil surface as the fungus readily attacks them and produces tremendous quantities of airborne spores. All old blossoms and dead leaves should be removed, and all fallen leaves and plant debris in the garden and greenhouse should be carefully collected and burned or hauled away with the trash. Ideally, all diseased plants and plant parts should be removed and destroyed. Botrytis spores are always present, but they don’t germinate until exposed to cool and moist conditions, especially high humidity. Try and prevent these conditions from being prevalent for long.
2. Avoid overhead watering: Water on foliage and flowers from overhead watering, especially on cool, cloudy days, promotes the disease. Try keeping the plant parts above the surface dry. Soil surface irrigation and watering in the morning is recommended.
3. Properly space plants for maximum air circulation: The fungus thrives in areas that are cool and moist and in densely packed areas. Prune or stake the interior of dense plants to increase air movement. In greenhouses, ensure maximum air circulation by either increasing heat in the greenhouse or inculcating forced circulation and ventilation. Even lowering the humidity slightly can have a significant effect on Botrytis.
4. Avoid over-fertilization: Do not over-feed your plants, especially with nitrogen as tender growth is susceptible to fungus.
5. Avoid unnecessarily wounding plants: Wounds are possible entry sites for pathogens of all types including Botrytis, so avoid injuring plants in any way. Do not leave large stubs of tissue on stock plants when taking cuttings.
6. Store harvest immediately in proper conditions: Only blemish-free, flowers, fruits, vegetables and plant material should be stored in clean, cool and dry environment without moisture on the walls, ceilings or floor. The temperature should be as close to freezing as possible.
7. Preventative biological fungicide: Developed from naturally occurring bacteria, Streptomyces griseoviridis, Mycostop biological fungicide thrives in the root zone of plants. When applied as a drench or spray the dried spores and mycelium of the Streptomyces culture in Mycostop germinate and begin to grow on and around the plant roots. In doing so, they create a biological defense against root infecting pathogenic fungi which cause disease such as wilt and root rot. This is a preventative treatment, and must be used at the time of seeding or transplanting. Mycostop has been shown to promote the growth and yield of plants even in healthy crops.
8. Plant resistant cultivars: Whenever possible grow plant varieties that are known to be less susceptible to Botrytis.
9. Organic fungicides: Spray susceptible plants with an organic fungicide like Neem oil or Soap-Shield to keep fungal diseases and other pests at bay.
Damping off or damping-off is a horticultural disease or condition, caused by a number of different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.
Damping off is caused by several soil-borne fungi including Pythium, Phytophthora, Rhizoctonia and Fusarium, which infect seedlings and cause them to “damp off” or collapse and decay.
Damping off can affect any seedling, particularly under high humidity levels, in cold wet soil, poor air circulation, poor soil drainage, use of green compost, and planting too deeply. Damping off is a huge problem when sowing seeds indoor early in the season or under glass, but can affect seedlings sown outdoors when specified conditions are prevalent.
Damage and Symptoms
Infected seeds don’t germinate; instead they turn mushy and brown. Seeds may be infected as soon as moisture penetrates the seed coat or a bit later as the radicle begins to extend, all of which rot immediately under the soil surface. This pre-emergence damping off results in a poor, uneven stand of seedlings, often confused with low seed viability.
When seedlings are attacked after they emerge, stem tissue near the soil line decays, weakens and gets a dark, water-soaked area, usually causing the plants to topple over and die. When only roots decay, the plant may continue standing but will remain stunted, wilted and will eventually die.
Older plants that are infected have stem lesions that cause stunted growth, and can die.
Seeds and seedlings of most plants.
Organic Control and Prevention of Damping off
– Cultural control of damping off diseases is based on providing favorable conditions for germination of the seeds and growth of plants while minimizing the conditions that favor fungi. This means growing seeds in well-drained soil, with adequate air circulation and dry conditions.
– Use sterile well drained soil mediums. Avoid wet or compacted soil. Raise seedlings in treated commercial growing compost. If home-produced compost is being used, steam-sterilize the compost to destroy pathogens. Soil mix has to be held at 140 deg. F for at least 30 minutes to ensure sterilization.
– Purchase disease free plants and seeds from a trusted supplier. Seed borne diseases can be avoided by soaking seeds for 15 minutes in bleach soak (1 teaspoon per quart of water) prior to sowing.
– In warm regions, practicing soil solarization can reduce pathogens in outdoor soil. To solarize, place clear plastic tarps over soil for extended periods.
– Use plant containers that have drainage holes, water from the bottom only and strictly avoid over-watering. Do not allow pots to stand in water as the excess water will starve the roots of oxygen.
– Ideally, use new pots and trays to raise seedlings. If re-using old ones, make sure to disinfect them thoroughly. Never reuse pots and trays in which damping off has been a previous issue.
– As a rule of thumb, do not cover seeds with soil mix more than 4 times the thickness of the seed. Do not allow for the crowns of plants to be below the soil line.
– Use only well-decomposed compost. Do not use the green compost as its overly moist environment will encourage damping off fungi. Use well aerated composting soil to reduce chances of infection. Composted hardwood bark has been reported to reduce damping off.
– Cover seedlings with a thin layer of perlite, vermiculite, sand, or peat moss to keep the soil surface dry and keep fungal growth to a minimum.
– Avoid overcrowding and overfeeding of seedlings. Maintaining constant levels of growth through proper lighting and adequate control of growth environment is important and helps prevent damping off.
– Avoid working with plants (cuttings or transplants) when the soil is wet.
– Disinfect tools, containers and hands after working in areas that are likely to harbor damping off fungi.
– Drench starting soil mix with an anti-fungal agent. Chamomile tea, clove tea and garlic infused water have anti-fungal activity.
– Use water that you know is free from pathogens. Your mains water will mostly be safe for use on seedlings grown in pots and trays. If using rainwater, ensure that the water butt is covered to prevent the entry of leaves and other organic debris that could harbor pathogens.
– Remove and discard diseased plants.
– Avoid planting the same crops in the same place year after year.
– Unfortunately infected seedlings usually die, but sometimes you can save the rest by improving growing conditions by making them as warm and dry as possible.
– Spray plants with seaweed extract as this will help strengthen them.
– Spray plants with Neem oil as it has anti-fungicidal properties as well as providing systemic benefits to the plant.
Keep your zucchini, crookneck and pattypans safe!
–The fruit develops a disease that is similar to tomato blossom end rot which happens when the water given to the plants is uneven which creates a calcium deficiency. This can be prevented by mulching to keep the soil moisture even, and by watering regularly to give the plants adequate water.
–The second reason is that the flowers themselves develop a fungus and rot back into the fruit. This happens especially in areas or gardens that have high humidity, or where gardens are watered from above and plants are kept wet for long periods of time.
In either case mentioned above, the answer to the problem is simple:
-Ensure even watering, adequate and be sure to not indulge in over-fertilization, maintain appropriate pH between 6-6.5 for better calcium uptake and add a calcium rich spray or supplement to the soil.
-Remove the flowers once the young fruit has begun to swell and grow. After you remove the flower, if you see any decay starting, using your fingernail gently scrape the end of the fruit to remove any decaying material. A small scar will form where you did this, but the rot will stop and your squash will develop into mature fruit with no further problems.
Blossom-end rot is a common physiological problem associated with growing conditions that can affect susceptible plants anywhere. It affects fruit. Stems and leaves show no symptoms.
Blossom-end rot is a non-infectious disease or disorder of fruits caused by low levels of calcium in the fruit. For example, a tomato’s fruit needs calcium to grow. Calcium acts like glue, binding cells together. Tomatoes absorb calcium through water but calcium isn’t fast moving. If a tomato grows rapidly, or if some other conditions slow water absorption, then calcium doesn’t circulate evenly throughout the fruit. The tomato’s tissues breakdown and leave the telltale damage of blossom-end rot on its bottom end.
Several factors can limit a plant’s ability to absorb enough calcium for proper development. These include:
- fluctuations in soil moisture (too wet or too dry)
- excess nitrogen in the soil (lowers calcium uptake)
- root damage
- cold temperatures/cold soil
- soil pH that’s markedly acidic or alkaline
- excessive heat
- soil high in salts (lowers the availability of calcium)
Plants Commonly Affected
Tomato, pepper, cucumber, squash, eggplant, watermelon and other fruiting vegetables.
Damage and Symptoms
Blossom-end rot occurs on both green and ripe fruits and is characterized by a water-soaked, sunken, or brown spot on the blossom end of the fruit when the fruits are approximately half their full size. The spot then enlarges and turns into a leathery brown or black patch. If the problem is severe, the fruit will have a flattened or somewhat concave bottom end. Blossom-end rot will not spread from plant to plant or from fruit to fruit. The plant will generally show no signs of damage, yet the fruit will show tell-tale signs of blossom-end rot.
Organic Control and Prevention of Blossom-End Rot
- Protect young seedlings from extreme temperatures and conditions by gradually hardening them off.
- Grow plants in soil with good drainage.
- Plant outside at the right time when soil is warm enough. Avoid setting plants out too early in the season, which can expose them to cold soil and temperatures.
- Soil worked with organic matter and compost will allow the plant’s root system to grow strong and deep.
- Avoid excessive nitrogen fertilization. Ensure adequate phosphorous levels.
- Test your soil pH; tomatoes grow best at a soil pH of about 6.5. If needed, add quick-release lime to provide plenty of absorbable calcium.
- Supply water evenly throughout the season to facilitate regular uptake of calcium. Tomatoes need 1-3 inches of water a week. They are known to prefer deep watering a couple of times a week rather than everyday superficial watering.
- Avoid close, deep cultivation after fruit set, especially in dry weather. Scraping the soil lightly with a hoe is usually sufficient to control weeds in home gardens.
- Mulch established plants to conserve moisture and provide a more uniform water supply. Suitable materials are straw free of weed seeds, corncobs, grass clippings, peat moss and newspaper.
- Cultivate carefully around plants to avoid damaging root systems.
- Choose resistant vegetable varieties whenever possible.
Blossom-end rot cannot be reversed on fruits once it’s set in, but steps can be taken to slow and halt it.
- At the first sign of blossom-end rot, pay attention to watering and mulching. Even out water supply to the plant so that it is never super dry and then super wet, instead make sure it has a steady, even supply of water.
- Preserve affected plants by applying calcium immediately. Spray plants with natural calcium solutions such as Enz-Rot and Rot-Stop, which are specifically meant to treat blossom-end rot by correcting calcium deficiency. Follow label directions for application. Or mix 1 tablespoon calcium chloride in 1 gallon of water. Apply in the morning when temperatures are cool.
- Reduce stress on the plant by picking affected fruit and thus allowing it to direct its energy to other tomatoes.
- Cut out rotted spots on harvested fruit as blossom-end rot does not make the rest of the tomato inedible. However, if tomatoes have been infected by fungi or mold, discard them.
- Spray with seaweed extract help supply some calcium to affected plants.
Most plants usually grow out of the problem later in the season when growing conditions have been corrected. Determinate varieties are more prone to blossom-end rot because they set fruit in a short period of time, whereas indeterminate and semi-determinate varieties set fruit throughout the season, allowing for easier calcium regulation for plants.