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Posts Tagged ‘Fungus’

How to recognize plant disease

Wednesday, May 26th, 2010
Powdery mildew, a Biotrophic Fungus

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While the gardener hopes for disease-free plants, multitudes of organisms are ever present and merely biding their time for the appearance of the right conditions and host.

Damping-Off

Damping-off is likely the most discouraging problem for the gardener. Although it can occur any time during the growing season it generally attacks seedlings just when they seem to be getting off to a good start.

Damping-off is caused by fungi living right at the soil line where air meets the moist soil’s surface. If soil is kept continually damp the fungi attack the seedlings causing constricted stems at or immediately below the soil’s surface. The young plants fall over at the soil line and die.

Prevention is the only remedy. Allow the soil surface to dry out between waterings. If soil remains moist for a long period of time sprinkle the area around the seedlings with ground cinnamon. Cinnamon is a natural fungicide. The gardener may also make use of another natural fungicide, chamomile. Brew weak chamomile tea, let it cool and use around seedlings.

Mosaic Virus

Mosaic virus robs plants of their genetic organization, diverting energy to themselves. This virus primarily attacks summer and winter squash, gourds, cucumbers, watermelons and pumpkins although it also affects beans, peppers and tomatoes.

The virus causes abnormality in plant growth. Leaves look mottled or distorted and crinkled. They twist up or show bubbles. Often the affected plant will have leaves with yellowish spots on them. The fruit of affected cucumbers can have a variation of mottled light and dark green areas, sometimes paling almost white. Other fruit in the curcurbit family can be blanketed with warts or have skin that is faded, white and smooth. Although this virus may not kill the plant the fruit will taste so bitter that it will be inedible.

Mosaic virus overwinters in garden debris and a number of weed plants. Be sure the garden is scrupulously cleared out after the growing season and reduce or eliminate weed growth near food plants. Aphids and cucumber beetles also spread the virus when they feed from plant to plant. Eliminating these pests will go a long way toward preventing the virus from entering your garden.

Botrytis Blight

Botrytis blight or rot is a fungal disease that affects a number of vegetables and fruits. Among its host plants are asparagus, beans, beets, carrots, grapes, lettuce, onions, peppers, potatoes, raspberries, tomatoes and strawberries. The infection usually occurs when cool rainy or drizzling spring and summer weather lasts for several days. Botrytis rot can infect all parts of the plant except the roots. It appears as a mass of silver-gray spores on dead or dying plant tissue. Heavily infected plants release the spores as a dust that can be spread to other plants. The disease spreads most rapidly on wet or humid days and rain splatter also causes new infections.

As with other diseases, prevention is the best control. Inspect the plants often, watching for any infestation, blighted leaves or dead plants. Wait until the plants are dry before taking steps to sanitize them. Carry a paper bag with you when inspecting the plants. Remove infected plant material or the entire plant and place it in the bag to be thrown in the trash or burned.

Avoid overhead watering or misting which also provide favorable conditions for infection. Give plants plenty of space between them to promote good air circulation and allow the plants to dry out quickly, not giving botrytis the moist, humid conditions it needs in order to prosper.

Another fungal disease, powdery mildew, coats the leaves in dusty white or grey powder. Leaves are usually first attacked on the underside and then the mildew moves around to the top of the leaf, eventually covering the entire surface.

Sodium bicarbonate (baking soda) has proven to be extremely effective as an antifungal in treating active botrytis and powdery mildew. Add 1 ounce of baking soda to 1 gallon of water and spray the solution on the affected plant. Caught early, the disease can be halted and the plant saved.

Feeding all plants with finished compost or compost ‘tea’ foliar spray helps to strengthen their immune system, allowing the plants’ own defensive structures to ward off many debilitating diseases.

Vegetable & Garden Fungicide

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Common diseases in garden

Tuesday, May 4th, 2010
The human gut appears to harbor infectious str...
Image via Wikipedia

Plant diseases are caused by fungi, bacteria and viruses.
Most plant diseases are caused by fungal spores that tend to become a problem, especially during the wet weather season.

Fungi

Fungi are unable to generate nutrients on their own and in order to survive must derive their food from other organisms. Fungi attack all parts of a plant and under friendly conditions, fungi can damage plant translocation tissues; killing a plant in a quite short period of time. Some of the most common fungal diseases contain damping off, leaf spot, anthracnose and rust.

Bacteria
Plant diseases caused by bacteria are not as common as those caused by fungi. Damage caused by bacterial infection consequences primarily in rotting of the plant tissue.

Viruses
Viruses in plants are transmitted mainly often by sucking insects such as aphids and whiteflies. Viral diseases in general cause less damage than those vectored by fungi and bacteria. Infected plants typically become partly injured and weakened, however they infrequently die.

Plant diseases can spread without problems and rapidly. It is easier to fight and control fungal diseases than to eradicate bacteria and viruses. The best technique to prevent diseases is to take a proactive approach by preventing environmental factors that contribute to diseases combined with a healthy regimen that provides optimum health for plants.

In most cases, diseases can be prevented by using proper cultural practices such as variety selections, irrigation and humidity management, plant and soil nutrition, pruning, and row spacing. When there is insufficient circulation of air, poor water drainage, very expensive irrigation, and too much dampness due to rainfall, the fungi can become a problem.
The organic solution to these problems is to utilize copper and sulfur products. Spores are prevented from growing because the crop has been covered with the appropriate physical barrier.

It is essential to make the applications prior to rainfall to maximize success.
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White Mold of potato

Tuesday, April 27th, 2010

White mold of potato( also called sclerotinia stem rot) is caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary.

The disease well develop in moist conditions and is especially common in fields with overhead-irrigation such as by means of a center pivot. Agricultural practices that promote extensive canopy growth and keep relative humidity and free moisture in the crop canopy for extended periods of time and reduce wind movement, favor disease development.

Symptoms of white mold

White mold symptoms first appear as water soaked lesions 14 to 20 days following row closure. Lesions usually first appear in the intersections between the stem and branches, or on branches and stems in contact with the soil. These become quickly covered with a white cottony growth that can spread rapidly to nearby stems and leaves if moisture is present for several hours. As lesions expand they can girdle stems causing foliage to wilt. White mold is also often accompanied by bacterial stem rot, especially under wet conditions.

When conditions become dry, lesions dry out and turn beige, tan or bleached white in color and papery in appearance. As infected tissue decays, hard irregularly shaped resting structures called sclerotia form on the inside and outside of decaying tissue. No stem rot symptoms are observed on below-ground tissues( i.e. roots, stolons or tubers).

Management of white mold disease

Effective management of white mold requires implementation of an integrated disease management approach. The disease can be controlled primarily through the use of cultural practices and foliar fungicides.

Good fertility management to prevent excessive canopy development will also suppress white mold. As such, cultivars that naturally produce thicker, dense canopies are at higher risk of white mold, than those that produce sparser canopies.

Use of the biological control agent Conithirium minitans, a parasite of S. sclerotiorum sclerotia, to reduce the sclerotia bank in the soil has yielded conflicting results between the regions where the experiments were conducted.

The most widely cultivated commercial growers of potato are equally susceptible to Sclerotinia stem rot. In the absence of resistant cultivars, chemical control with fungicides remains the most effective management tactic. Successful fungicide products include Iprodione (a.i. iprodione), Botran (a.i. dichloran), Omega (a.i. fluazinam), Quadris (a.i. azoxystrobin), Topsin (a.i. thiophanate-methyl) and Endura (a.i. boscalid).

The long-lived sclerotia can be killed by flooding for about 5 weeks. Rotations with nonsusceptible crops, including potato only every third year, along with removal and destruction of infected plants, help reduce this disease. Avoid
overhead irrigation.

Field, greenhouse and in-vitro experiments have shown that there are no significant differences in the effectivness of these compounds. Using of these fungicides at initial full bloom are effective in reducing the number of infected stems.
However, using of the same fungicides made at or prior to row closure following label recommendations were found to offer erratic protection at best.

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