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Archive for the ‘Diseases Caused by Fungi’ Category

Common diseases in garden

Tuesday, May 4th, 2010
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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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Thecaphora Smut

Thursday, September 10th, 2009

(Cased by Thecaphora (Angiosorus) solani )

Potato smut is restricted to the tropical regions of the America. It occurs in cool highlands and irrigated coastal deserts, where it may cause serious problems. Little is known about its biology.
Extreme care must be taken to avoid spreading the disease. Therefore, do not move infected tubers or infested soil to disease-free areas. Occurrence of this disease should be carefully recorded.

Symptoms of Thecaphora Smut

thecaphora-smutSymptoms are tuber-like outgrowths of stems and stolons that contain numerous small cavities filled with brown to black spores.
Potatoes tubers may contain small, inconspicuous superficial pustules with a few sporefilled cavities or large protuberances.
Single potato plants and even single stolons may carry tuber-like outgrowths as well as healthy-appearing tubers.
After maturity, diseased outgrowths disintegrate rapidly into masses of brown spores.
Certain potato cultivars such as Antarqui show protuberant lesions 3-10 mm in diameter on the tuber surface. A

fter 2-3 months of potatoes storage, these lesions become sunken and subsequently hypertrophied tissues develop in the new sprouts or close to them. Datura stramonium (jimson weed) is a sensitive and propagative host.

Management

Dissemination is probably by infected or contaminated seed and soil. Resistant or tolerant varieties exist. Crop rotations are useful although the fungus persists in fields for many years.

Strict quarantine should be enforced to prevent spreading the disease to new areas. Fumigation of infested soil, complemented with the use of healthy potato seed tubers of resistant potato cultivars, can eliminate the disease.

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Verticillium Wilt

Thursday, September 10th, 2009

(Verticillium albo-atrum, V. dahliae)

Verticillium wilts may be a serious problem in tropical and subtropical regions and irrigated deserts where water deficiency may be severe. V. dahliae is more severe during prolonged warm, dry weather in cooler regions of potatoes production.

Symptoms of Verticillium Wilt

This potato disease is characterized by leaf yellowing, which begins at the plant base and may develop unilaterally, restricted to the sides of leaves, the stem, or the plant.
verticillium-wiltLater, the plant may wilt. The vascular system of the lower stem turns brown. Potatoes plants frequently become yellowed and mature early without pronounced wilting (early dying).
Stems wilted by V. albo-atrum are blackened by the presence of a blackish resting mycelium.
However, when V. dahliae causes wilting, the lower portion of the stem becomes grayish because of the presence of microsclerotia.
The vascular ring of tubers may have light brown discoloration extending from the stolon end up to more than halfway through the potato tuber. Larger tubers often have light tan, discolored eyes (pink eye).
These fungi are long-lived in soil or plant debris and have a wide host range, including other solanaceous plants, cotton, and weeds.
Surface-borne inoculum on seed tubers is important in disease spread. Interaction with nematodes (Meloidogyne, Pratylenchus, Globodera), fungi Rhizoctonia, Colletotrichum, Fusarium), and bacteria (Erwinia) can increases damage.

Management

Use crop rotations with nonsusceptible cereals, grasses, or legumes. Resistant or tolerant potato varieties are available.
Treat potatoes seed tubers with disinfectant fungicides to remove soil-borne inoculum. Prevent water stress by irrigation.
Systemic fungicides are useful while growing potatoes.

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