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Posts Tagged ‘symproms’

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.


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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Black Rot

Thursday, September 10th, 2009

(Rosellinia sp.)

Black rot, in higher tropical altitudes, may cause heavy potato yield losses in moist soils rich in organic matter (recently cleared land) and may affect other crop and weed hosts.

Symptoms of Black Rot

Black-rotDiseased potato plants are stunted and wilt. Underground organs develop a black rot partially covered by matted strands of grayish white mycelium.

The blackened potatoes tubers in cross section show a band of striate projections penetrating into the flesh. Often, only isolated potato plants are affected or the disease occurs in patches in the field. Only during lack of crop rotation while growing potatoes does the disease become a major problem.


Removal or burning of brush and trees when land is cleared and subsequent crop rotation are recommended control measures.

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Stem Rot Potato disease

Thursday, September 10th, 2009

(Sclerotium rolfsii)

Stem rot, southern blight, or Sclerotium rot occurs worldwide and attacks a wide range of potatoes plants, but is a problem for potato only while growing under hot, moist conditions.

Symptoms of Stem Rot

Initially, daytime wilting and yellowing result when brownish lesions girdle the stem base just below the soil line.

A white mycelium grows on potatoes stems, tubers, or soil, often in fan-like mats, which produce small, initially white, but later brown, sclerotia, similar in appearance to mustard seed.

stem-rotIn rainy weather, the affected stem sloughs off, leaving only the vascular tissue of the xylem, which leads to stem collapse.
Potato tubers may rot in the field before harvest, in storage, or in transit. They first form a cheesy semi-firm decay, which is often invaded by soft rotting organisms. Seed tubers may decay before plant emergence.


Sclerotia are long-lived and many crops are susceptible to S. rolfsii.
Control of stem rot is difficult when conditions favour disease.

Either plow deeply to bury affected plants and crop residues or remove them from the field and burn or bury them.
Avoid plant debris around potato stems.

The pathogen is highly aerobic; therefore, deep plowing and rotation with paddy rice are effective.
Harvest  potatoes during dry weather.
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