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Posts Tagged ‘management’

Mosaics

Friday, September 11th, 2009

(PVX, PVS, PVM, also PVY and PVA)

Mosaic symptoms may be caused in potato leaves by several different viruses, singly or in combination.
mosaicsSome of these are potato virus X (PVX), potato virus S (PVS), and potato virus M (PVM), as well as PVY and PVA.
PVX may cause yield losses above 10%, with the extent varying according to strain and potato cultivar.

It is transmitted through infected tubers and by contact (not by aphids), and normally causes mosaic.

Infection may be mild in some cultivars and is frequently latent. Virulent strains may cause crinkling. Some cultivars are hypersensitive to certain strains and react with top necrosis.
PVS is common and may cause mild symptoms.

It has little effect on yield. It is transmitted through infected tubers, by contact, and by aphids in some strains.
Infection is normally latent although some cultivars react with mild mosaic or faint vein banding.
A few sensitive potatoes cultivars react with severe bronzing, necrotic spotting, or even leaf drop.
PVM is less common than PVY, PVX, or PVS, and little is known about its effects on yield. It is perpetuated by infected tubers and transmitted by contact and by aphids.
The virus is latent in some potatoes cultivars although in others it causes a mild mosaic or even a severe mosaic and leaf crinkle.
Under certain environmental conditions, sensitive cultivars may also develop necrosis of petioles and leaf veins.

Management of Mosaics potato disease

PVX, PVS, and PVM are controlled by clonal selection during seed multiplication. Roguing is useful only when obvious symptoms develop.
Cultivars resistant to PVX for growing potatoes are available.

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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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