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Posts Tagged ‘symptoms’

Symptoms of nutrient imbalance of potato plants

Friday, September 11th, 2009

Potatoes grow best in soils of pH 5.0 to 7.0. Deficiencies or toxicities of major or minor elements may be caused by excessive solubility or fixation in the soil through interaction with soil colloids or chemicals.

Nitrogen (N) requirements increase rapidly with potatoes plants growth.
When N is translocated to upper leaves excessively from the lower leaves, they then become yellow.

Later, if the deficiency is not corrected by fertilization, the entire potato plant becomes yellow and fails to grow properly.

Severity of plant response depends on the level of N deficiency. N toxicity from ammonium or nitrites may follow degradation of nitrogencontaining fertilizers in certain soil conditions.

Potato-imbalancePhosphorus (P) deficiency follows P fixation in a wide range of soil types.

Symptoms include retardation in growth of terminals; small, spindly, somewhat rigid plants with crinkled or cup-shaped leaves; darker than normal colour; possibly a delay in maturity; and reduced yield.

Potatoes tubers may have internal rusty brown necrotic flecks similar to internal heat necrosis.
Because P is frequently fixed in the soil, fertilizer banding applications lateral to the seed piece are superior to broadcasting.
Potassium (K) deficiency is common in light, easily leached soils.

Early symptoms are dark or bluish green glossy foliage.
Later, older leaves of potatoes plants become bronzed and necrotic (superficially resembling early blight), and senesce early.
Necrotic, somewhat sunken corky lesions form on the tuber surface, particularly at the stolon attachment.
Potatoes tubers are predisposed to black spot, and when cooked tend to darken.

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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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Fusarium Dry Rot and Wilt

Thursday, September 10th, 2009

(Fusarium spp.)

Different Fusarium species distributed worldwide cause various problems. Warm temperatures favours this disease.

Symptoms of Fusarium Dry Rot and Wilt

Dormant Oil & Lime Sulfur
Dry rot is one of the most serious potatoes storage problems. Tubers initially have dark, slightly sunken lesions that later expand superficially, leaving internal cavities that may contain different colour mycelia, depending on the species involved.
The margin of the rot is clearly defined.
Concentric rings appear on the potatoes tubers surface and external mycelium is evident.
Potatoes tuber dries and hardens.
Under humid conditions, secondary soft rot develops. Infection originates in surface fusaruim-dry- rot-wiltwounds during harvest and handling.
It can be reduced by initial curing at about 15°C and 95% relative humidity to promote wound suberization, prior to cold storage.
Improperly suberized cut seed decays under adverse soil conditions.
Potato plants may fail to emerge, or be weak and subsequently wilt and die.
Fusarium wilt fungi are soil-borne.
Symptoms are yellowing of lower leaves, chlorotic mottle of upper leaves, and subsequent wilting.
Vascular tissues of stems and tubers become discolored.
Potatoes tubers show several types of internal and external discoloration such as brown sunken necrosis at the stolon attachment or eyes, and circular brown rotted areas.
Warm weather enhances wilt. Some Fusarium strains become systemic and are seed transmitted.

Management

Use disease-free potatoes seed, good water management, and crop rotation. Treat cut seed with chemical protectants.


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