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Posts Tagged ‘potato’

Take care about potato storage between seasons

Wednesday, September 1st, 2010
Orka Vegetable Storage
Image by aMichiganMom via Flickr

Some pathogens, such as the silver scurf pathogen, may survive from one season to the next in the storage facilities themselves. Storages and handling equipment should be cleaned and sanitized or “disinfected” after the storage is emptied and before handling and storing the new crop. Disinfection of storages and handling equipment is a three-step process.

  • Remove dirt and debris. All the disinfectants approved for use in potato storages are rapidly tied up and rendered ineffective by dirt and organic matter. The next two steps of the process will be much more effective if the debris from last year’s crop is removed.
  • Wash with soap and water. This step is often accomplished with a pressure washer and a detergent solution. Warm or hot water will be more effective than cold water. Steam washers are also a good choice but will not actually disinfect storage surfaces or equipment because the duration of the exposure to steam is too short. Water and detergent help to dissolve and remove dried tuber sap and bacterial slimes that are deposited on storage surfaces and equipment, and detergents have some disinfection capability. Cleaned surfaces allow the disinfectant, used in the next step, to work properly.
  • Disinfect. Use an appropriate and registered disinfectant and make sure that the surfaces to be disinfected remain wet with the disinfection solution for at least 10 minutes. Use sufficient sprayer pressure and volume to effectively clean all surfaces.

Many fungal spores have tough, resilient cell walls, and bacteria in storages often occur in the form of dried slime. Ten minutes provides the necessary time for the disinfectant to penetrate the fungal cell wall or dissolve the bacterial slime and kill the pathogen.

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Minimization of risk Fusarium dry rot

Tuesday, April 27th, 2010

Fusarium dry rot is one of the most essential diseases of potato. It affects tubers in storage and seed pieces after planting. Fusarium dry rot of seed tubers can lessen crop establishment by killing developing potato sprouts.

Symptoms

The first symptoms of Fusarium dry rot are typically dark depressions on the surface of the tuber. In large lesions, the skin becomes wrinkled in concentric rings as the underlying dead tissue desiccates. Internal symptoms are characterized by necrotic areas shaded from light to dark chocolate brown or black.
This necrotic tissue is frequently dry (hence the name “dry rot”) and may increase at an injury such as a cut or bruise. The pathogen enters the tuber, often rotting out the center. Rotted cavities are often lined with mycelia and spores of various colors from yellow to white to pink depending on the species of the pathogen (several species of Fusarium cause dry rot).

Dry rot diagnosis may be complicated by the presence of other tuber pathogens. Soft rot bacteria
(Pectobacterium spp.) often colonize dry rot lesions, especially when tubers have been stored under conditions of high relative humidity or tuber surfaces are wet.

Soft rot bacteria cause a wet, slimy rot, which can rapidly engross the entire tuber and mask the initial dry rot symptoms. Dry rot also causes sprout death and when estimating the frequency of infected tubers growers should carefully examine the eyes (sprouts) to check if they are viable.

Measures to minimize contamination of Fusarium dry rot

Some level of Fusarium dry rot is almost constantly present in commercially available seed. Undergo the following procedures will help prevent dry rot:

  • Always plant only certified seed. It is critical to purchase seed with as little dry rot as possible, so always inspect seed carefully upon receipt.
  • After careful unloading, seed should be stored at 40° to 42°F and 85 to 90 percent relative humidity, and kept ventilated.
  • Warm seed tubers to at least 50°F before handling and cutting to reduce injury and promote rapid healing.
  • Sanitary and disinfect seed storage facilities systematically before receiving seed.
  • Disinfect seed cutting and handling equipment often, and make sure cutters are sharp to ensure a smooth cut that heals easily.
  • Do not store seed near a potential source of inoculum (e.g., cull piles).
  • Prior to seed treating (on conveyer to seed treatment hopper), grade out (remove) heavily infected tubers.
  • Treat cut seed with a seed treatment to control seed piece decay and sprout rot
  • Plant infected seed lots seed shallow (about 4”) in warm, well-drained soil to encourage rapid sprout growth and emergence, and lessen the chance for infection.
  • After emergence, plaints can be hilled to establish required bed depth.
  • In the fall, harvest tubers after their skins have set and when their core temperature is greater than 50°F.

Chemical control

Seed treatment
Several products have been produced specifically for control of seed borne potato diseases and offer broad spectrum control for Fusarium dry rot, Rhizoctonia, silver scurf and, to some extent, black dot These include Tops MZ, Maxim MZ (and other Maxim formulations + mancozeb) and Moncoat MZ.

The general impact of these seed treatments is marked by improved plant stand and crop vigor, but occasionally, application of seed treatments in combination with cold and wet soils can result in delayed emergence. The delay is generally transient, and the crop normally compensates.

The additional benefit of the inclusion of mancozeb is for prevention of seed-borne late blight.
Studies at MSU have shown that the most effective control of Fusarium dry rot is achieved by the application of an effective fungicide, such as fludioxinil (Maxim-based products), prior to planting.

Treatment of infected seed pieces with Maxim MZ (0.5 lb/cwt) at 10, 5 or 2 days before planting significantly reduced the percentage of diseased sprouts per tuber and significantly reduced seed piece decay.

Although it may not seem cost-effective to apply seed treatments to healthy seed, these results suggest that applying a seed treatment up to 10 days prior to planting can provide effective control of dry rot and increase rate of emergence, rate of canopy closure and final plant stand.

Postharvest fungicides
Mertect, thiabendazole remains registered for postharvest use on tubers. Few alternative compounds are available for potato tuber treatment in storage but include chlorine-based disinfectants such as sodium hypochlorite, calcium hypochlorite and chlorine dioxide. Limited information is available on the effectiveness of chlorine dioxide on potato storage pathogens, and results of some studies have suggested that chlorine dioxide does not provide effective tuber protection against Fusarium dry rot.

Some biological products have suppressed Fusarium dry rot in storage and include Serenade that is registered for foliar application to potatoes in the field.

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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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