Potato Review Group

Contents

Haulm destruction

Vascular browning and stem end necrosis

Haulm destruction and disease risk

Haulm destruction and skin set

Haulm destruction and tuber quality

Time from haulm destruction to harvest – influence on bruising

Further information:

Notes on harvesting

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Haulm destruction

Chemical haulm destruction

  1. The options for this are limited.
  2. Pyraflufen-ethyl (Gozai / Kabbuki) and carfentrazone-ethyl (Spotlight) are contact products.
  3. It may be possible to use these alone for desiccation IF the crop is already senescing.
  4. They can also be used in flail and spray programmes.
  5. Pyraflufen-ethyl and carfentrazone-ethyl have been shown to have similar efficacy to each other for desiccation of leaves and stems but there are restrictions to crops following pyraflufen-ethyl.

More …

Mechanical haulm destruction

  1. The main method of mechanical haulm destruction is flailing but pulling (a sharp, swift pull is required) and pulverising may also be performed. Flaming the canopy has also been investigated, particularly after mechanical treatment.
  2. Flail can provide quick removal of an immature canopy.
  3. A desiccant can then be applied to kill stems.
  4. The better the flail operation, the more effective will be the desiccant.
  5. The late blight control programme must be up to date before flailing, as flailed material and remaining stems can still be a source of blight infection.
  6. If flailing opens up cracks in ridges the risk of blight infection of tubers increases; ridge rollers can reduce this risk.
  7. Electric haulm destruction is being investigated. More …

More …

Influence of nitrogen

  1. Increasing rate of nitrogen application has a potential to increase canopy growth during canopy expansion.
  2. Experiments for the PRG have shown little influence of nitrogen on potential canopy duration.
  3. If the canopy senesces naturally, rate of nitrogen application may have little effect on the time to full senescence.
  4. The earlier in senescence canopy destruction is required, the greater may be the effect of nitrogen application.
  5. Use the PRG Nitrogen Model to ensure that excess nitrogen is not applied and see the Nitrogen page for further information.

More …

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Vascular browning and stem end necrosis

  1. Often associated with application of diquat in dry soil conditions, vascular browning and stem end necrosis can result from physiological shock as a result of rapid destruction of a vigorous, green canopy, particularly in dry soil conditions.
  2. Symptoms may occur as a result of chemical or mechanical haulm destruction and cultivars differ in susceptibility.
  3. Destruction of an immature canopy is difficult and may require a combination of chemical and mechanical treatments but soil moisture should be checked before treatment begins.
  4. If soil from the centre of the ridge, 5 cm below the lowest tuber, is too dry to form into a ball, there is a risk of poor tuber quality if an active canopy is killed rapidly.

More …

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Haulm destruction and disease risk

Potato late blight

  1. Blight spores may continue to be produced as long as there is live foliage.
  2. Movement of water through soil is required to move spores to tubers.
  3. If the canopy is dying slowly, blight fungicides should be applied until the latest date determined by the harvest interval.

Soft rots

  1. The main source of PCA is rotting tubers.
  2. There is a much lower risk of infection of tubers from blackleg infected plants.
  3. Transmission of PCC from haulm to tubers may occur if:
    • the haulm is not desiccated but is allowed to rot on the ground,
    • there is sufficient movement of water through soil to carry bacteria to the progeny tubers.

Black scurf

  1. The incidence of black scurf increases when skin set occurs.
  2. Reductions in black scurf have been shown by:
    • green top harvesting and re-burying tubers until skin set
    • loosening soil and separating tubers from plant residues

Gangrene

  1. Gangrene may be tuber borne or soil borne.
  2. Stems may become infected and this may contribute to infection of progeny tubers at harvest.
  3. Haulm pulling may reduce this risk of disease infection due to:
    • haulm removal
    • detaching tubers from plant residues
    • soil aeration

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Haulm destruction and skin set

  1. Skin set may be influenced by:
    • plant / skin maturity
    • soil moisture and temperature
    • cultivar
    • haulm destruction
    • and is likely to occur first at the stolon end of the tuber.
  2. The periderm is formed during early stages of tuber development and comprises three layers (phellem, phellogen and phelloderm).
  3. The skin remains immature during tuber growth and there is a constant addition of cells.
  4. Some changes to the periderm occur during tuber growth.
  5. The dry weight increases relative to the fresh weight.
  6. Most of the increase in resistance to water loss occurs before skin set and this is suggested to be related to deposition of lipids.
  7. Skin set is suggested to be initiated when tuber growth stops.
  8. The three layers of the periderm become bonded as the skin sets.
  9. Bonding of the three layers cannot begin until the phellogen (which produces the new cells) stops dividing.
  10. Skin set may be retarded in very dry or very wet conditions.
  11. The rate of skin set declines with declining temperature (there is a similar biochemical process to that during wound healing).
  12. The rate of skin set will be related to temperature and plant maturity at haulm destruction.
  13. Early haulm destruction, at warm temperatures, may result in rapid skin set but the rate may be reduced if the crop is immature.
  14. Late haulm destruction, when the crop is maturing naturally, may result in rapid skin set but the rate may be reduced if the temperature is low.
  15. Experiments for the PRG have shown little effect of nitrogen application on skin set if the canopy has senesced naturally. More …

For more information see: Skin set.

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Haulm destruction and tuber quality

Tuber dry matter concentration

  1. Tuber dry matter concentration increases with increasing tuber size and later dates of harvest.
  2. However, tuber dry matter concentration can change between the time of haulm destruction and harvest.

For more information see: Tuber dry matter concentration.

Concentration of sugars in tubers

  1. In general, the concentration of sugars in a tuber declines as the tuber grows.
  2. The larger the tuber and the later in the season, the lower will be the sugar concentration.
  3. However, stress may result in an increase in the concentration of reducing sugars, in particular.

For more information see: Processing quality.

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Time from haulm destruction to harvest – influence on bruising

  1. There are suggestions that susceptibility to bruising varies with time after haulm destruction.
  2. However it is difficult to find any data to quantify any such changes.

For more information see: Bruising.

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Further information

Notes on harvesting

Nutrition 2021 (Includes effects of nitrogen on canopy senescence and skin set)

Haulm destruction 2020 ( Relationship between maturity and skin set; flail and spray techniques; desiccants; future development)

Canopy destruction 2019 (Desiccation without diquat; flail techniques)

Canopy destruction 2013 (Risks of disease infections)

Haulm destruction 2011 (Information on diquat – now superseded)

Haulm destruction and vascular browning 2007 (Vascular browning can be caused by various haulm destruction techniques; information on desiccants has been superseded)

Haulm destruction 2005 (Information on physiological vascular browning and stem end necrosis is still relevant, information on desiccants has been superseded)

Haulm destruction 2001 (Information on mechanical haulm destruction is still relevant, information on desiccants has been superseded)

Haulm destruction 1999 (PRG research on tuber growth and quality after haulm destruction – still relevant)

Haulm destruction 1998 (Information on desiccants has been superseded)

Seminar 2 Notes 1992 (Chapter 6: Determining desiccation date in relation to tuber size.)

 

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