Potato Review Group

Contents

Biology of Alternaria

Identification

Crop interactions

Control

Integrated control programme

Further information:

Early blight notes

 

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Biology

  1. Alternaria occurs in most areas where potatoes are grown but is usually less aggressive than is late blight caused by Phytophthora infestans.
  2. Spores can be wind blown and are longer lived than those of late blight.
  3. Disease development is encouraged by warm, moist conditions and in hot environments may be more prevalent than late blight.
  4. Infection usually occurs on senescent leaves but can also occur early in the season.
  5. Tubers can become infected through wounds at harvest.

More …

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Identification

  1. Target spot type lesions on foliage are a classic symptom.
  2. The disease is difficult to identify correctly without analysis of lesions and the spores produced.
  3. Alternaria solani is the cause of true early blight but Alternaria alternata and Cladosporium may colonise lesions caused by nutrient deficiencies or stress.
  4. Interactions between Alternaria solani strains and potato cultivars vary and A. alternata may cause foliar symptoms indistinguishable from those of A. solani.
  5. Lesions caused by nutrient deficiencies and stress can also appear similar to A. solani lesions.
  6. Alternaria solani is not a frequent disease in the UK, so potential infections should be identified before fungicides are applied. More …

More …

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Crop interactions

  1. Stressed crops are more susceptible to infection. More …
  2. Cultivars differ in resistance but there is limited reliable information as the disease has not been identified in all trials. More …
  3. Some research suggests that early maturing cultivars are more susceptible than are late maturing cultivars. More …
  4. The cultivar “Markies” is regarded as being particularly susceptible but can produce early blight type symptoms in the absence of Alternaria infection. More …
  5. Yield losses are most likely if infection occurs early in the season. More …
  6. Infection during senescence may cause minimal yield loss. More …

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Control

Cultural control

  1. Avoid nutrient and drought stress; this may be the most effective means of reducing infection by Alternaria alternata. More ...
  2. There is some evidence that application of zinc can help to reduce susceptibility to infection by Alternaria spp. More … 
  3. Ensure good skin set and careful harvesting of any infected crops, to reduce the risk of tuber infection during harvest.
  4. Do not save seed from infected crops; the disease can be seed borne.

Timing of chemical applications

  1. Early and preventative applications are more effective than curative applications.
  2. Timing of application is important but difficult to judge if only a couple of applications are to be made.
  3. Susceptible cultivars may need prophylactic applications, beginning before flowering.
  4. In a susceptible crop a higher number of applications increases the likelihood of making an application at the right time.
  5. For potentially susceptible cultivars the first treatment should be at the onset of senescence, flowering or at the first sign of Alternaria solani (be sure that the lesions are caused by this species).

More …

Options for chemical control

  1. Fungicides have less effect on Alternaria alternata than on A. solani. More …
  2. Difenoconazole can provide effective control of early blight; difenoconazole + mandipropamid can provide control of early and late blight. More …
  3. Use of mancozeb in a late blight control programme can help to control early blight. More …
  4. However, it is unclear for how long application of mancozeb will still be permitted in the UK (March 2021).
  5. Addition of a drift retardant (e.g. “Sterling” / “Crusade”) can enhance control. More …
  6. N.B. Resistance to strobilurin fungicides (e.g. pyraclostrobin) and SDHI fungicides (e.g. boscalid) has been found in Europe. More …

Control of Phytophthora + Alternaria.

  • mandipropamid + difenoconazole
  • “Amphore Plus”  / “Carial Star” (Syngenta)

Options for control of Alternaria only.

  1. difenoconazole
    • e.g. “Narita” (Belchim Crop Protection Ltd)
  2. pyraclostrobin + boscalid
    • “Signum” (BASF)
    • EAMU for Alternaria control

See the manufacturers’ websites for details of fungicide use.

 

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Integrated control programme

  1. A possible programme for integrated control of Alternaria spp. More …
  2. It is unclear for how long application of mancozeb will still be permitted in the UK (March 2021).

Possible programme for early blight control

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Further information

See the manufacturers’ websites for details of agrochemical use.

 

Early blight notes

Control of early blight (Alternaria spp) 2020 (Frequency and identification; cultivar susceptibility; integrated control)

Early blight 2019 (Effects of fungicide resistance in Europe)

Early blight 2018 (Development of disease in relation to canopy maturity; experiment with drift retardant)

Control of Alternaria spp 2017 (Experiment with drift retardant; number of fungicide applications; variation in pathogenicity of different strains; potential fungicide options)

Adjuvants for potatoes 2017 (Enhancement of control with “Sterling” / “Crusade” [IA021] drift retardant)

Early blight 2016 (Symptoms are difficult to identify correctly by eye; fungicide resistance in Europe)

Control of early blight 2015 (Assessing the risk of infection)

Early blight 2014 (Comparison between Alternaria solani and A. alternata; disease development in the canopy; influence of nutrition; time of fungicide application)

Early blight 2013 (Control of Alternaria solani and A. alternata; risk of fungicide resistance, modelling disease development)

Early blight biology and control 2012 (Time of starting a control programme; difenoconazole + mandipropamid for control of early and late blight)

Early blight update 2011 (Conditions conducive to infection; cultivar susceptibility)

Early blight 2010 (Recognising and controlling early blight)

Early blight control 2009 (Alternaria life cycle; control should be in addition to a late blight programme)

Early blight 2004 (Symptoms; conditions for disease development; yield loss)

 

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