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Management Recommendations for Ascochyta Blight on Chickpea (06/28/18)

We have had many questions about Ascochyta blight on chickpea in the last couple weeks. The disease is, by far, the most damaging disease to chickpeas.

Management Recommendations for Ascochyta Blight on Chickpea

We have had many questions about Ascochyta blight on chickpea in the last couple weeks. The disease is, by far, the most damaging disease to chickpeas. The information below is a summary of management recommendations for the disease. Ascochyta blight can cause complete crop loss in chickpeas even on fields with no prior history of the disease. Simply, every chickpea field is at risk for Ascochyta blight.

What is Ascochyta blight?

The disease is caused by the fungus Ascochyta rabiei, and is specific to chickpeas. Critically, a different Ascochyta species cause disease on each of the pulse crops. Consequently, this pathogen is not the causal agent of Ascochyta blight on either lentils or field peas. Similarly, the pathogens that cause Ascochyta blight on lentils and field peas do not cause disease on chickpeas.

Why is my field at risk?

The disease is seed-borne and is transmitted from seeds to the emerging seedlings. It is also introduced to new fields through atmospheric movement of spores. The causal pathogen produces infective spores on overwintered diseased chickpea residues, and the wind-dispersed spores can move miles away from their original source.

The use of chickpea seed that has tested negative for seed-borne Ascochyta combined with seed treatment with fungicides that suppress the transmission of Ascochyta from seeds to seedlings reduces the risk of Ascochyta development from diseased seed but does not eliminate that risk. When seed is tested for seed-borne Ascochyta, testing is conducted on small samples of seed, and the tests can fail to detect low levels of seed-borne disease. Seed treatment fungicides reduce, but do not eliminate, seed-to-seedling transmission of the disease. Even when seed testing negative for seed-borne Ascochyta is planted and that seed is treated with a fungicide seed treatment that suppresses seed-to-seedling transmission of Ascochyta, the introduction of Ascochyta blight into a field from diseased seed is possible.

What are the symptoms and signs?

Ascochyta blight initially develops as a few small scattered disease lesions within the canopy during mid- to late vegetative growth or early bloom, often at low incidence. These lesions begin as small gray specs that quickly turn into brown lesions with dark borders. Small, circular black dots (pycnidia) appear in the lesions, and are arranged in concentric circles, often resembling a bull’s eye. Lesions can occur an any above ground plant part; leaves, stems, flowers, etc. (Figures 1-4).

What conditions favor disease?

Ascochyta blight will develop rapidly in cool/moderate temperatures (59 – 77 F is optimal) and wet environments. Once infection begins in a field, frequent rainfalls will spread the disease very rapidly because spores released by pycnidia are splash dispersed. Periods of hot dry weather will slow or stop the spread of the disease, but spread will resume as soon as conditions become favorable again.

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How do we manage the Ascochyta blight?

Fungicide timing:

In very susceptible varieties such as ‘Sierra’ or ‘CDC Xena’, the disease can spread significantly even prior to bloom initiation when the canopy is completely open, and use of these varieties is not recommended in the Northern Plains. In more resistant varieties such as ‘CDC Frontier’ or ‘CDC Orion’, significant spread of disease generally does not occur until bloom when the canopy begins to close, trapping humidity. Ascochyta blight can be difficult to control once significant disease development has occurred, and a foliar fungicide application during early bloom is advised. Subsequent fungicide applications should be made at 10- to 14-day intervals as needed on the basis of rainfall patterns.

                Fungicide efficacy:

  • The pathogen causing Ascochyta blight has developed resistance to the QoI (FRAC 11) fungicides, and the fungicides Headline (pyraclostrobin), Quadris (azoxystrobin), and Aproach (picoxystrobin) have no efficacy against the disease.
  • DMI (FRAC 3) fungicides differ in effectiveness against Ascochyta blight. Proline (prothioconazole) is more effective than Quash (metconazole), and older DMI fungicides such as propiconazole (sold in the premix product ‘Quilt’) have little or no efficacy against Ascochtya blight.

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  • SDHI (FRAC 7) fungicides have shown equivalent efficacy to Proline when disease pressure is low to moderate but are less effective than Proline when conditions are highly favorable for disease.
  • Tank-mixing Proline or SDHI fungicides with chlorothalonil (Bravo WeatherStik, Echo 720, and other brands) improves Ascochyta disease control and can significantly improve chickpea yield and quality under disease pressure. Tank-mixing with chlorothalonil is advised for all fungicide applications, even those made after the canopy is closed. When tank-mixing, apply chlorothalonil at the low end of the labeled rate (generally 1.38 pt/ac) and maintain the full labeled rate of tank-mix partner.
  • Two or more fungicide applications are often needed, and DMI (FRAC 3) and SDHI (FRAC 7) fungicides should be rotated in order to reduce the risk of the development of fungicide resistance.

 

Michael Wunsch

Research and Extension Pathologist

NDSU Carrington REC

 

Julie Pasche

Research Plant Pathologist

NDSU Dept. of Plant Pathology

 

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

 

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