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Field Pea Diseases Review: Ascochyta /Mycosphaerella Blight: (06/02/16)

Ascochyta/Mycosphaerella blight can be an economically important disease when cool, wet weather occurs during bloom and pod-fill.

Field Pea Diseases Review: Ascochyta /Mycosphaerella Blight:

Importance.  Ascochyta/Mycosphaerella blight can be an economically important disease when cool, wet weather occurs during bloom and pod-fill. The disease is widespread throughout the growing region and spores can travel long diseases, which can place even new fields at risk.

Symptoms.  This disease complex causes dark necrotic lesions on leaves, stems, and pods, with symptoms most severe in the lower canopy.  Foliar symptoms develop as purplish-brown flecks and/or brown lesions with concentric rings; depending on conditions, either type of lesion or a mix of both types of lesions may develop.  Stem lesions, which typically develop only at the base of plants, are brownish-purple and can cause lodging and, when severe, premature senescence.  Ascochyta/Mycosphaerella blight is most easily confused with bacterial blight, a very different disease which is NOT managed by fungicides.  Consequently, accurate identification is critical.  An excellent and detailed resource to distinguish the two diseases is available on the NDSU Carrington Research Extension website

Disease Cycle and Development.  The pathogens causing Ascochyta/Mycosphaerella blight overwinter on crop residues and produce aerial spores in the spring.  These spores can travel long enough distances in the atmosphere that even fields with no history of field peas are at risk. The disease is most damaging when cool, wet weather occurs during bloom and early to mid-pod development.

Management.  Foliar fungicides can decrease yield losses to the disease and also significantly improve harvest ease by reducing the basal stem lesions that can cause lodging.  The optimal application timing generally coincides with full bloom and early pod development (when the first pods are still flat), but applying fungicides at bloom initiation may be advised if the canopy is very dense and conditions are highly favorable for disease (wet and cool).  A single fungicide application generally provides adequate control.  The triazole (DMI / FRAC 3) fungicide Proline and the strobilurin (QoI / FRAC 11) fungicides Headline, Quadris, and Aproach are effective and have performed comparably in research trials.  The SDHI (FRAC 7) fungicides Endura and Vertisan have exhibited reduced efficacy in research trials. 

When considering fungicides, producers should be careful to rotate fungicide chemistries when more than one application is made in a season, or when a single fungicide application is made in sequential seasons.  Low to moderate frequency of fungicide resistance to the QoI fungicides has been reported in parts of Montana and Alberta.  While this is not yet known to occur in our region, it serves as a cautionary note that these fungicides are vulnerable.  Also, it is important to note that the pathogens that cause Ascochyta blight on lentils and chickpeas are different pathogens, and that the widespread fungicide resistance to the Ascochyta blight pathogen on chickpeas is not relevant to field peas.

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Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

&

Julie Pasche

Research Plant Pathologist

NDSU Dept. of Plant Pathology

&

Michael Wunsch

Research and Extension Pathologist

NDSU Carrington REC

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