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Ascochyta blight on chickpea detected in the state - monitor for disease symptoms

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A four-part, composite picture showing chickpea, pea, and lentil leaves with tan-brown and brown lesions.

Ascochyta blight on pulse crops

Ascochyta blight is a serious, foliar disease of pulse crops and can diminish the crops under favorable conditions. The disease is caused by fungal pathogens that are specific to each pulse crop host: Didymella rabiei causes Ascochyta blight on chickpea and Didymella lentis infects lentils. Three pathogens cause this disease on peas: Didymella pisi, Peyronellaea pinodes, and Peyronellaea pinodella. Chickpeas are much more susceptible to Ascochyta blight and other fungal leaf blights. Pea and lentil are much more tolerant; yield is lost when there is significant foliar loss and stem breakage.

Symptoms

This disease can affect all above-ground plant parts, including stems, leaves, flowers, pods, and the seed. Infection can occur anytime during plant development if conditions are conducive. Lesions due to Ascochyta blight on chickpea are very distinct; they are circular or oblong in shape, and may begin as small, light-colored specks on the leaf which expand into target-shaped lesions (Figure 1). Each ‘wave’ of the lesion is surrounded by a brown to black halo, creating a bull’s-eye pattern over time. Lesions on pea tend to be more restricted, and the bull’s-eye pattern tends to be less obvious. Lesions on lentil are a lighter brown with a dark brown halo. Under moist conditions small, brown-black dots develop in the center of the lesions (called pycnidia) and are typically arranged in concentric circles. Lesions on plant tissue coalesce and cause defoliation, stem breakage and lodging.

Disease Development

The Ascochyta pathogens are seedborne and can survive on infected stubble for several years. In the spring, sexual spores (ascospores) are produced on field stubble or seed, which are wind-dispersed and can travel for up to five miles. Cool to moderate air temperatures of 59° to 77° F and wet environments favor disease development. Infection requires moisture on the plant surface for at least two hours and the likelihood of infection increases if plant tissue is wet for more than six hours. Symptom will develop several days after infection. The pycnidia developing in the lesions produce asexual spores (conidia), which are dispersed by rain or the moisture within the crop canopy and cause new infections. Ascochyta blight is a polycyclic disease which means that repeated infection cycles can occur for as long as conditions are favorable. This allows the disease to spread quickly through a field.

Ascochyta Blight Management (focus on chickpea)

An integrated management approach is required for an effective control of the disease and most strategies are implemented before or at planting. At this time in the season, disease monitoring and fungicide applications are the most relevant strategies.

Scout your crops frequently and carefully to detect symptoms of disease early.

Fungicide applications will be an integral component to control the disease under favorable conditions for disease development. It is important to carefully select fungicide products and rotate modes of action between consecutive applications to achieve good disease control and prevent fungicide resistance development in the pathogen population. Preventive fungicide applications, using contact fungicides (FRAC M) such as Chlorothalonil, are recommended before canopy closure/flowering to suppress disease development. At flowering or once disease symptoms are noticeable in the field, systemic modes of action need to be applied. Suitable modes of actions include Triazoles (FRAC 3) and Carboxamides (FRAC 7). Applications may need to be made in 10 to 14 day intervals, depending on rainfall patterns that favor disease development. Rotate fungicide FRAC groups between consecutive applications to prevent resistance development. Avoid using Strobilurin (FRAC 11) fungicide products as Ascochyta populations with resistance to this fungicide group have been detected in Montana. Application of a FRAC 11 fungicide to a resistant Ascochyta population will not effectively control the disease. Always apply fungicides at label rates and follow label restrictions. You can find information on suitable foliar fungicide products for Ascochyta and other foliar disease controls here: http://plantpath.msuextension.org/resources/index.html#fungicides

In all cases, when applying fungicides use labelled rates, water amounts, and nozzles where specified on the label. Nozzles for herbicide applications generally have larger droplet sizes. For fungicides, smaller droplets, although potentially increasing drift, provide better coverage and deposit on the leaf better than larger droplet sizes, increasing coverage and efficacy. Mixing multiple products in the tank can cause crop damage, so read labels of all products carefully before any application. Contact me to discuss fungicide application plans and efficacy of different products (they’re not all equal).

Pre-season management strategies:

Chickpea varieties differ in their resistance/susceptibility to Ascochyta blight. CDC Orion and CDC Frontier are more resistant to Ascochyta blight.

Diversify your crop rotation so that chickpeas are grown on the same ground only once every three years. Avoid growing chickpeas adjacent to fields that had chickpea planted the year before, especially if that field would be upwind (wind-dispersed ascospores).

Use disease-free seed. Plant certified, disease-free seed. The Ascochyta pathogens grow from the seed to the seedling and even a few infected seedlings can be a source of disease spread throughout the field due to its polycyclic nature. Keep in mind that infected seed may be symptomless. A 0% tolerance for Ascochyta on chickpea seed is recommended. For pea and lentil seed, Ascochyta incidence of less than 5% is advised. The Regional Pulse Crop Diagnostic Lab at Montana State University offers seed testing services: https://plantsciences.montana.edu/pulsecropdiagnosticlab/

A fungicide seed treatment is strongly recommended. Several seed treatment fungicides can suppress the seedborne pathogen and prevent early infection of seedlings. You can find information on suitable fungicide seed treatment options on the MSU Extension Plant Pathology Resources website: http://plantpath.msuextension.org/resources/index.html#fungicides 

Reducing crop density can reduce the humidity within the crop canopy and create a less favorable environment for disease development.

 

Picture Caption

Ascochyta blight symptoms on chickpea (A,B) lentil (C), and pea (D) (Picture credit: A,C - Mary Burrows, MSU; B,D – Sam Markell, NDSU)

 

Please don’t hesitate to email (uta.mckelvy@montana.edu) or call (406-994-557) if you have any questions. I’m here to help.

Best,

Uta McKelvy, Extension Field Crop Pathologist