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Faba Bean Diseases

Ascochyta Blight

  • caused by Ascochyta fabae
  • occurs everywhere faba bean is grown in western Canada
  • can be stubble or seed-borne
  • spread occurs from spores that ooze out of the pycnidia and infect nearby plants through rain splash

Symptoms

  • most important symptom is spots on the leaves, stems and pods
  • on leaves, spots are circular, up to 1 cm in diameter and usually tan coloured ** characteristic small, black fruiting bodies (pycnidia) of the fungus form in most spots and are concentrically arranged (at a later stage, many spots merge into irregular black patches)
  • on stems, spots are usually reddish-brown and more elongated
  • on pods, spots are similar to those on leaves but usually more sunken, tan to black coloured in the centre and bordered by a dark brown margin (pycnidia are again readily observed within the spots)
  • seeds from infected pods are regularly infected and may be discoloured and shrivelled

Prevention and Control

  • use disease-free seed and practise a four to five-year crop rotation
  • avoid seeding next to previous year’s faba bean fields since ascospores can travel long distances by wind
  • plowing or discing to bury all crop residue as soon as possible after harvest will also help prevent the fungus from being dispersed by wind and rain
  • no fungicides are registered in Alberta for control of ascochyta blight

Chocolate Spot

  • caused by two fungi: Botrytis fabae and Botrytis cinerea
  • most prevalent under warm, wet conditions
  • both fungi can be stubble or seed-borne
  • spores (conidia) are produced on infected lower leaves and dead plant tissue
  • conidia are spread to neighbouring plants and fields by wind and rain, where they cause new infections (water is essential for their germination)

Symptoms

  • occurs on leaves, stems and pods as brown markings
  • lesions on leaves vary from small reddish-brown dots to well-defined areas with reddish-brown margins and tan-coloured centres.
  • later, lesions become entirely reddish-brown – under favourable conditions, the disease becomes aggressive and lesions may merge causing blackening and partial defoliation

Prevention and Control

  • use disease-free seed and a four-year crop rotation
  • plow under crop residue

Powdery Mildew

  • caused by Microsphaera penicillata var. ludens
  • usually appears late in the growing season and can occasionally cause serious yield losses
  • overwinters on infected crop residue and as cleistothecia
  • disease is favoured by high humidity and warm weather
  • rain and irrigation causes spores to burst instead of germinating which prevents disease development

Symptoms

  • first shows up as small spots of powdery growth on the upper surface of leaves, which continue to enlarge, eventually covering the entire leaf surface with a white powdery mass
  • the bottom of the leaf beneath the affected area may turn purplish, then brown
  • later in the season, small oval fruiting bodies (cleistothecia) can be seen embedded in the white fungal growth – these are yellow at first, then gradually turn orange to brown and ultimately black

Prevention and Control

  • do not plant faba bean on the same field more than once every four years
  • bury all crop residue and locate new fields away from fields where faba bean was planted the previous year
  • no fungicides are registered to control this disease in faba bean

Root Rot & Seedling Blight

  • caused by Rhizoctonia solani and Fusarium spp.
  • occurs wherever faba bean is grown in western Canada
  • occurs on the root hairs and the main root, as well as the lower part of the stem and may even extend a short distance above the soil surface
  • pathogen overwinters on crop residue and in the soil

Symptoms

  • infected areas are greyish-brown to black – infection often begins on the feeder roots and progresses gradually towards the main root (in some cases, all roots are destroyed)
  • symptoms on foliage are also progressive, ranging from a few yellow leaves to pronounced yellowing of the top growth and severe stunting
  • if infection occurs early, it can cause seed rot and pre- and post-emergence damping-off – seedlings will sometimes show a constriction of the stem at or near the soil line
  • infected seedlings usually die, resulting in poor stands

Prevention and Control

  • follow a crop rotation that does not include faba bean or other legumes (pea, lentil, bean, alfalfa, clovers) more than once every four to five years
  • ensure good soil fertility to produce a vigorous crop stand
  • no fungicides are presently registered for control of this disease in faba bean

Rust

  • caused by Uromyces viciae-fabae
  • occurs only occasionally on faba bean in western Canada
  • overwinters on seed or infected crop residue
  • can also infect lentil, pea and vetch, and these can become sources of inoculum
  • produces five different kinds of spores: pycnidiospores, aeciospores, urediospores, teliospores and basidiospores
  • teliospores are the most resistant and can survive up to two years under adverse conditions
  • teliospores germinate in the spring and produce basidiospores that infect healthy fababean plants; urediospores (summer spores) are then produced on infected plants and are responsible for the rapid secondary spread of the disease to plants in the same field or long distances away
  • both high relative humidity and late application of irrigation contribute to this disease

Symptoms

  • easily recognized by rust-coloured, blister-like spots (uredo sori) on leaves and stems – these sori eventually blacken due to production of another kind of spore
  • a chlorotic halo may also be present around each sori, further reducing the photosynthetic area of the plant, and premature defoliation may occur

Prevention and Control

  • follow a crop rotation of four or more years between faba bean crops to prevent disease build-up
  • no fungicides are registered for control of this disease in faba bean

Sclerotinia Stem Rot

  • caused by Sclerotinia sclerotiorum
  • considered of minor importance on faba bean in western Canada
  • overwinters as sclerotia in infected crop debris and soil
  • small golf tee-shaped structures (apothecia) grow on the sclerotia and produce spores that infect healthy plants
  • disease is favored by cool, moist conditions such as those found under a thick canopy

Symptoms

  • first appears on the stem near the soil surface as a water-soaked area that spreads both upwards and downwards
  • the affected area appears bleached and later turns light brown
  • stems, when split open, exhibit characteristic white fungus growth – numerous, black, hard resting bodies (sclerotia) may be present in the pith
  • affected plants yield poorly and often die prematurely

Prevention and Control

  • a four to five-year crop rotation between faba bean and other susceptible crops (canola or mustard, sunflower, dry bean, pea or lentil) is recommended
  • burial of crop residue will also prevent sclerotia from germinating
  • no fungicides are registered for control of sclerotinia stem rot in fababean at this time

Bean Yellow Mosaic

  • caused by bean yellow mosaic virus (BYMV)
  • two variants of the virus have been identified: mild (leaf mosaic with no necrosis) and severe (leaf mosaic with necrosis)
  • virus is spread from overwintering hosts such as clovers and vetch to faba bean by aphids

Symptoms

  • affected leaves show leaf mottling and mosaic (diffuse light and dark green or yellow or green areas) – further leaf symptoms are leaf rolling or cupping, necrotic (localized dead tissue) leaf spotting and necrotic stem streaking ultimately extending up to the shoot tip
  • some plants also exhibit pod splitting and stunting
  • infected plants may ultimately die

Prevention and Control

  • do not plant in close proximity to fields of clover and other perennial legume crops

Aster Yellows

  • caused by aster yellows mycoplasma-like organism
  • common on faba bean throughout western Canada, but usually no more than 1 to 2 per cent of plants are affected so economic losses do not occur
  • transmitted by leafhoppers from infected perennial weed hosts or carried with leafhoppers as they migrate north from the United States

Symptoms

  • leaves turn yellow, first in the areas between the veins and then throughout the entire leaf, and death of leaves occurs from the margin in (defoliation of lower leaves can result)
  • stunting and flower formation failure can also occur
  • if plants are infected late in the season, upper pods may fail to set seed

Prevention and Control

  • seeding early can help to prevent early infections
  • controlling weeds around fields may help reduce local sources of infection

Grey Mold

Caused by Botrytis cinerea Pers. ex Fr., Grey Mold can be seed-, stubble- , air- and soil-borne and can attack at various stages of plant growth. Infected seed produces infected seedlings, which die before emergence or soon after. On older plants, a greyish mold is observed, which quickly spreads under moist conditions.

Causes

  • Cool temperatures
  • High humidity
  • Wet soils
  • Dense canopies

Symptoms

On young plants that emerge, the Grey Mold appears as a grey moldy growth visible at the soil surface. On older plants, it appears as a fuzzy grey or dirty white moldy growth on flowers, pods, or lower areas of the stem. The infected sites first develop small water-soaked lesions that expand to form large brown lesions with concentric zones. Under humid conditions, massive greyish-brown spores are produced to cover the infected tissues. Sometimes, black sclerotia may be formed on old infected tissues. These lesions spread to the entire lower foliage. As the disease progresses, wilting, premature ripening, failure of pods to fill, and dead infected crop areas occur.

Treatment & Prevention

  • Treat seed or plant disease free seed.
  • Widen row spacing or lower seeding rates to improve air circulation in the crop.
  • No fungicides are registered for control in many of the pulse crops.
  • Potassium fertilizer in potassium deficient soils reduces the severity of Grey Mold.

White Mold

Often called White Mold or pod rot, Sclerotinia rot is caused by Sclerotinia sclerotiorum. The critical infection period is during the flowering stage. While White Mold is of minor importance in the most of pulse crops, it can cause severe losses in bean, where the infection can spread quickly. Sclerotinia overwinters in infected crop debris and soil.

Causes

  • Cool temperatures
  • High humidity
  • Dense canopies
  • Growing pea and canola in the same rotation

Symptoms

The first sign of White Mold is the appearance of a light brown, water-soaked discolouration on the stem, leaves, or pods and a cottony threadlike growth in the collar region if the temperature and humidity levels remain high. A water-soaked area appears that spreads both upwards and downwards. Dark brown spots then develop on the stem, and the entire plant eventually turns brown. Affected plants often appear wilted and ripen prematurely due to rotting stems; lodging is common in affected areas. Stems, when split open, exhibit characteristic white fungus growth — numerous, black, hard resting bodies (sclerotia) may be present in the pith. Affected plants yield poorly and often die prematurely.

Treatment & Prevention

  • Bury all crop residues.
  • Fungicide use for control of Sclerotinia stem rot in the majority of pulse crops is not cost-effective because, once the canopy closes, the fungicides cannot reach their target.