Disease Management

There are only a few diseases that significantly affect chickpea. Ascochyta blight is a foliar disease that can completely destroy a chickpea crop with up to 90 per cent yield loss in kabuli and 50 per cent yield loss in desi chickpea. It can also affect seed quality resulting in lower grades. It is much more aggressive than ascochyta blight in lentil or pea, and is caused by a different ascochyta species.

The pathogen overwinters on chickpea residue and seed. Both asexual spores and sexual spores can be produced on the residue. The sexual stage produces ascospores, which can spread several miles in the wind and are believed to be responsible for early season lesions. These ascospores are produced by genetic recombination, meaning the population can become genetically diverse. Research carried out at Agriculture and Agri-Food Canada, Saskatoon, has identified 15 races of Ascochyta rabiei in Western Canada. This not only makes breeding for resistance more of a challenge, it increases the likelihood of fungicide-resistant strains developing.

Symptoms include tan or brown lesions on stems, leaves and pods. The lesions may girdle entire stems, causing them to wilt and die. Dark fruiting bodies, called pycnidia, are formed in the lesions. The pycnidia ooze spores in wet and humid conditions. Spores are spread by rain, thus infection is aided by weather with frequent showers. Plants will show lesions approximately four to seven days following infection. If weather turns warm and dry, infected plants may survive, but will be delayed in maturity and produce lower yields. Ascochyta blight is also seed-borne, so the use of disease free seed is critical. It is also capable of surviving for several years on crop residues in the soil. A minimum four-year crop rotation will reduce the risk of infection.

Fungicides registered for control of ascochyta blight in chickpea work in two ways: protective and curative. Protective fungicides work to control disease by creating a barrier on the plant’s surface to prevent the spores from germinating and infecting the tissue and are most effective if they are applied preventatively, or before the fungus penetrates the plant. Curative fungicide activity is limited to the early part of the infection, and only for the first 24 to 36 hours after spore germination and infection. These curative products do not repair tissue that has already been damaged or killed by the fungus. No fungicide will protect against disease already established in the plant or once lesions form. All fungicides will protect against spores entering the plant (protectant activity) while only some products have curative activity. Fungicides that are currently available will provide protection against disease for no longer than two weeks. Refer to individual labels for more information.

The following are some key guidelines to a good integrated pest management program for ascochyta in chickpea:

  • Rotation: Three- to four-year crop rotation to non-host crops is necessary to reduce spores from previous crop stubble.
  • Field Choice: Avoid planting chickpea adjacent to previous year’s chickpea fields to reduce spread of residue and wind-borne spores and use non-host strips at field edges. Field selection should be at least 500 metres away from fields that had a chickpea crop the previous season.
  • Type of Chickpea: Choose class based on risk of ascochyta. Kabuli chickpea is much more susceptible to ascochyta blight compared to desi chickpea. Unifoliate Kabuli varieties appear to be much more susceptible to severe ascochyta blight, compared to fern leaf Kabuli. 
  • Variety Choice: Choose varieties that are as disease resistant as possible. Currently the best resistance level available is fair, and therefore, select varieties with a “fair” rating for ascochyta, instead of “poor” or “very poor”..
  • Seed Quality: Plant seed that has zero levels of ascochyta, or levels below 0.3 per cent ascochyta rabei. Use seed treatments if needed.
  • Seeding Rate: Target optimum plant densities (Kabuli 38-44 plants/m2, Desi 44 to 50 plants/m2). Increasing plant density above the recommended range with highly susceptible varieties can increase disease severity.
  • Fungicide Use: First application at early seedling stage is critical to prevent or slow early development. Follow up field scouting and additional fungicide applications may be necessary.
  • Scout Often: begin at the seedling stage, two to three weeks after seeding. Scout every three to seven days during the seedling stage. Rain and/or high humidity means scouting frequency should be increased. If conditions are drier and the chickpea plant gets past the seedling stage, scouting frequency can be decreased to every seven to 10 days.

A disease decision support checklist for ascochyta has been developed to aid in determining risk rating to ascochyta, and to determine appropriate management strategies.

Table 1. Determining Your Disease Risk 

1)  Review the following six considerations and assign a risk value to each.
2)  Add up the risk values to create a total risk value.

1. Field History and Crop Rotation

a. Crop is being grown in a region that has never had chickpea production

b. Crop is planted on land that has not had chickpea for at least three years.

c. Crop is planted on land that has had chickpea in the last two years; OR is located adjacent to chickpea stubble from the year before.

Risk Value

0

5

10
 

2. Chickpea Variety

a. Desi variety or kabuli variety rated as “fair” resistance to ascochyta blight (e.g. B-90 or Amit, CDC Frontier)

b. Kabuli variety that is rated as "poor"

c. Kabuli variety that is rated as "very poor"

Risk Value

5
 

10

20

3. Level of Seed-born Disease and Use of Seed Treatment

a. Seed test indicated no seed-borne ascochyta AND used registered seed treatment for ascochyta blight control

b. Seed test indicated low levels of ascochyta (<1%) AND used registered seed treatment for ascochyta blight control

c. Seed test indicated significant levels of ascochyta blight (5-10%) AND used a registered seed treatment for ascochyta blight control

d. The seed quality is unknown, OR I am not using a seed treatment

Risk Value

0
 

5
 

10
 

20

4. Presence of Disease Symptoms since last Fungicide Application

 a. No new disease lesions have developed since last fungicide application

b. Disease lesions have developed on new crop growth since last fungicide application

c. Leaf and/or stem lesions have developed and no fungicide has been applied this season

Risk Value

0

10

20

5. Weather Conditions

a. No rainfall in the past week and short-term forecast is for continued dry weather

b. Weather conditions are unknown

c. Rainfall or heavy dew has occurred during past week

d. Weather is unsettled, thunderstorms likely

Risk Value

5

10

20

20

6.    Other Crop Health Considerations

a. Crop emerged well in the spring and there has been no significant weather/injury to crop

b. Crop was seeded very early and was slow to emerge

c. Crop was damaged by early herbicide application or soil residue

d. The crop has received a light to moderate hail shower in the past 24 hours

Risk Value

0

5

10

10

                TOTAL RISK VALUE 1+2+3+4+5+6=                                       

Source: Saskatchewan Ministry of Agriculture’s Scouting and Management of Ascochyta Blight in Chickpea

Total Risk Value is < 15:

Your risk is low and ascochyta blight should not have a negative impact on your crop if you remain diligent about scouting and applying fungicides when necessary.

Consider the following recommendations:

  • Apply fungicide if the crop is at the seedling stage and a fungicide has not yet been applied.
  • Delay fungicide application if there has been no new lesion development and there is no rain in the forecast.

Total Risk Value is 20 to 45:

Your risk is low to moderate. Continue to scout for new lesion development as your crop matures. Consider the following recommendations:

  • Apply fungicide if it has been close to 14 days since the last application.
  • Delay fungicide if less than 14 days since last application and there is no rain in the forecast.

Total Risk Value is 50 to 75:

Your risk is moderate and disease is either increasing in your crop due to favourable weather conditions, or because ascochyta blight was established before a fungicide was applied. Some yield loss due to disease will occur.

Consider the following recommendations:

  • Apply fungicide if it has been close to 14 days since the last application.

Total Risk Value is > 80:

Your risk is high and ascochyta blight will impact your yield and seed quality. Consider the following recommendations:

  • Apply fungicide if crop is in the flowering to early pod stages and there is a potential for suitable yield.
  • Do not apply fungicide if disease is severe and there is little chance for economic return

Management of fungicide resistance: this is extremely important for ascochyta in chickpea due to the genetic diversity of the fungus, and the fact that isolates with resistance to strobilurin fungicides have been confirmed in Saskatchewan. If a pathogen develops resistance to one fungicide in the strobilurin group, it will be resistant to other fungicides in that group.

The following guidelines, adopted from the North American Fungicide Resistance Action Committee, are recommended to prevent the increase of fungicide-resistant fungi:

  • Do not use a fungicide that contains only a strobilurin active unless it is tank mixed with a non-strobilurin fungicide.
  • Rotate the use of a fungicide with a strobilurin product in the mix (or tank mixed) with a non- strobilurin product.
  • Do not use more than two applications per year of any fungicide containing a strobilurin on the same field.
  • Do not apply more than two applications of the same group in a single growing season (except for chlorothalonil, which can be applied three times).

Seed rot, seedling blight and root rot of chickpea are caused by a complex of pathogens including species of Pythium, Fusarium, Rhizoctonia and Botrytis. These pathogens are present in all Saskatchewan agricultural soils and can infect and kill individual seedlings from germination to the early flowering stage. Seed rots and seedling blights are most severe when soil is cool or saturated, and seedling emergence is delayed. Infected seed may fail to germinate. Infected seedlings will usually turn yellow, wilt and then die. Stems may be girdled and discoloured at or just below the soil surface and roots may be rotten, allowing the plants to be pulled easily from the soil. Kabuli chickpea is especially susceptible to rots due to its thin, zero-tannin seed coat.

Botrytis grey mold attacks chickpea, both at the seedling stage, and in advanced stages. Botrytis grey mold of seedlings may spread down a seed row, resulting in a series of yellow or dead seedlings. Botrytis grey mold is also favoured later in the growing season by dense canopies and moist conditions. Botrytis is usually most evident after flowering and is common on pods, resulting in shrunken, discoloured seed. The infected area is often covered by a dark grey, fuzzy, fungal growth. Botrytis pathogens can survive in the absence of host crops so rotation has limited effect on disease level. Fungicides are available for the control of late season development of botrytis grey mold on chickpea, but need to be applied prior to symptoms showing to be effective.

Sclerotinia white mold attacks chickpea grown in conditions of high rainfall, which produces dense crop canopies. This disease is more common in crop rotations that include other susceptible broadleaf crops such as canola, mustard, lentil, or pea. Symptoms usually occur in patches, typically in heavier crop areas. Infected plants are initially paler green and the diseased tissue may be covered by a white, cottony, fungal growth. The plant later becomes bleached in colour and the infected area will easily shred apart, revealing small black fungal resting structures. Sclerotinia becomes evident later in the growing season and if found, may have minimal impact on the crop. In most years it is not common through a lot of the chickpea growing area. Fungicides are available to control sclerotinia. However, they must be applied prior to the onset of symptoms.