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Ascochyta blight symptoms on bean plant.

Dry Beans

Ascochyta Blight (Garbanzo Beans)

Pathogen: Ascochyta rabiei, Didymella rabiei

(Reviewed 8/07, updated 12/08)

In this Guideline:


SYMPTOMS AND SIGNS

Ascochyta blight is a serious disease of garbanzo beans. Symptoms develop on all aerial parts of the plant at any stage of growth.

On seedlings, brown lesions that develop at the base of the stem may lead to damping-off like symptoms.

During or after cool, rainy weather, foliar symptoms first appear on leaves as circular light brown lesions with no margins. As the lesions continue to develop small, black, raised spots (pycnidia) form in concentric circles within the lesions and are a good diagnostic characteristic of the disease.

Dark brown stem lesions weaken the stem, which often breaks. Lesions on pods are similar to those on leaves and result in poor seed set. Pod infection may also lead to discoloration and shrinkage of the seed. Developing beans can become infected and, if used for seed, can lead to early infections in the next crop. Overall, severe infections lead to general plant blight.

COMMENTS ON THE DISEASE

The fungus overwinters on infected garbanzo debris left in the field or in or on seed. During wet weather, spores are released from pycnidia and are splashed or carried in rain or irrigation water. (This is the asexual spore stage that has been identified as Ascochyta rabiei.) Once plants become infected, new spores are formed that spread to adjacent plants, creating expanding areas of diseased plants in fields. Symptoms develop 3 to 6 days after infection; moderate temperatures (68° to 77°F) and wet weather are optimum for severe disease.

Another type of fruiting body, pseudothecia, may develop when both compatible mating types of the fungus are present. Spores produced in pseudothecia are airborne and may play an important role in long-distance dispersal of the pathogen but are not important in local and short-term disease development. This is the sexual spore stage, which is identified as Didymella rabiei.

MANAGEMENT

The use of tolerant cultivars is one of the most effective and economical disease management practices. However, because more than one Ascochyta mating type has been identified, host plant resistance/tolerance to the disease is good for a limited number of growing seasons. Currently available public and private varieties with tolerance to most or all mating types identified in California include Sierra, Dylan, HB-14, Sutter, San Joaquin, and recent releases of the Airway Farms (AWF) series.

In susceptible varieties, cultural practices can be effective in managing this disease. Always use clean seed, rotate away from garbanzos, and thoroughly incorporate infested garbanzo residue. Crop rotation of 2 to 3 years will eliminate inoculum in the soil because the fungus won't survive in the absence of garbanzo host tissue. Wide row and plant spacing may increase ventilation between plants and reduce favorable conditions for plant infection.

Always plant seed that has been treated. Foliar applications of fungicides limit the rate of disease spread. Apply fungicides at first sign of disease and re-apply according to the label if rainy weather is forecasted. Thorough coverage of the plant canopy is important.

Common name Amount to Use** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental quality. Not all registered pesticides are listed. Always read label of product being used.
 
SEED TREATMENTS
A. THIABENDAZOLE
  (Mertect) 340-F 2.04 fl oz/100 lb seed    
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: Use allowed under a 24(c) registration.
 
FOLIAR APPLICATIONS
A. CHLOROTHALONIL
  (Bravo WeatherStik) 1.36-2 pt 12 14
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: A protectant. Apply at first sign of disease before rain or sprinkler irrigation.
 
B. PYRACLOSTROBIN
  (Headline) 6-9 fl oz 12 21
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Apply before or within 36 hours of a rain.
 
C. AZOXYSTROBIN
  (Quadris) 6-15.5 fl oz 4 14
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Apply before or within 36 hours of a rain.
 
D. BOSCALID
  (Endura) 8–11 oz 12 21
  MODE OF ACTION GROUP NAME (NUMBER1): Carboxamide (7)
  COMMENTS: Apply before or within 36 hours of a rain.
 
** Mix with sufficient water to obtain full coverage.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Diseases
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Abiotic Disorders:
A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:
S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):
R. L. Gilbertson, Plant Pathology, UC Davis

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