A B C D E F G HIJ K L M N O PQR S TUV WXY Z

Pacific Pests & Pathogens - Mini Fact Sheet Edition

Bean (Ascochyta) leaf spot (319)

Photo 1. Leaf spot of Ascochyta spot, Boeremia exigua on tobacco.

Photo 2. Ascochyta spots on bean leaves, Boeremia exigua. The spot on the left shows concentric rings and a dark margin.

Photo 3. Leaf spots of Ascochyta spot, Boeremia exigua, on common bean. The leaf on the right shows spots with ring patterns.

Photo 4. A spore-containing sac (pycnidia) of Ascochyta spot, Boeremia exigua.

Photo 5. Ascochyta spot, Boeremia exigua, on bean pods.

Summary

Worldwide distribution. On wide range of plants, especially beans and other food legumes; also on citrus and capsicum. Minor fungal disease,
Weak pathogen, requiring wounds from insects or weather to enter leaves and pods.
Grey to brown spots on leaves, 6-12 mm diameter, with concentric circles; sometimes falling out. Darker spots on pods. Tiny, black, spore-containing sacs on spots, seen with naked eye.
Spread occurs in wet weather; spores ooze from sacs and blown in wind and rain. Possibly, seed-borne.
Cultural control: certified seed or treat seed in hot water (50°C for 25-30 mins); remove volunteers; select well-drained soils; avoid damage by strong winds, and during cultural operations; weed; after harvest, handle beans carefully; collect and burn crop debris; crop rotation.
Chemical control: probably not needed as wound pathogen; if required, use pyrethrum, or synthetic pyrethoids.

Common Name

Ascochyta spot.

Scientific Name

Boeremia exigua; previously known as Ascochyta phaseolorum, and Phoma exigua, and many other names. The name now given to the fungus is Boeremia exigua var. exigua.

AUTHORS Grahame Jackson & Eric McKenzie
Information (and Photos 2&5) Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing; and from CABI (2016) Boeremia exigua var. exigua (leaf spot) Crop Protection Compendium. (www.cabi.org/cpc). Photo 1 R.J. Reynolds Tobacco Company Slide Set R.J. Reynolds Tobacco Company, Bugwood.org. Photo 3 Howard F. Schwartz Colardo State University, Bugwood.org. Photo 4 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Boeremia exigua PaDIL - (http://www.padil.gov.au).

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

This mini fact sheet is a part of the app Pacific Pests and Pathogens

The mobile application is available from the Google Play Store and Apple iTunes.