Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Bean (Ascochyta) leaf spot (319)

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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.

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