Pacific Pests & Pathogens - Mini Fact Sheet Edition

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Maize southern leaf blight (080)

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Photo 1. Light tan, rectangular leaf spots, mostly on the lower leaves caused by southern leaf blight, Cochliobolus heterostrophus.

Photo 2. Spots on maize leaf, expanding and joining together, caused by southern leaf blight, Cochliobolus heterostrophus.

Summary

• Worldwide distribution. In tropics and sub-tropics. On sorghum and grasses. Occasional outbreaks have been serious. 
• Spots merge and cause leaves to dry and die. Spores on undersides of leaves spread in wind and rain splash.
• The blight survives in debris, and on “volunteers”.
• In the 1970s, in the US and elsewhere, a strain of the fungus (Race T), caused an epidemic, and resulted in ear rot, ear drop and lodging, and a large loss of yield. Race O is the common strain in the tropics and causes minor crop loss.
• Cultural control: resistant varieties; remove volunteers; provide mineral fertilizers or manures; wide spacing to reduce humidity; collect trash at harvest, compost or feed to livestock; plough-in remains; crop rotation.
• Chemical control: only use if resistant varieties are not available (main control method); use chlorothalonil or mancozeb. Apply when spots first appear.

Common Name

Southern leaf blight, southern corn leaf blight, southern leaf spot, maydis leaf blight

Scientific Name

Cochliobolus heterostrophus; this is the name for the sexual stage; the asexual stage is known as Bipolaris maydis (previously it was Drechslera maydis and before that Helminthosporium maydis). There are different races.

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