July 2012. Taro leaf spots sent from CARDI, Trinidad and Tobago for identification.

A member said that these relatively minor leaf spots of taro are not easy to diagnose from images, and there is a lot of confusion about them.

From a Pacific prospective, the photo shows symptoms of shot-hole caused by Phoma sp. Before the work of Wolfgang Gerlach in Samoa it was generally assumed that Phyllosticta was the cause. Wolfgang in his book Plant Diseases of Western Samoa describes Phoma colocasiae ined. Whether he published a taxonomic description I do not know.

Then there are the ghost spots, Cladosporium colocasiae and Neojohnstonia colocasiae which are impossible (by me at least) to differentiate in the field.

Another “spot” is Pseudocercospora colocasiae which causes a whitish leaf blotch. Again not easy to diagnose in the field. In the Pacific, this does not cause a shot hole symptom as far as I am aware.

Shot-hole in the Pacific is common in Vanuatu and also Fiji. In Fiji, it is common on some varieties especially in cooler times of the year. Damage can occasionally be severe, but usually only on older leaves. No one has reported any affects on yield, but no one has checked as far as I am aware. I doubt that it reduces corm yield though.

There is a fact sheet on these minor leaf spots, and you can find that at:

http://adder.cbit.uq.edu.au/project_files/Solomon%20Islands/Fact%20sheets/EXTENSION/

You’ll have to download Extension Fact Sheets 76-101c.pdf

Or if that is too big to download (it’s about 4 mb) go to Pest Fact Sheets on the Pestnet website (staging.pestnet.org); this will take you to the Extension fact sheets and you can see no. 94 Taro Leaf Spots (this is an unedited version).