August 2012. A question about Jatropha from Irian Jaya, Indonesia, showing leaf curling. It starts on the young leaves and spreads so that all the leaves are severely wilted. Could it be mite attack? Later, as a supplementary question, the writer said that he could see mites (photo: top, right) and asked if they transmitted viruses because some of the leaves are turning yellow with a mosaic pattern, and then brown. There are no whiteflies or aphids.

Members pointed out that leafcurl could be caused by insect pests such as thrips, aphids and mites, and also virus. Aphid infestation may give the leaf a more crinkly appearance in addition to curling. Your photographs suggest insect pests. With a hand lens you should be able to spot aphids or mites but probably not thrips as they move away swiftly. The short-term solution would be systemic insecticides for thrips and aphids, and sulphur for red mites. Preventive measures would be spray oil, windbreaks, or natural enemies if cost can be justified.

A number of other comments were received:

• It was thought unlikely that mites would be transmitting a virus, but there was always a possibility that they were causing a yellowing of the leaves
• A quick way to see if potential vectors were active in the field is to set up lightly greased blue and yellow sticky cards in the field. Thrips would be attracted more to the blue cards and aphids and other insects to the yellow. An inspection the next morning would help in making an estimate of vector activity to decide on appropriate action
• The symptoms look to be caused by a mite living in the growing point of the plant and therefore not visible on the mature leaf
• Leaf distortion that looks like a virus infection is typical of Tarsonemid mites (Phytonemusor Polyphagotarsonemus). The mites are very small and difficult to see without a microscope
• If it was aphid damage you would see them; thrips damage would leave some scarring or flecking on the foliage; and larger leaf inhabiting mites can be seen with the naked eye
• Control may be with a predatory mite if available (Amblysieus) or petroleum oil sprays or other acaricidal pesticide (abamectin, spiromefisin, spiridoclofen).