May 2004. Potato with leaf curl from the highlands of Papua New Guinea. The leaves of affected plants show signs of veinal chlorosis, leaf puckering, reduced leaf size, leaf tip die back or burning, shorter stem internodes producing a rossette, as seen in the picture. The potato variety is cv. Granula imported in bulk (5 tonnes) from Victoria, Australia and planted straight away. The symptoms were observed commencing 2 weeks after planting, and severe in the fourth week after planting. At 6 weeks most of the plants grew out of the symptom and continued growing normally. It was unclear whether it is due to physiology of the variety, influence of the environment or caused by a biotic (virus) agent.

There were several suggestions:

Mites

Mites are not normally seen on the distorted leaves as they are in the growing point and the feeding causes distortion and cupping of the leaves as they enlarge. Try whatever miticides are available. The distorted leaves will stay distorted, but that new growth should be healthy.

Insects – jassids

These are poplyphagous, attacking peanuts, aibika (Abelmoschus esculentum), beans, etc. The insects are green and fast moving, living on the underside of the leaves. The symptoms disappear once the affected plants are sprayed with permenthrin at 0.5litres/ha. Also, if left unsprayed, the symptoms in peanuts disappear in 5-7weeks. However, with aibika the symptoms persist and plants may be killed.

Soil toxicity

Many of the highland soils are acid pH 4.5-5.0 and research by AFTSEMU and EYL (?World Bank project in Enga) showed very high levels of P fixation. Could the plants be showing a nutrient problem from which they recover as roots develop. What fertilizers are being applied; and is there additional P?

Also, how are the farmers applying fertilizer. There was a situation in the early 90’s where Enga and WHP farmers where having trouble with burns, cupped and strange looking leaves. It turned out that a major supplier started importing fertilizer from a different source and farmers had problems if they applied this fertilizer in direct contact with the seed, when planting in rows, or not mixing the fertilizer well with soil when planting in individual holes. The potato seed production stations who were banding fertilizer at distance from the seed had no problems. It may be worthwhile to dig up a few plants and have a few farmers demonstrate their planting techniques.