Late Blight

Stem canker results from early season infections from Rhizoctonia solani on potato crops. The fungus attacks emerging stems causing characteristic browning /blackening symptoms on stems inside the moulds. Often results in delayed emergence and in severe cases can kill stems resulting in gappy crops. Infected plants also have reduced yields, misshapen tubers, uneven tuber sizing and reduced internal tuber quality.

Causal organism – Rhizoctonia solani. Black scurf manifests itself as raised black encrustations on potato tubers. These are the resting bodies (sclerotia) of fungus. Being unsightly, Black scurf is very visible once potatoes are washed and requires grading out of high value pre-pack market lines.

Potato tuber moth (Phthorimaea operculella) is an issue for potato growers throughout New Zealand. The larvae can mine leaves but the major challenge is in the dry season when the soil cracks and adults can directly access and lay eggs on the tubers. The larvae then burrow into the tubers rendering them unmarketable and causing rots in storage.