In October 1939, Thung was appointed head of the Mycological Division of the Institute for Plant Diseases and Pests at Buitenzorg.

A position in which, according to his teacher and friend Quanjer, he could more effectively use his knowledge to benefit agriculture in the Dutch East Indies and the interests of science in general.

Not long after his appointment, however, international science ground to a halt with the outbreak of the Second World War.