Wahl started to teach at The Hebrew University of Jerusalem's Faculty of Agriculture in Rehovot, where he developed Plant Pathology as one of the important disciplines. He later moved to Tel Aviv University where he established the Institute for Cereal Crops Improvement. He looked at  host-pathogen interaction in its wider ecological concept, including the weed progenitors of the cultivated crop species.  Wahl's research on the cultivated and wild progenitors of barley, oats and wheat, and on their pathogens led not only to new sources of resistance but also to a better understanding of the wild ecosystem.  Prof. Wahl and his students found many new sources of disease resistance, which they characterized and made available freely to crop improvement teams worldwide. Wahl was honored with the prestigious Rothschild Prize (1964) and the Harvey Prize (1978), and with the Bruno Kreisky Award for Service to Humanity (Vienna, Austria, 1985). The President of Israel presented him in 1992 with the prestigious Israel Prize in the Life Sciences for his work in pathology and mycology.