SEPTORIA CANKER OF INTRODUCED AND NATIVE HYBRID POPLARS

Abstract

Studies have shown that Septoria musiva Peck, a North American fungus which occurs commonly as a leaf-spotting parasite on native poplars, produces cankers, in addition to leaf injury, on certain introduced poplars (Populus Rasumowskyana Schneid., P. Petrowskyana Schneid., and P. berolinensis Dipp.), and the native hybrids, Northwest and Saskatchewan poplar.Field observations and inoculation experiments demonstrated that most of the inoculum for spring infection arises from ascospores of a Mycosphaerella stage, and that the fungus enters the stems through mechanical wounds uninjured lenticels, leaf petioles, or stipules. Incipient cankers occur in the bark of the current year's wood, soon girdling leading and side shoots. They later spread from lateral branches into the main stem, developing into perennial cankers which ultimately girdle and kill the trees.