Stem blight is just blight

UK - March 12, 2004

Stem blight is the same organism that causes foliar and tuber blight but in a different place on the plant and so needs the same approach for effective control, according to Nick Gooch of Dow AgroSciences, who market the fungicide Electis* (zoxium + mancozeb).

“Although it was once thought of as a different disease, stem blight is caused by the same pathogen, Phytophthora infestans, which causes foliar blight and tuber blight. The stem lesions can appear before or after foliar infections and there are a number of theories to explain its origins. Some think that stem blight moves upwards from infected seed tubers, when small pieces of detached fungal hyphae grow up inside the developing stem from the tuber and then produce lesions randomly in the stem. Deep-seated infections are not easily controlled. When these lesions sporulate, Electis will prevent the production of viable sporangia and zoospores, by inhibiting cell division,” advises Nick.

Alternatively, others think that stem blight arises from foliar lesions higher up the plant. Spores from these leaf lesions land in the potato leaf axils, germinate and then penetrate the stem. In this instance, a good covering of an early protectant fungicide such as Electis before spore germination will give the protection that is needed. The spores may be oospores from a source external to the plant, sporangia or zoospores rain-splashed from the soil” concludes Nick.