Gummy stem blight

 Mycosphaerella melonis (Didymella bryoniae), causes lesions on leaves and stems, and less frequently on the fruits. This fungus attacks all cucurbits. Seedlings die rapidly if hypococtyls or cotyledons are infected. In older plants lesions produce a characteristic red or brown exudate at the crown of the plant and along the vines. Black spores may be seen around the infected tissue. Initial leaf symptoms are irregular circular dark spots which may be surrounded by a yellow halo, and later dry up and crack. Infection starts from the leaf margins and proceeds inwards resulting in a typical leaf blight. Affected fruit have small water soaked circular brown spots which have a greasy appearance. Small black spores may also develop in these lesions. The pathogen enters the plant through wounds caused by insects, wind, sand or machinery. The organism survives on crop debris and cucurbit seeds for a period of two years. High disease pressure can be expected in the field and in the greenhouse under wet and cool conditions.

Controls include soil sterilization and proper sanitation in the greenhouse,

weekly fungicide applications, rotations, and a choice of drip instead of 

sprinkler irrigation. No resistance exists on current commercial cultivars.