This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Amongst these are Mildew, Leaf Spot, and Sleepy Disease. The Mildew appears in the form of a whitish efflorescence on the leaves, but does not cause much injury. It may be checked by syringing with water in which a little camphor has been dissolved for a few hours. An ounce or two of camphor should be placed in a muslin bag and sunk in the water tank for the purpose.
The Cucumber and Melon Leaf Spot is caused by a fungus called Cercospora Melonis. It attacks the leaves first of all in the form of small brownish spots, which rapidly develop into confluent patches, and ultimately destroy the green assimilating tissue of the entire leaf. This disease has been brought about by the "express" or steaming method of growing Cucumbers under conditions quite unnatural. Too much heat, too much water, too much manure, and too little fresh air - those are the causes of Leaf Spot, and, until they are removed, any amount of fungicides will have no effect. Solutions of sulphide of potassium or liver of sulphur (1 oz. to 3 gall, of water), carbolic, cyllin, lysol, and other disinfectants have been applied in the vain hope that they will prevent the disease, but they are quite unavailing under the bad conditions mentioned.
Sleepy Disease causes the leaves to flag or wilt suddenly without apparent cause. It is best to take affected plants up and burn them. [J. W].