This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This disease is prevalent wherever the Strawberry is cultivated, and is always in evidence, although it is only now and again that it assumes the proportions of an epidemic. As a rule it appears rather late in the season, after the crop has been picked, where its presence is usually ignored. This is unfortunate, as the mass of spores produced are quite likely to set up the disease quite early in the following season. The leaves only are attacked, and the symptoms are unmistakable. Small reddish patches first appear, almost equally well marked on both surfaces of the leaf. These patches continue to increase in size, usually retaining a more or less circular outline, and often run into each other. By degrees the centre of each patch becomes greyish, or often almost white, and is bounded by a reddish border, which is often quite bright in colour during the autumn. The pale central portion soon becomes covered with minute tufts of the summer fruit of the fungus, once known as Ramularia tulasnei and supposed to be the only form of fungus connected with the disease. The dispersal of the summer spores causes the disease to spread rapidly during dull, damp weather. Later in the season the winter form of fruit appears on the pale patches. These dead patches do not fall away from the leaf, but persist until the leaf actually decays, when the spores are liberated.
When the disease appears early in the season, the crop of fruit is much reduced both in quantity and in quality, The plants are also weakened for the following season.
The most certain way of dealing with Strawberry beds that have been diseased is to mow off the leaves soon after the fruit has been picked, and, when the mown leaves are fairly dry, to cover the whole bed with a sprinkling of straw, litter, or other convenient material that will burn well, and set it on fire. By this method not only are all diseased, spore-carrying leaves destroyed, but also dead fragments of leaves and spores lying on the ground. The destruction of many injurious insects is also included.
During the spring following the burning, the plants should be sprayed with sulphide of potassium, commencing when the leaves are quite young. Spraying should be continued at intervals until the blossom begins to open. If this procedure is followed the disease can be eradicated.