This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
This disease of the leaves occurs in many parts of the country and is often confused with early blight," says B. T. Galloway in "Farmers' Bulletin No. 91." "The tips and edges of the leaves turn brown and these discolored areas soon become hard and brittle.
The burning or scalding may occur at any time and as a rule is the result of unfavorable conditions surrounding the plant. Long-continued, cloudy and damp weather followed by several hot and bright days is very apt to result in the burning of the foliage. This is especially the case on soils carrying a comparatively small percentage of moisture. When the weather is cloudy and damp the tissues of the potato become gorged with water and this has a tendency to weaken them. If the sun appears bright and hot when the leaves are in this condition there is a rapid evaporation of the moisture stored up in their cells. The evaporation may be faster than the supply furnished by the roots, and if this continues for any length of time the weaker and more tender parts first collapse, then die, and finally turn brown and dry up. Tip burn may also occur as a result of protracted dry weather.
Little of a specific nature can be said on the treatment of this trouble. Numerous factors are involved in the matter, so that only general statements are possible. Every effort should be made to keep the plants in good growing condition, for if they become checked through lack of proper food or cultivation, or both, they are more apt to burn. It is a fact that where the Bordeaux mixture is used for other diseases burn is less apt to occur, and this furnishes another instance of the remarkable properties of the fungicide. Briefly, therefore, the plants should be kept as vigorous as possible by good cultivation, plenty of available food, and the application of Bordeaux mixture as recommended for early blight.
In many sections where Paris green in water is applied to potatoes, injuries are produced which cannot be distinguished from early blight by an ordinary examination. It frequently happens, therefore, that farmers are led to believe that their potatoes are affected with early blight and other diseases when the trouble has been brought on by themselves through the improper use of Paris green. Injuries resulting from the use of this substance are very apt to occur where flea beetles have eaten the foliage. The arsenic attacks the tissues at such points, and as a result more or less circular brown spots are produced, having for their centres the holes eaten out by the flea beetles. By combining the Paris green with Bordeaux mixture, as already described, these injuries may be wholly avoided. "The cost of the work of spraying, as described here will depend to a considerable extent upon the kind of machinery used and the price paid for labor. With suitable apparatus, and labor at $1.50 per day, potatoes may be sprayed six times for about $6 per acre. This estimate is based upon experiments extending over several years, and includes the cost of chemicals as well as labor. The cost of treating scab is mainly in the labor involved in dipping and drying the seed, and seldom exceeds 15 cents per acre. Much attention has been given to the effects of Bordeaux mixture on the growth and yield of potatoes aside from its value in keeping parasitic foes in check. It has been shown conclusively that it pays to apply this preparation if for no other purpose than to induce a more vigorous growth. Three or four applications of the mixture have in many cases increased the yield of potatoes 50 per cent., so that no matter where the crop is grown, or whether diseases are present or not, the writer feels warranted in recommending the application of the mixture, on the ground that its use will yield a handsome return."