HEALTH AND DISEASE ^57 



disastrous attacks of disease. Among the fruits may be mentioned fire blight 

 which caused "one of the greatest industries of the San Joaquin valley 

 to vanish like a dream" when 500,000 pear trees were killed by the disease 

 within a few years. In the rich fruit section of New York State a new virus 

 disease of peaches has broken out in epiphytotic form, promising to be 

 even more destructive than any of the other twelve or more virus diseases 

 of this tree. In the tropics banana plantations cannot be permanent. In- 

 variably they become infested with the "Panama disease" after a few years. 



Among vegetables, the ravages of the potato blight are seconded by 

 those of watermelon wilt, at first welcomed as nature's way to maintain 

 price levels by restricting production, but soon wiping out the melon 

 industry in important sections of Florida, Iowa, and California. 



And in field crops the story is the same. Flax has always been a pioneer 

 crop, moving on to virgin areas and leaving behind a trail of "flax-sick" 

 soil, infested with the flax wilt fungus, soil upon which susceptible flax can- 

 not again be grown for many years. Texas root rot has rendered great 

 areas of the Southwest unsuitable for culture of cotton, alfalfa, and many 

 other crops. The disease causes a loss in Texas of 300,000 bales of cotton 

 a year, and in addition, attacks more than 2,000 other species of plants, 

 aggregating a total loss from this disease, in the seven states affected, which 

 reached $150,000,000 in 1947. And finally, no account of epiphytotics in 

 field crops can omit mention of the cereal rusts. Stem rust is always with 

 us, and now and then, when the weather is suitable, it rages northward 

 from the Great Plains to Canada leaving in its wake millions of acres of 

 wasted grain. These epiphytotics are coming more and more frequently. 

 There have been three in the past five years. That of 1935 destroyed a 

 quarter of the national wheat crop, a total of 160,000,000 bushels, and in 

 North Dakota and Minnesota 60 per cent, of the wheat crop was sacrificed 

 to stem rust. 



This is the spectacular side of plant disease, the great epiphytotics that 

 are so often followed by privation, suffering, loss of homes and farms, even 

 famine, migration, or abandonment of farming. 



How many farmers realize that a small percentage of loss in the field 

 represents a much larger loss, perhaps all, of the profit. To be specific, take 

 the case of a farmer with a quarter-section in wheat, and assume that under 

 disease-free conditions his average yield is a conservative 25 bushels to the 

 acre, or a total of 4,000 bushels. The harvest return is divided into two 

 elements, part, usually most of it, must be paid out to cover all the costs of 

 production of that crop, the remainder is the farmer's profit, and may be 

 applied to maintaining and improving his standard of living and of farming. 

 Under normal circumstances the 4,000 bushels would be used somewhat 

 after this fashion: use of the land, 40 per cent; seed, 3 per cent; labor, 12 per 

 cent; machinery and maintenance, 20 per cent; insurance, 5 per cent; leav- 

 ing a profit of 20 per cent, based on disease-free conditions. The loss from 



