166 STATE HORTICULTURAL SOCIETY. 



and the rapid growth of the fungus are required to start an outbreak 

 of the disease. The most important factor is excessive moisture in the 

 form of rain, which not only favors the production and germination 

 of the spores and the growth of the fungus, but renders tlie fruit soft 

 and watery, and therefore more susceptible to the disease. High tem- 

 peratures also favor the disease, although the fungus grows readily in 

 mild summer temperatures. Prolonged cloud}' weather Avith frequent 

 tight showers is more dangerous than a hard rain followed by clearing. 

 Warm, muggy weather, when the fruit is maturing, is often disastrous 

 to the crop. 



Insects, especially the curcnlio and certain plant bugs, play an im- 

 }>oi'tant part in the distribution of the spores and the infection of the 

 finiit. Although the fungiis under favorable conditions is apparently 

 able to pass readily through the unbroken skin of the fruit, it is greatly 

 aided by insect abrasions. In the process of feeding and egg laying, the 

 curcnlio punctures the skin of the fruit, opening the way for the fungiis 

 and in many cases perhaps actually inserting the spores. This insect 

 may render spraying for brown-rot partially ineffective by breaking the 

 sprayed skin of the fruit, thus exposing the flesh to attack. In the 

 treatment of the disease it is, therefore, important to combine an insecti- 

 cide with the fungicide so as to destroy the beetles. 



TREATMENT. 



Experiments conducted by the Bureau of Plant Industry during the 

 past four 3ears have shown conclusively that this disease can be con- 

 trolled by the use of self-boiled lime-sulphur mixture.^ 



PEACH SCAB. ECONOMIC IMPORTANCE OF THE DISEASE. 



Of the diseases affecting the fruit of the peach, scab is second only 

 to brown-rot in econontic importance; in fact, it is more destructive 

 than brown-rot in some of the mountain districts. It dwarfs the fruit 

 and causes premature dropping, thereby reducing the yield ; it ruptures 

 the skin, opening the way for brown-rot attacks; and it mars the ap- 

 pearance of the fruit, thus lowering the grade and reducing its market 

 value. The disease is common wherever peaches are grown east of the 

 Kocky Mountains, scarcely an orchard being entirely free from it. In 

 some cases, especially in a dry season, only a small percentage of the fruit 

 may become affected and with only a few small harmless spots, while in 

 other cases the entire crop may become so badly affected as to be un- 

 marketable. If the loss in the orchard and the reduction in market 

 value are both considered, it seemis evident that a loss of 10 per cent of 

 the total value of the peach crop in the eastern United States is caused 

 by i:>each scab. 



THE NATURE AND CAUSE OP THE DISEASE. 



The name commonly applied to this disease is "peach scab," but it 

 is also known as "black spot" and "freckles" and in some districts it is 

 often improperly called "mildew." It is caused by the fungus Clado- 

 sporium carpophilum Thiim., which grows in the skin of the fruit, pro- 



iCirculars 1 and 27 and Bulletin 174, Bureau of Plant Industry, U. S. Dept. of Agriculture. 



