DISEASES OF CULTIVATED PLANTS 477 



brown-rot fungus. Through handling by pickers and packers some 

 fruit in every package may become contaminated with spores from 

 a few diseased fruits in the orchard. Enough moisture usually de- 

 velops in the car to germinate the spores, and if the refrigeration is 

 poor the fruit is likely to go down in partial or total decay before 

 reaching the consumer. 



The fungus also attacks the blossoms and extends from these 

 into the fruit-bearing twigs, often girdling them. In a wet spring 

 the fruit crop may thus be materially reduced, although this form of 

 attack is only occasionally serious. In like manner the fungus may 

 extend from diseased fruits into the twigs. Following an outbreak 

 of brown-rot on the fruit, these twig infections may become so severe 

 as to give the trees a blighted appearance. 



The affected fruits largely drop to the ground, although many 

 of them hang on the trees for months. They become dried and 

 shriveled, and at this stage are known as brown-rot mummies. The 

 fungus passes the winter in these mummies, which form the chief 

 source of infection for the new fruit crop. When moistened by 

 spring rains, the mummified fruits on the trees and on the ground 

 become covered with fruiting tufts of the fungus, producing count- 

 less numbers of spores. 



After 18 months, or at the end of the second winter, about the 

 time peach trees are in bloom, there arises from the mummies on the 

 ground, partly or entirely covered with soil, fruiting bodies repre- 

 senting the perfect stage of the fungus. These are dark-brown 

 somewhat bell-shaped disks, resembling toadstools. In them are 

 produced an abundance of ascospores, which rise in the air and are 

 wafted by the wind. These, as well as the summer spores (conidia),. 

 serve to infect the blossoms and young fruits. The propagation of 

 the fungus being thus so abundantly provided for, it is not surprising 

 that a crop of fruit may be destroyed without much warning. 



In sections where the brown-rot is prevalent the spores are 

 practically omnipresent, and only favorable conditions for their 

 germination 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 the fruit soft and watery, and therefore more susceptible to 

 the disease. High temperatures also favor the disease, although the 

 fungus grows readily in mild summer temperatures. Prolonged 

 cloudy weather with frequent light 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 curculio and certain plant bugs, play an 

 important part in the distribution of the spores and the infection of 

 the fruit. Although the fungus under favorable conditions is ap- 

 parently 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 curculio punctures the skin of the fruit, opening the 

 way for the fungus ana in many cases perhaps actually inserting 



