PEACH SCAB. 13 



a series of cloudy days with frequent showers occurs about picking 

 time, half or even all of the crop may be destroyed by brown-rot. 

 Prolonged cloudy, drizzly weather, even though the precipitation 

 may not be great, is far more dangerous than a heavy rain followed by 

 clearing. Hot weather also favors the rapid growth of the fungus 

 and increases the danger of its destroying the crop. 



INFLUENCE OF INSECTS. 



The spores are undoubtedlv distributed broadcast by the wind, so 

 that they are in most cases ever present on the fruit ready to pro- 

 duce an outbreak of the disease when the conditions are favorable. 

 Although the fungus appears to be able to enter the peach through 

 the unbroken skin, entrance is more readily accomplished through 

 abrasions such as are made by insects and through cracks due to the 

 scab fungus. Sucking insects of the squash-bug family (Coreida?) have 

 been observed to puncture healthy and diseased fruits indiscrimi- 

 nately^ thus not only distributing the spores but probably inserting 

 them into the peach. But the curculio is by far the worst offender. 

 It breaks the skin of the peach and leaves a wound through which 

 the fungus readily gains entrance. Although the wound may appar- 

 ently heal before an outbreak of rot occurs, an exudation of gum often 

 keeps it open sufficiently to admit the fungus. The work of this 

 insect greatly reduces the efficiency of fungicides applied for the con- 

 trol of brown-rot. It punctures the fruit through the coating of 

 spray, possibly inserting brown-rot spores and certainly leaving an 

 opening for the fungus. In experiments conducted by the Bureau of 

 Plant Industry in cooperation with the Bureau of Entomology it was 

 found that 93 per cent of the brown-rot infections on sprayed fruit 

 had taken place through curculio punctures. It is evident, therefore, 

 that in order to secure the best results from spraying for brown-rot, 

 the curculio must also be controlled. 



PEACH SCAB. 

 CHARACTER OF THE DISEASE. 



Peach scab is a disease caused by the fungus Cladosporium carpo- 

 phUum Thum. It is also known as black-spot, and peach growers 

 often call it "freckles," which is an appropriate name, owing to the 

 freckled appearance the disease gives to the fruit. The spots are 

 dark brown or blackish, circular in outline, and about one-eighth of 

 an inch or less in diameter. They are often so numerous that one 

 side of the peach has a "smutty " or blackish appearance, cracks open, 

 and shrivels. (See PI. Ill, figs. 1 and 2.) 



o Scott and Fiake. Bulletin 31, Division of Entomology, U. S. Dept. of Agricul- 

 ture, p. 29. 

 174 



