DISEASES OF CULTIVATED PLANTS 457 



diseased areas may run together forming a large irregular dead patch 

 of tissue. Luckily this disease is more amenable to treatment than 

 the Rust. In fact if the orchard is thoroughly treated with Bordeaux 

 Mixture for the Scab there will likely be little or no injury from the 

 Brown Spot. If untreated however, the disease may cause a serious 

 loss as it works early in the season often causing the foliage to fall in 

 July. It may and usually does appear again in August or September 

 and when this occurs the foliage falls early, before the fruits are 

 grown and colored. Injury at this stage produces loss of flavor, lack 

 of color, and improper maturity and probably a poorer-keeping 

 product. (W. Va. E. S. B. 66.) 



Apple Mildew. Podosphaera oxyacanthae. It attacks water 

 sprouts, young twigs and leaves. It is most frequently found on nur- 

 sery stock. It forms a powdery-whitish surface which later becomes 

 a dirty white. When abundant on the leaves it causes them to roll 

 up and occasionally to fall off. The disease can be controlled by the 

 use of either Bordeaux mixture or potassium sulphide. (Wash. E. S. 

 B. 70.) 



Bitter-Rot. This is one of our most destructive diseases. It 

 most frequently appears on the fruit usually during the months of 

 July and August ; still it has been observed as early as June 25th. 

 The time of its first appearance varies with climatic conditions of the 

 season. The first spots often develop on fruit when it is about half 

 grown, and the disease usually continues to spread with increasing 

 severity until the crop is harvested. Warm, sultry weather follow- 

 ing a rain forms an ideal condition for the development of this or- 

 ganism. In cool, dry summers the disease develops sparingly. A 

 few hot, wet days in August may bring on a very sudden and de- 

 structive attack. Nights with very heavy dews alternating with hot 

 days may also cause the rapid development of this organism and 

 often cause the complete destruction of a promising crop in a few 

 days. Cold weather soon checks its development. When the fungus 

 attacks the fruit small light-brown spots appear, which increase rap- 

 idly in size. These spots soon take on a dark brown color, and their 

 borders are usually circular in form. While quite small they become 

 sunken, the tissue being soft and bitter to the taste. Small black 

 dots appear usually at regular intervals beneath the epidermis on the 

 sunken spots. These black bodies increase in size, and soon give off 

 a large number of spores. These spores often exude in the form of 

 minute pink threads which are quite sticky when moist. As the dis- 

 ease advances in the tissue of the apple, these black bodies are often 

 arranged in form of rings. If the weather is unusually favorable for 

 the growth of such organism, as high as nine or more of these rings 

 may form in rapid succession. Unfavorable weather retards the 

 growth of the fungus and tends to produce an irregular development 

 of these black postular rings. The pinkish appearance of the dis- 

 eased area on the apple is due to the spores oozing out of the^e black 

 bodies and forming in large masses on the skin of the infected areas. 

 The size of the diseased areas usually increases rapidly, and two or 

 more separate infections may join, but the apple seldom decays en- 



