DISEASES OF CULTIVATED PLANTS 517 



sulphur solution, it is not necessary to bring the insecticide in con- 

 tact with the mites. Observations by means of the microscope show 

 that these liquids do not have to come into actual contact with the 

 mites to prove effective, the fumes being sufficient. While conduct- 

 ing experiments in 1910 the effect of lime-sulphur on rust mites 

 came under observation incidentally. At the end of two and one- 

 half hours the effect on the rust mites could be made out by means 

 of a hand lens. In four hours' time the little pests had all collapsed, 

 some of them not having been touched by the insecticide. Some 

 fruits on the same tree had not been touched by the solution. On 

 these the mites were not destroyed. 



Use flowers of sulphur, or a mixture of equal parts air-slacked 

 lime and sulphur sifted together through a flour sifter. Apply by 

 means of an air gun. This is a simple and cheap remedy, but of 

 varying effectiveness. Soda-sulphur solution, or lime-sulphur solu- 

 tion one quart to fifty gallons of water is usually effective. At the 

 rate of one gallon to thirty of water these insecticides are likely to 

 cause chemical scalding. 



Melanose. This is a disease of the fruit, leaves and young 

 stems. The markings produced on these different organs are about 

 the same. The markings on the fruit are superficial and never ex- 

 tend into the rind. Unless they are very plentiful, they do not 

 affect the development of the fruit. Their presence causes the fruit 

 to be classed as a russet, thus affecting its market value. 



The markings caused by the disease are small brown spots, 

 which are scattered like pepper over the skin of the affected part. 

 They are circular to irregular in outline, and vary in size from mere 

 points to spots one-sixteenth of an inch in diameter. They are wax- 

 like in appearance, and resemble small drops of melted sugar burned 

 to a reddish-brown color. They are raised and cap-like, and are 

 never conical. Frequently where the markings are plentiful, they 

 will grow together, forming solid patches of irregular outline. These 

 patches will crack in lines like dried mud. 



Some of the markings may be arranged in lines forming circles 

 or parts of circles. The borders of the markings that make up these 

 lines are usually peeled away. This circular arrangement of the 

 markings is characteristic of melanose. 



Again, the markings on the fruit as a whole are sometimes so 

 arranged as to resemble the tear-streaking that is due to the wither- 

 tip fungus. This occurs where a dead twig over-hangs the fruit, so 

 that the drip from the twig falls upon it and runs down its side. 

 The melanose streaking is easily recognized by the character of the 

 markings in the streak. Fruit affected by melanose may also be 

 affected by other diseases that mark the epidermis. The mixture of 

 the markings due to the different causes often gives a peculiar ap- 

 pearance to the fruit, making it difficult to recognize the diseases. 



Melanose starts its development in the spring after the warm 

 weather has well begun. Periods of cold will delay its development. 

 It first shows as mere sunken points, that increase in size and become 

 raised as the fruit develops. Owing to its early stages being so in- 



