STATE POMOl.OGICAL SOCIETY. 51 



fruit crops. They are plants of a much larger growth, yet so small 

 as to be visible to the naked eye only when seen in large masses, as 

 the meal}' or downy growth on the leaves of the grape vine, the 

 yellow spots on the grass leaves and the brown spots on the leaves 

 of the pear, apple and strawberry. 



The germs or spores from which these plants originate are very 

 minute and are easily carried about in the air but are generally hun- 

 dredths of times larger than the germs of the true blights. These 

 germs coming in contact with the leaf surface of the host-plant 

 when there is rain or dew upon it, germinate and throw their 

 roots down through the stoma feeding upon the juices. They 

 grow only under conditions of moisture and heat, however, and 

 in dry seasons very little injury is caused by them. 



Like the blights for complete and rapid development, this class of 

 plants are more or less dependent upon the condition of the host- 

 plant. If the foliage is healthy and vigorous, the juices do not 

 offer that condition of food under which the parasite can exist, and 

 while the temperature and moisture of the season may be such as to 

 cause an unhealthy condition of the tree, thus leading to an attack, 

 much may be done by proper manuring, cultivation, etc., to over- 

 come the injur}'. 



Leaf Blights. The leaf blights are abundant on the pear, plum, 

 cherry, and in some cases on the apple, and our strawberry crop is 

 often seriously injured in the same way. The pear leaf blight comes 

 on during hot, moist weather in July, often in severe cases, caus- 

 ing all the leaves to drop, and the tree remains bare until a new 

 set is formed. Some varieties are more liable to injury than others, 

 and it is especially injurious to young seedlings in the nursery 

 before they are budded. In the nursery when the first spots 

 appear on the leaves, we start the cultivator to loosen and lighten 

 the soil, and if there is an indication of a want of plant food in the 

 soil, some very soluble fertilizer is applied to give the seedlings a 

 start into renewed growth. To prevent leaf blight on large trees 

 in the orchard is a more difficult thing to do. If the land is well 

 underdraiued, if manures are applied only in the fall in sufficient 

 quantities, and if the trees are not injured by over-bearing, by 

 insects or by mutilation with the plow or saw, very little injury 

 need be feared from leaf blight. Manures containing an excess of 

 potash and phosphoric acid are especially valuable for a healthy 

 growth of all fruit trees. Leaf blight upon the apple, cherry, plum 



