TREE DISEASES AND TREATMENT 181 



leaves themselves. On the leaves these attacks produce 

 spots or holes, or cause the foliage to wither as from frost. 

 This disease is especially prevalent on the Sycamore, 

 where it follows the veins of the leaf and then spreads, 

 causing the entire surface to turn brown. It often kills 

 the shoots of young and tender growth, causing them to 

 appear as if killed by frost, and may even kill trees. To 

 control this disease, dead or diseased branches and twigs 

 should be cut away and burned. Either Bordeaux mixture 

 or lime-sulphur should be applied by spraying during the 

 dormant season. Soon after the buds have opened, 

 affected trees should be sprayed with Bordeaux mixture, 

 and this spraying should be done a second and a third 

 time at ten day intervals thereafter. 



Powdery mildew is not serious, except to very young 

 trees and nursery stock. This disease spreads over the 

 surface of the leaves, forming a delicate white web resemb- 

 ling dust. It appears on the Oak, Birch, Maple, Poplar 

 and other trees. It may be removed by application of a 

 spray of one pound of potassium sulphide dissolved in 

 fifty gallons of water. Either Bordeaux mixture or diluted 

 copper sulphate also makes an effective spray, if applied 

 two or three times in July and August. 



Leaf curl appears on Oaks, giving the leaves a blistered 

 appearance. It should not be allowed to progress 

 unchecked. Fallen leaves should be burned, and the trees 

 should be sprayed during the winter with either copper 

 sulphate or lime-sulphur. 



Rust is a fungus which in various forms attacks many 

 kinds of trees, covering the leaves with brown and yellow 

 spore-masses, sometimes causing the leaves to become 

 ragged and unsightly. It attacks such trees as the Linden, 

 Poplar, Ash, and other broad-leaved trees, and also many 

 Conifers. On the Red Cedar it produces the reddish 



