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 
