22 manual of tree diseases 



Drought-Injxjey and Sun-Scorch 



Caused by high, temperatures and dry soils 



In midsummer the foliage of many kinds of trees often ap- 

 pears scorched. Pines and maples are commonly affected. The 

 leaves of one side or of the entire tree may wither and turn 

 brown. In general, this type of summer injury is similar to 

 winter-drying (see page 18). The effects are the same and the 

 causes similar. In winter-drying of conifers, a greater amount 

 of water is lost than can be replaced because the ground-water 

 is frozen. In the case of drought-injury and sun-scorch, water 

 is lost from the leaves in quantities that cannot be replaced 

 because of many conditions, such as : diseased or injured roots, 

 a low water-table due to continued drought, or naturally dry 

 and sandy soil. The injury usually occurs on the exposed 

 side of the tree and commonly follows periods of hot dry winds. 

 The sun-scorch of maple leaves has been found to follow imme- 

 diately after an hour's exposure to high winds on hot days. 



In the case of conifers, the needles of the affected parts of the 

 tree turn uniformly brown. With deciduous trees, large or small 

 spots may be killed, leaving the remainder of the blade healthy 

 and green. Usually the edge of the leaf, or the portion midway 

 between the main veins, suffers first. Then if the drought con- 

 ditions continue, the entire leaf may be killed and turn brown. 

 The bronzed appearance of maple leaves commonly seen is 

 typical of sun-scorch injury. Although, as stated above, sun- 

 scorch following drought conditions or exposure to hot drying 

 winds is usually found to be due to damaged root systems or 

 dry soil,^ it sometimes happens that trees not so predisposed 

 suffer merely from the effects of rapid transpiration. 



Reference 



Stone, G. E. Sun scorch and bronzing of leaves. In Shade treeS, 

 characteristics, adaptation, diseases and care. Massachusetts 

 Agr. Exp. Sta. Bui. 170 : 210-212. 1916. 



