12 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



with scorch may lose many leaves during late summer; usually 

 they do not die. Trees in low vigor may be aided in overcoming 

 scorch by being fed and watered. Sometimes it may be advisable 

 to remove interfering and weak branches from a tree and thereby 

 reduce the total foliage load that must be supported by the root 

 system. 



Chlorosis. — Trees suffering from lack of available nutrients 

 such as iron, magnesium, manganese, boron, zinc, and nitrogen 

 usually show abnormal color of leaves or abnormal types of 

 growth. Probably the most common type of deficiency disease is 

 chlorosis, caused by the nonavailability of iron. Chlorosis fre- 

 quently occurs in oak, especially pin oak, and sweetgum, and it 

 occasionally occurs in other deciduous trees and in evergreens, 

 especially pines. In pin oak and other deciduous trees, it de- 

 velops as yellowing of tissues between the veins of leaves (Fig. 

 14). In a severe case, the leaves curl and turn brown along the 

 margins, or they develop angular brown spots between the veins. 

 Later the leaves and twigs may die; the affected tree may be 

 stunted in growth or it may die. Chlorosis of pines usually de- 

 velops as an overall yellowing of needles. 



Chlorosis may develop because of unfavorable conditions 

 for the utilization of iron in the tree or in the soil. Under alka- 

 line conditions, or at a pH above 6.7, iron changes to insoluble 

 forms. Iron is most readily available at a pH range of 5 to 6.5. 

 Deficiency of available iron is aggravated by low temperature 

 and high moisture, by relatively large amounts of copper, manga- 

 nese, and zinc, by insufficient potassium, and by excessive ap- 

 plication of phosphorus fertilizer. Frequently trees recover from 

 chlorosis when they are supplied with available iron. The iron 

 may be sprayed on the chlorotic leaves, introduced into the trunk, 

 or added to the soil. Spraying the foliage thoroughly usually 

 corrects chlorosis of the leaves that are treated, but it is not 

 likely to benefit leaves produced after the iron has been applied. 

 A spray composed of 5 pounds of iron sulfate (ferrous sulfate) 

 and 2 pounds of soybean flour in 100 gallons of water is most 

 effective when applied in late spring or early summer, during the 

 time the leaves are increasing in size. Table 2 (end of circular) 

 gives equivalent measurements for small quantities of spray. 



Introducing iron into the trunk of an affected tree may cor- 

 rect chlorosis for several years. The tree may be treated through 

 holes, each approximately one-half inch in diameter, bored in 

 the trunk at an oblique angle; the holes should slant downward 



