CARTER: ILLINOIS TREES: THEIR DISEASES 13 



and penetrate the sapwood to a depth of only 1 or 2 inches. The 

 iron, in the form of iron citrate, may be placed in the holes as 

 a dry powder in large gelatin capsules or forced into the trunk 

 in water solution by use of special equipment. The usual dosage 

 is 5 grams of iron citrate per inch of trunk diameter. Best re- 

 sults from this method of treating are obtained when the iron 

 citrate is applied before leaves appear in the spring. 



More lasting results are obtained through soil treatment 

 than through either of the treatments described above. Equal 

 parts by weight of iron sulfate and sulfur are added to the soil. 

 The sulfur is added to acidify the soil. Iron is changed to soluble 

 forms in acid soil. To stimulate growth of chlorotic trees, the iron 

 sulfate and sulfur should be supplemented with tree food, as 

 described in the section "Feeding." The iron sulfate and sulfur 

 mixture is supplied at the rate of 1 to 3 pounds per inch of trunk 

 diameter at breast height. The heavier rate of application men- 

 tioned is for trees over 6 inches in diameter. Trees that do not 

 respond to a single treatment should be retreated in succeeding 

 years. 



Chelated iron and other specially prepared iron compounds 

 have been recommended as being more effective than iron sulfate 

 for correcting chlorosis, especially in alkaline soils. These types 

 of materials are sold under various trade names and should be 

 used as recommended by the manufacturers. 



Chemical Injury. — In recent years chemical injury to trees 

 has become frequent, largely because of the common and wide- 

 spread use of herbicides such as 2,4-D, and 2,4,5-T. Injury caused 

 by spray drift or vapors of 2,4-D and 2,4,5-T appears as de- 

 formed growth or dying of trees. In mild cases of injury the 

 leaves of some trees, such as elm, hackberry, hickory, honey 

 locust, and oak, may become thickened and leathery; the tips 

 and margins of the leaves may be cupped downward or the leaves 

 may be rolled. More severe injury may cause leaves to grow long 

 and narrow and the veins to appear unusually prominent. Se- 

 verely injured leaves of cherry, birch, black locust, elm (Fig. 

 15), ha\\i;horn, honey locust, Russian olive, sycamore, and walnut 

 may become twisted or rolled and appear boat shaped or curled 

 into ram's-horns. In time the leaves die. Many trees recover in 

 succeeding years from mild injury caused by 2,4-D and 2,4,5-T. 

 Feeding to stimulate growth may aid in their recovery. Severely 

 injured trees may have many branches killed, or the trees them- 

 selves may die. 



