﻿14 BULLETIN 24, IT. «. DEPARTMENT OP AGRICULTURE. 



As with all species, the demand of cottonwood upon light varies 

 with the amount of moisture in the soil, and occasionally trees sur- 

 vive under shade, provided moisture* conditions are exceptionally 

 favorable. 



SUSCEPTIBILITY TO INJURY. 



Cottonwood is fairly windfirm, but in exposed situations it is 

 likely to suffer from breakage on account of the brittleness of its 

 branches. Windfall is common only on rather wet, poorly drained 

 sites, where the roots He near the surface. In well-drained soils cot- 

 tonwood sends a rather stocky taproot, well reenforced with spread- 

 ing laterals, down to a depth of 4 to 6 feet. 



Damage from fungi is not serious in the Mississippi River Valley. 

 On unfavorable sites, however, especially in plantations outside its 

 natural habitat, injuries from this source are often more or less pro- 

 nounced. Of the several diseases, the most common and injurious is 

 the " rust," caused by a fungus (Uredo melampson medusre Thiim.), 

 which is said materially to check the growth of the tree. This and 

 many other leaf fungi are likely to do considerable injury to young 

 trees in the nursery. In such instances it is advisable to burn the 

 diseased leaves at the end of the growing season. Spraying with 

 Bordeaux mixture is often effective. 



Of the fungi attacking the wood of cottonwood, Forties applanatus 

 (Pers.) Gill * (Elvingia megaloma (Lev.) Murrill),is one of the most 

 noticeable, but seldom gains entrance to perfectly sound trees. It 

 attacks both heartwood and sapwood, causing a white rot that weakens 

 and sometimes kills the tree. Wounded and fire-scarred trees are 

 most liable to such injury. Other fungi attack the twigs and 

 branches of cottonwood. These include species of Cytospora and 

 Nectria, which cause dead spots or cankers in the bark, resulting in 

 the death of branches beyond the point affected. Very little is 

 known of some of these fungi, but as a rule they seldom do serious 

 damage in cottonwood stands, and expensive measures for combat- 

 ing them are rarely justified. The ordinary procedure in case of 

 widespread fungous attacks is to cut out all diseased trees and burn 

 or remove them. 



The cottonwood in the southern United States is subject to damage 

 by the mistletoe, Phoradendron flavescens (Pursh.) Nutt. 2 Injuries 



1 Ileald. F. D. A disease of cottonwood due to Elvingia megaloma, Nebr. Agr. Expt. 

 Sta. Rept., vol. 19, pp. 92-100, 1906. 



2 Bray, W. L. The mistletoe pest in the Southwest. Bureau of Plant Industry Bul- 

 letin 166, February, 1910. 



