Keeping Shade Trees Healthy 



filled-in soil and the complete decom- 

 position of the organic material slowly 

 reduces permeability of the soil to air 

 and the roots die slowly from suffoca- 

 tion. Eventually the tops of trees with 

 damaging earth fills over their roots 

 begin to die back. Often they blow 

 over in storms the stubs might have 

 rotted below the soil line and for some 

 distance above it; oxygen starvation of 

 the roots combined with wood decay 

 has finally killed the tree. 



How can one tell whether an earth 

 fill has been made over the root area 

 of a tree? Normally the base of a tree 

 at the ground line and just above it is 

 greater in diameter than the main 

 trunk a few feet above the ground. A 

 buttress or flaring of the trunk just 

 above the ground line indicates that 

 it has grown normally at that soil level. 

 However, if the trunk enters the 

 ground without expanding, flaring, or 

 buttressing, one should be suspicious 

 that an earth fill has been placed over 

 the roots. The soil around the base of 

 the trunk should then be removed to 

 determine if a fill has been made. 



The bad effects of a fill can often 

 be prevented or overcome by installing 

 drain tiles in the soil. The tiles should 

 be placed at the old soil level. They 

 should open into a well built around 

 the base of the tree. This well can 

 either be left open or can be filled with 

 coarse stones. The tiles may be installed 

 either in a radiating pattern or be laid 

 in parallel lines. In either case they will 

 provide both aeration and a place to 

 introduce water during drought. 



MANY DISEASES of shade trees are 

 caused by parasitic fungi and bacteria. 

 Some virulent parasites will attack and 

 disfigure or kill trees even though they 

 are growing under the best possible 

 conditions. Many weak parasitic or- 

 ganisms, however, that do practically 

 no damage when trees are growing 

 well can destroy trees that grow under 

 poor conditions. 



To avoid the attacks of many kinds 

 of twig blights and trunk and branch 

 cankers caused by weakly parasitic or- 



93 



ganisms, give your trees the best pos- 

 sible growing conditions keep them 

 well fertilized, provide organic mate- 

 rial in the soil, make certain that the 

 soil is permeable to air, and water ade- 

 quately during droughts. 



Many of the virulent fungus para- 

 sites can be controlled by the applica- 

 tion of fungicides, but for others no 

 means of control are yet available. 

 Some diseases can be prevented by con- 

 trolling the insects that spread them. 



Most leaf diseases (which do their 

 damage by reducing the ability of the 

 leaves to make sugars and other foods 

 needed for growth and other normal 

 functions) can be controlled by spray- 

 ing with fungicides. Sycamore an- 

 thracnose, a destructive fungus disease, 

 will respond to pruning of the cankered 

 branches and spraying with a fungi- 

 cide two or three times in summer. 



Bordeaux mixture is the commonly 

 recommended fungicide. For this work 

 power sprayers are usually necessary. 



Leaf spots of elm, maple, horsechest- 

 nut, ash, and many other kinds of 

 trees can be controlled by spraying. 



Many leaf diseases are not suffi- 

 ciently serious to warrant spraying for 

 them. They ordinarily will not kill a 

 tree in one season, but if the attack is 

 serious year after year, great damage 

 may result. 



The fungi that cause cankers of the 

 limbs and branches can often be con- 

 trolled by removing the diseased 

 branches or by cutting out the cank- 

 ered tissues. When cankers are excised, 

 the wounds should be painted with an 



Illustrated on the next two pages are the 

 form and comparative size of commonly 

 planted shade trees. They are drawn to 

 scale; the distance between the horizontal 

 lines is 1 feet. Another point brought out 

 is one that home owners often overlook a 

 young tree, 2 or 3 feet high when it is 

 planted, may in time grow into a giant, and 

 therefore should not be planted too close 

 to a house. The drawings were made by 

 Rudolph A. Wendelin; the original silhou- 

 ettes were prepared by Marguerite M. Mc- 

 Cormick, under the direction of Curtis 

 May, of the Bureau of Plant Industry, Soils, 

 and Agricultural Engineering. 



