ORNAMENTAL AND SHADE TREES 



231 



The pockets were inhabited by a kind of borer that feeds 

 upon the sap which it gets from the tree by irritating the 

 delicate skin of the callus. The streaks are formed from 

 the surplus sap which, mixed with the excretions of the 

 borers dries on the bark as it runs down the outside of 

 the tree. These borers multiply very rapidly. Their 

 eggs are blown about by the wind in much the same man- 

 ner as fungous spores. Close examination of the bark 

 disclosed numbers of similar dry pockets which harbored 

 all sorts of insect life. Most of the pockets were about 

 four inches long and two inches wide. One caused by a 

 single spur prick was nine inches long and three inches 

 wide. Mealing had been going on four years. The 

 greater part of the damage to come from these wounds 

 had been done or was already brewing. In all proba- 

 bility there were not less than two hundred of these 

 pockets on that hundred foot elm. It would have taken 

 three men at least two days to go over the tree and hunt 

 out and treat all these wounds. This case of spur 

 damage to elm is by no means unique. In one Massa- 

 chusetts town damage of this sort was called to the 

 attention of the tree warden by a telephone lineman. 

 Oak and ash suffer in the same way. 



In the formation of such pockets, the loss of sap- 

 wood and bark impairs the circulation of the tree and 

 reduces its vigor. The loss of sap through the feeding 

 of the grubs is a further drain upon its vitality. The 

 insects, hiding in the pockets where the birds that patrol 

 the crevices of normal bark do not get them, eat the 

 leaves and so reduce the supplies of plant food needed 

 to repair the damage. In this way, even without in- 

 fection, the odds against the life of the tree accumulate 

 from these inconspicuous wounds. 



When the fungi that attack the sapwood. cambium 

 and live bark cooperate with spurs, the damage is 

 quickly, stealthily and thoroughly done. Figure 2 

 shows a sample of the results of spurring followed 

 by sap rot infection. The triangular opening in the 

 bark, to the left of the crack from which the fungus 

 brackets protrude, is a spur mark. 



The upper sides of several limbs of this Norway 

 Maple were spur-marked every few inches for from 

 eight to twelve feet. Almost every spur mark was a 

 center of infection. The entire upper side of each of 

 these limbs was dead when the withering of the leaves 

 and the appearance of the fungus brackets disclosed 

 the injury. The damage to the tree was too widespread 

 to be remedied. 



The fungus which did this damage is a common 

 native species that attacks wounds on many of our 

 broad-leaved and evergreen trees. There are many 

 others with similar habits which mycologists consider 

 more dangerous. 



Maples are relatively thin-barked trees. Infection of 

 thick-barked trees through spur marks would seem less 

 likely. Unfortunately, thick bark is not uniformly thick. 

 The crevices afford better holds for spurs than the ridges 

 do. Even on old thick-barked trees, where the dead bark 

 is tough enough to hold and thick enough at the base 



of the trees to keep spurs from reaching the live tissues, 

 the bark on the upper part of the trunk and upon the 

 branches is relatively thin. 



Chestnut is a fairly thick-barked tree. The one 

 shown in Figures 3 and 4 had been failing noticeably 

 the summer before it was examined. That spring the 

 new leaves on several large branches had dried out 

 when only partially expanded. Those on other branches 

 were dwarfed. The bark over a large part of the trunk, 

 within reach of the ground, sounded hollow. The first 

 patch of it which was removed disclosed the conditions 

 shown in Figure 3. Near the center of the dead area 

 there was a dimple in the wood which corresponded 

 with a spur mark in a crevice of the bark. The spur 

 appeared to have only just pierced the cambium, for the 

 wood was deformed but not splintered. About this 

 dimple was a series of bands of the fungus known as 

 Chestnut Bark Disease. On the other side of the trunk- 

 was another dead patch which came from a spur wound 

 (Figure 4). In this case the spur penetrated the sap- 

 wood and splintered it. The rings of fungus growth 

 show clearly how the disease spread from the jab. In 

 five seasons, unheralded by any outward signs, the fun- 

 gus had grown more than a foot around the trunk and 

 several feet lengthwise. The damage from the other 

 wound was even more extensive. 



The upper sides of the lower limbs of this tree were 

 honey combed with spur marks for a foot or so from 

 the trunk. There was no thick bark there to prevent 

 each jab from puncturing the cambium. One hundred 

 and fifty would be a conservative estimate of the number 

 of spur marks on the tree. The infected branches had, 

 of course, been encircled by the fungus and their sap- 

 wood had dried out. Under the circumstances the only 

 question which could arise as to the fate of the tree was 

 whether it should be removed by inches or all at once. 



From what has preceded, it is evident that when 

 used on living trees spurs can cause heart rot, disfigure 

 their victims superficially, aid the insects and other 

 small animals which attack them, and infect them with 

 sap-rots and bark diseases in so many places at once 

 that treatment is generally futile by the time the damage 

 is doscivered. The carelessly used hatchet or saw can 

 not cause any greater variety of tree troubles, and has 

 the advantage of showing the location of the damage 

 done in time for proper treatment. 



The arborists in charge of valuable collections of 

 trees, belonging to both public and private institutions, 

 have long appreciated the risks run in using spurs and 

 do not permit them to be used upon their trees. Lay 

 owners, who have learned the lesson through the un- 

 timely death of a pet tree, refuse to add to the dangers 

 with which their trees must contend by taking these 

 risks. There are special considerations, such as the 

 economical control of pests upon trees whose replace- 

 ment by other kinds, less attractive to the insects, would 

 be beneficial, which would justify taking the spur risk. 

 Hut, anyone desiring to prolong the life of a tree will 

 keep spurs away from it. 



