Page Eight 



BETTER FRUIT 



April, 1922 



Crown Gall, Its Causes and Cure 



ROOT knot, crown gall, or black 

 knot that affect all stone fruits and 

 nuts and even apples and pears, 

 seem to be native to many of our soils. 

 There are numerous instances of crown gall 

 in nurseries on land where tree have never 

 been grown before. No nursery on the 

 coast can boast of having never had a 

 knotted tree, though no affected tree is 

 knowingly permitted to go out for planting. 

 The black knot on the vine is said to be 

 the work of the same species of bacterium 

 that produces tumors on peaches, almonds, 

 etc., and is found all over the world, on 

 many kinds of trees, bushes, vines and 

 plants. In vineyards the aerial form is not 

 infrequently found growing on one-year 

 wood, and this is attributed to injury from 

 early frosts and the. infection entering the 

 cracked bark. On trees, as every one knows, 

 the galls that we have learned to dread are 

 those that occur near the surface of the 

 ground, or on the main roots near the 

 surface. 



In an excellent discussion of the disease 

 in the Sunszveet Standard, M. A. Benjamin 

 tells how to go about curing it. The grower 

 should dig down around his trees where 

 conditions of growth indicate trouble, look- 

 ing for root-knot just in the same way as 

 he does for borers. It is only on the 

 crown or the main roots that work is applied 

 — don't bother about any knots that may be 

 on roots aw.iy from, the tree. When gall or 

 root-knot is found, cut it out with a chisel 

 or gouge, cutting down in the center till 

 a concave is formed, because it seems to go 

 down to a core like a corn. 



After having been thoroughy cut out 

 clean and the chips cleared away, the wound 

 is disinfected with a strong creosote and 

 then painted with a good stiff roofing 

 paint. The aerial form, that is galls ap- 

 pearing on the trunk or on the branches 

 above the ground — are always easily des- 

 troyed, but the others need more attention 

 later in case of reinfection. 



Those trees whose habit it is to be 

 shallow-rooted have shown themselves to be 

 more susceptible to root-knot. This may be 

 because the roots are more easily subject 

 to injury from plow or cultivator than those 

 rooting deeper. It is suggested that a good 

 many galls appearing just below the surface 

 are the result of injury by gophers, the gall 

 bacteria entering through the wounds so 

 made. 



While infection undoubtedly takes place 

 during the dormant season, it remains latent 

 till growth starts in the spring and the galls 

 form during the actual growing season. 

 The rate of the growth of galls as well as 

 the appearance of new galls is proportionate 

 to the growth the trees make. 



There seems to be a steady rise in the 

 rate of appearance of new galls from the 

 first to about the sixth year; a slackening of 

 the pace for a couple of years following, 



with a possib.e decline in later years, when 

 the rate of growth is decreased or it comes 

 to a standstill. It should therefore be pos- 

 sible, by removing the galls from the trees, 

 during the first eight years or so, during 

 which nearly all their growth is made, to 

 ultimately reach a condition when there 

 would be so few new galls coming as to be 

 every year for good results. 



As for reinfections, while these do occur, 

 the low rate of their appearance, something 

 like ten per cent, is not such as to warrant 

 great concern. 



A lower rate of reinfection might be 

 obtained by using some soil stimulant con- 

 taining copper sulfate, which has been 

 successfully used by the writer. This will 

 have to be used with caution. 



Tree from which crown gall has been thoroughly 



chiseled out. 



{^Courtesy Sunsweet Siandard) 



CROWN gall bacteria cannot enter into 

 perfectly sound tissue and infect it. 

 There must be a wound or abrasion — no 

 matter how small. It is hard to account 

 for some galls on the basis of mechanical 

 injury. Most of those one finds are ap- 

 parently traced to bruises caused by over- 

 lapping roots galling one another so as to 

 expose interior bark. Judicious pruning of 

 the roots at planting time will help reduce 

 this risk. 



The practice of leading water to the base 

 of trees with a shovel is to be deprecated. 

 There are no feeding roots there to render 

 it necessary and there is danger of injury 

 to the tender bark of the roots through 

 which infection may enter, the moisture 

 aids in the production of fungus and 

 bacteria. 



In treating some trees for crown gall, it 

 is necessary, in cutting it out, almost to 



girdle the tree and when this is done it is 

 best to bridge graft. When doing this you 

 are supplying the upper part of the trees 

 with nourishment. 



The important step in bridge grafting is 

 preparing the wound to receive the grafts. 

 The injured parts should be thoroughly 

 cleansed, all dead tissues cut away and the 

 cleansed surface should be treated with 

 creosote and then painted. The irregular 

 edges of the bark should be cut back evenly. 



The scions which form the bridge should 

 be selected from wood of the previous sea- 

 son's growth. Either branches which grew 

 the preceeding season or water sprouts that 

 are only one year old may be used. 



It is important that the scions should be a 

 little longer than the space to be bridged. 

 This is in order that the middle portion of 

 the scion, when put in position, shall arch 

 slightly over the central part of the wound 



Before being placed in position, the 

 scions are beveled at each end, both surfaces 

 being on the same side of the scion. This 

 beveling should be done with a long, slop- 

 ing cut, so that the wedge-shaped ends thus 

 formed will be relatively thin, to permit 

 their being thrust well under the bark with- 

 out danger of separating it unduly from the 

 cambium at the points of insertion. The 

 placing of the scions in position is facili- 

 tated if the bark at the margins of the 

 wound is slit for a short distance at the 

 points where the ends are to be inserted. 



The number of scions required for a 

 bridge will depend largely upon the size 

 of the trunk. No fixed rule can be given. 

 The larger the number the more complete 

 will be the restoration of the connection 

 between the parts above and below the 

 wound, but if placed too close together the 

 bark at the margins of the wound between 

 the scions will be raised. The starting of 

 the bark except at the immediate points of 

 insertion of the scions must be avoided. 



In placing the scions it is of the greatest 

 importance that the cambium of the scions 

 which are exposed in the sloping cuts at 

 the ends be brought into intimate contact 

 with the cambium that lies under the bark 

 at the margins of the wounded area. 



THE union of scion and tree can occur 

 where the cambium layers of the two 

 come together. The scions may be secured 

 in their proper position, if need be, by 

 driving a very small nail through each end 

 into the trunk. This vvill aid in drawing 

 the cambium of scion and trunk closely 

 together. The operation is completed by 

 thoroughly covering the area occupied by 

 the ends of the scions and the margins of 

 the wound with grafting wax, strips of 

 waxed cloth, or by some other means that 

 will adequately prevent these parts from 

 drying out. 



If the wound is mostly below the surface 



(Continued on page 27) 



