102 



Crown-Gall. 



Crown-gall is of importance chiefly in the nursery. It is 

 not unusual to find whole blocks of nursery trees affected by 

 this disease. Affected trees, when set in the orchard, some- 

 times grow out of the disease, but they are more likely to 

 show retardation in growth and stunted development. Crown- 

 gall is not confined to the apple but attacks many kinds of 

 plants and trees. The disease also is known as crown-knot, 

 root-gall and, in one form, as hairy-root. 



The causal organism of crown-gall is Bacterium tumefaciens. 

 It infests cultivated soils and lives in old galls of a great 

 variety of plants. It is doubtless true that some soils become 

 more badly contaminated with the organism than others. 



The most familiar and common form of the disease occiu's 

 as galls at the base of the trunk or on the branches. In the 

 nursery, a large proportion of these galls form just above the 

 union of scion and stock. They are usually an inch or two 

 in diameter, but may be larger, and, when developed, hard 

 and rough. (Fig. 18.) A second form of the disease, less 

 common than the galls, takes the form of an excessive devel- 

 opment of fibrous roots, which grow in dense clusters, sug- 

 gesting the name, hairy-root. (Fig. 19.) 



Control of crown-gall is largely a matter of sanitation and 

 avoidance. The nurseryman should use the utmost care in 

 preparing his stock. Grafting instruments should be fre- 

 quently disinfected in a 1-1,000 solution of corrosive subli- 

 mate; the graft union should be carefully made and wrapped. 

 Where the disease is discovered in the nursery, affected trees 

 should be promptly removed and burned. If a large number 

 of nursery trees are diseased, they should be cleaned out and 

 the land planted to other crops for several years. No method 

 of disinfecting the soil for this trouble is known. 



Orchardists should insist on clean nursery stock when se- 

 lecting trees for new orchards, and every tree should be care- 

 fully inspected before setting. All that show any evidence of 

 crown-gall or hairy-root should be rejected. 



