464 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



the soil becomes contaminated and the 

 trees in their young and tender condition 

 are particularly susceptible to infection 

 through wounds and at the union of stock 

 and scion in root-grafts. 



3. In the orchard the effects of the di- 

 sease are sometimes severe and some- 

 times slight, depending on many condi- 

 tions. Apples do not suffer so much 

 damage as do peaches, berries and other 

 fruits. An attack of crown gall is usually 

 detrimental, often serious, and some- 

 times fatal. A good many affected trees, 

 however, recover or become resistant to 

 the disease. There seems to be little 

 spreading of crown gall in most orchards. 



The Control 



4. In order to keep crown gall under 

 control in the nursery, trees or small 

 fruits should never be grown in land 

 previously infected with the disease. Such 

 plants as become infected should not be 

 allowed to remain in the soil until the 

 galls decay, but should be removed and 

 burned. Neither root nor scion used in 

 root-grafting should come from stock hav- 

 ing galls, or hairy root, and the graft- 

 ing and wrapping should be carefully 

 done. 



5. All nursery stock should be careful- 

 ly inspected and all trees showing evi- 

 dence of crown gall and hairy root or 

 previous cutting-off of galls should be dis- 

 carded. Fruit inspectors should use care 

 in inspecting stock and make sure that 

 every tree condemned is really affected 

 with crown gall or hairy root. All warty 

 appearances are not necessarily crown 

 gall nor are all fibrous roots necessarily 

 hairy roots. A whole shipment should 

 never be condemned because a few trees 

 are infected, since investigation has 

 shown that there is little or no danger 

 of infection spreading from diseased trees 

 to healthy stock in the same shipment. 



6. Growers should never plant a 

 diseased tree. It is better to discard an 

 affected tree than to run the risk that 

 it will never pay interest on the spot of 

 ground it occupies. 



7. Trees which are found affected with 

 crown gall in the orchard should be al- 



lowed to remain if still profitable, but if 

 unprofitable should be removed. Recov- 

 ery sometimes results from the complete 

 removal of galls with sterilization of the 

 wounds. Cutting out is recommended, 

 especially in fire blight districts, since 

 galls afford favorable points for blight in- 

 fection. 



8. On account of the great difference 

 in susceptibility of different varieties, a 

 good opportunity is presented in the di- 

 rection of the selection and breeding of 

 resistant or immune varieties among 

 fruits like the raspberry and grape, and 

 possibly also among some of the tree 

 fruits. 



Biljlioerraphy 



1905. U. S. Department Agriculture, Bu- 

 reau Plant Industry, Bulletin 90, part 



1910. U. S. Department Agriculture, Bu- 

 reau of Plant Industry, Bulletin 183. 



1911. U. S. Department Agriculture, Bu- 

 reau of Plant Industry, Bulletin 213. 



1912. U. S. Department Agriculture, Bu- 

 reau of Plant Industry, Bulletin 255. 



1912. California Experiment Station, Bul- 

 letin 235. 



1913. New Mexico Experiment Station, 

 Bulletin 85. 



Crown Gall and Legume Inocnlation 



The crown gall organism has been 

 found in tumors somewhat resembling 

 the normal nitrogen-fixing nodules upon 

 the roots of alfalfa, crimson clover, and 

 alsike clover. For this reason great care 

 should be taken in using soil or cultures 

 for inoculating legumes in regions which 

 may sometime be used for sugar beets or 

 for orchards. 



It is usually possible to distinguish be- 

 tween the two forms of nodules by their 

 external appearance. The nitrogen-fixing 

 nodules appear to be an outgrowth of the 

 root itself and has no more affect upon 

 the root than any natural outgrowth. The 

 interior of the nodule contains flesh color- 

 ed cells full of bacteria. On the other 

 hand the crown gall tumor causes much 

 distortion of the root, frequently forcing 

 it to branch in many small rootlets which 



