METHOD FOR THE CONTROL OF CROWX GALL 



the question of finding a suitable germicide or fungicide and a 

 suitable dosage which will kill the bacteria and not materially injure 

 the roots of the trees. In this respect the organic-mercury compound, 

 used as a dip in these experiments, represents a distinct improvement 

 over the formaldehyde solution. 



"Well-made grafts properly fitted, especially those which have 

 no overhang at the lower end, were shown by Hedgecock to be less 

 susceptible to crown gall. They have, in fact, less exposed callus. 

 The wrapping, of course, should be thoroughly done, whatever 

 method is selected. Since the material has to be handled so much 

 and since the freshly made grafts will stand thi.s disinfectant, part 

 of the writers' experiments also included dipping'^ the grafts the 

 same day the}^ were made, 

 in order to disinfect and 

 saturate the wrappers with 

 the germicide and to give 

 a second coating to the 

 grafts themselves. 



Since there is still a 

 possibility, after the grafts 

 have been stored and the 

 young tender callus devel- 

 oped, that this may carry 

 incipient infections, and as 

 it is desirable to give an- 

 other dose of the germi- 

 cide just before planting, 

 a third dipping - was tried 

 and found to be noninju- 

 rious to the graft and help- 

 ful in the control. Mellius 

 and Maney* also report 

 the use of Bordeaux mix- 

 ture as a dip for ajDple 

 grafts. 



There is a possibility 

 that the grafting knives or 

 other tools and the benches 

 and taljles may become infected, 

 cases will be eliminated in the 



Fig. 7. — Lot of Ben Davis trees selected as showing 

 some of the best results obtained in controlling 

 crown gall by the use of the organic-mercurj' com- 

 pound. Reading from left to right : Galled trees 

 (none in this case), doubtful (1), clean (99) 



would, of course, escape notice. 



It is not probable that all obscure 

 inspection, and dormant infection 



Furthermore, the knives may cut 

 through bacterial infection beneath the thin outer bark which was 

 not reached by the disinfectant. Although there is no definite proof 

 that stock can be contaminated with crown gall by means of grafting 

 knives, there is proof that the pear-blight organism can be carried 

 on grafting and pruning knives. In view of the fact that it is rather 

 easy occasionally to disinfect the tools and grafting benches, it is 

 thought good practice to utilize this method of control, even though 

 its value is not fully proved. 



' Later experiments in a repetition of these treatments have tended to minimize the 

 importance of the second and third dipping and to increase the importance of the first 

 dipping. 



* Melhus, I. E., and Maney, T. J. A study of the control of cro\\-n-gall on apple grafts 

 in the nursery. Iowa Agr. Exp. Sta. Research Bui. 69, pp. 159-172. 1921. 



