APPLE DISEASES 



463 



are known to occur among stone fruits as 

 well as among apples. 



Small Fruits 



Raspberries, blackberries, loganberries 

 (Figs. lCand3) are often affected with 

 crown gall and probably other small fruits 

 are also attacked. The disease not only 

 causes galls on the roots, but on the 

 blackberry, at least tumors often break 

 forth in long lines from the interior of 

 the canes. A case of what appeared to 

 be hairy root on blackberry was sent to 

 the Department of Plant Pathology dur- 

 ing the summer of 1912. Considerable 

 damage seems to result from the effects 

 of the disease on these fruits and it 

 is probable that soil infection and the 

 spreading of the bacteria through the 

 ground to healthy plants is much more 

 serious than among orchard trees. Fruit 

 trees should never be set immediately 

 upon ground from which galled berry 

 bushes have been grubbed out. 



Grapes 



Most of the European varieties of 

 grapes are quite susceptible to crown gall, 

 while only a few of the American varieties 

 are considered susceptible. On the grape 

 the disease is found in two forms, as a 

 root gall and as a cane gall. On cuttings 

 and young plants the root form is most 

 commonly found. These root galls are 

 usually formed at a wound and conse- 

 quently occur frequently at the graft 

 union on grafted vines. On older plants 

 the disease usually also attacks the stem 

 extending from the crown upwards. On 

 the canes the galls are usually confluent 

 and occur in lines running lengthwise of 

 the stem. The effect of the galls is to 

 stunt the vines. The leaves are frequent- 

 ly smaller and show poor color. The un- 

 derground galls decay each year and 

 other rot-producing organisms may gain 

 entrance and aid in finally bringing about 

 the death of the vine. The cane galls 

 are reported commonly to start from in- 

 fection in frost cracks. They may also 

 start in wounds made by pruning or in 

 any other way. The disease is spread in 

 the vineyard in various ways, such as by 



the water of irrigation, use of diseased 

 cuttings and by insects. 



No cure is known for plants that are 

 already diseased and no definite recom- 

 mendations can be made for the grower 

 of European grapes. It is suggested, how- 

 ever, that where the disease is preva- 

 lent, it would be worth while to try out 

 experimentally some of the stocks recom- 

 mended as resistant under more southern 

 conditions in the United States with a 

 view to using such as may prove hardy. 

 In New Mexico, where crown gall has 

 been very serious, the Rupestris St. 

 George, Sweetwater, Seedless Sultana, 

 Matosa and some others are found re- 

 sistant and succeed on their own roots. 

 Benefit has also resulted in the south 

 from grafting the susceptible varieties 

 on such resistant stock as the Rupestris 

 St. George and Lenoir. Among the most 

 susceptible varieties are the Mission, 

 Muscat of Alexandria, Flame Tokay, Mal- 

 aga and Rose of Peru. 



The following precautions should be 

 taken whenever susceptible grapes are 

 grown: Secure cuttings where possible 

 from vineyards free from disease. Where 

 frost is troublesome and infection occurs 

 in the resulting frost cracks, plant deep or 

 protect with some covering. It is best 

 for the grower by propagating his own 

 stock to avoid the possibilit.v of introduc- 

 ing crown gall through grafts or cuttings 

 from infected districts. 



Hops 



Crown gall is reported as serious on the 

 hop in some sections. Affected plants 

 should be removed and burned. 



SUMMARY 

 The Disease 



1. Crown gall in its various forms, 

 which occur on a great variety of plants 

 in many parts of the world, is caused by 

 parasitic bacteria which enter the living 

 cells of the host and stimulate them in 

 some way to multiply excessively, thus 

 producing tumors, the presence of which 

 is usually detrimental to the welfare of 

 the plant. 



2. The greatest losses resulting from 

 crown gall occur in the nurseries where 



