Page T-ceJvr 



BETTER FRUIT 



June, 1922 



Pear and Apple Blight in Montana 



Botanist and Bt 



BACTERIAL blight of apples and 

 pears was first seen in New York 

 State about 1792 and since that time 

 has spread over the entire United States, 

 doing untold damage to pomaceous fruits. 

 While the greatest destruction has been in 

 the pear-growing valleys of California, the 

 losses in apple orchards also have been very 

 heavy. Certain parts of the Rockv Moun- 

 tain region were the last to be invaded by 

 this disease. It did not reach Montana 

 until about 1905, when it made its appear- 

 ance near Hamilton. The writer made 

 strenuous efforts to get the disease stamped 

 out, but received the support of only a few 

 of the fruit growers, the others being un- 

 able to realize the seriousness of the situa- 

 tion. The State Board of Horticulture 

 was not at that time organized to a point 

 where it could handle the situation. 



Apparently separate introductions of the 

 disease were made, probably with nursery 

 stock, into other parts of the state. At 

 Miles City and at Laurel the blight had 

 made such great headway before being 

 reported that its eradication would have 

 required much labor and expense, but at 

 most other points it could have been eradi- 

 cated at relatively small cost had the recom- 

 mendations of the Experiment Station been 

 carried out. In three instance the disease 

 was so quickly brought under control that 

 very little damage was done. 



The spread of the blight through the 

 apple orchards has been rapid, and thou- 

 sands of fine, thrifty trees have been 

 destroyed entirely. At the present time it 

 may be found in every part of the state. 

 This is, however, but a repetition of the 

 experience of most other states throughout 

 the country. 



For a period of several years the State 

 Board of Horticulture made a most deter- 

 mined fight against apple blight and suc- 

 ceeded in bringing it under partial control, 

 largely by the wholesale elimination of 

 very susceptible varieties such as the Trans- 

 cendent crab. The disease now appears 

 some years as an extensive twig blight, kill- 

 ing a few large limbs and trees, and some 

 years as a very light and scattered infection, 

 doing but little damage. 



Cause and Symptoms of Blight — • 

 This blight is caused by a bacterial organ- 

 ism, a parasite quite unlike insects and 

 fungi. It attacks principally the apple, 

 pear, and quince. A very light infection 

 that soon dies out may occasionally be 

 found on stone fruits, and on service berry, 

 hawthorn, and some other pomaceous shrubs. 

 It never attacks willows, poplars, and other 

 wild plants that are not related to the 

 apple. 



The blight germs gain entrance to the 

 trees in several ways: (1) Through wounds 



Bij Deane B. Swingle, 



i-tenolos,isl, Montjua Agruultural Experiment SlJlion, Bo~eman 



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I Bacterial blight in fear and apple | 



I trees, a disease difficult to control in | 



I the better organized fruit districts, \ 



I has been even more troublesome in \ 



I sections where orchardists are neg- \ 



I lectful of approved practices. The \ 



I article that follows carefully presents % 



I both the causes and the remedies. % 



I It should provide the incentive | 



I necessary to stir the owner of every | 



I orchard where blight makes it ap- | 



I pearance to adopt the drastic Tnea- \ 



I sures by which it may be eradicated . \ 



I Those contemplating new plantings | 



I will find here a helpful guide in the | 



I matter of susceptibility of varieties I 



I to the blight. | 



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made by pruning tools, cultivators, etc.; 

 (2) through bites of insects, particularly 

 the green aphis; (3) through the open 

 flower, to which it is carried by bees, ants, 

 and other insects, and, as has recently been 

 shown, by the wind. When once the germ 

 gains entrance it multiplies rapidly and 

 works downward through the bark, but may 

 not cause any visible effect until weeks 

 after the infection has taken place, so that 

 the grower is badly deceived as to just 

 when the disease was acquired. 



The following symptoms are very char- 

 acteristic: If the infection begins in a 

 flower cluster or in the end of a shoot, as 

 it usually does, the leaves first wilt and 

 droop, then turn brown in the apple and 

 nearly black in the pear. Soon they become 

 dry, hard, and brittle. The bark of the 

 affected twig likewise becomes slightly 

 darkened in the apple and nearly black in 

 the pear. The line between the diseased 

 and the healthy bark is not sharp and dis- 

 tinct during the growing season, so that it 

 is often difficult to determine just how far 

 the disease has progressed; and it is usually 

 farther than an inexperienced person would 

 suppose. On cutting into the diseased bark 

 one finds the inside at first pinkish in 

 color instead of a healthy green, but when 

 it has been diseased for a few weeks it 

 becomes darkened through to the wood, 

 which remains nearly white and normal. 

 This is essentially a bark disease and will 

 continue, in susceptible varieties, to run 

 down the limbs and trunk into the roots, 

 sometimes killing the tree outright in a 

 single season. It practically ceases to spread 

 downward at the end of the growing sea- 

 son and becomes dormant during the 

 winter, but with the opening of spring 

 activity is renewed and another stretch of 

 b.uk is killed. This continues until the 

 tree is completely overcome. Sometimes 

 the attack begins in the water-sprouts at 



the base of the tree. Under these circum- 

 stances it reaches the roots in a few weeks, 

 where it can not well be treated, and the 

 case becomes practically hopeless. 



There is a general impression that plants 

 or animals that are very vigorous resist 

 disease better than those that are generally 

 unhealthy and stunted. This certainly is 

 not the case with apple and pear blight. 

 In slow-growing trees the disease makes but 

 moderate progress downward through the 

 bark and generally dies out without reach- 

 ing the larger limbs, while in very rapidly 

 growing, vigorous trees it progresses rapidly, 

 sometimes running through the bark from 

 the tips to the roots in a single season. 



/^FTEN there may be seen on the 

 ^—'blighted leaves and branches, and espe- 

 cially on the blighted fruits, a yellow exud- 

 ate in tiny droplets, or even in larger 

 quantities running down the tree. This 

 contains enormous numbers of the germs of 

 the disease and is freely visited and eaten 

 by ants, wasps, bees and probably other 

 insects, that carry it to other trees, espe- 

 cially to the flowers, where a fresh attack 

 begins. A single bee may thus infect 

 several hundred flowers during the season, 

 and a swarm of bees could infect many 

 thousands. This accounts in most cases for 

 the very extensive and sudden attacks that 

 many orchards have suffered. 



When the healthy leaves have fallen in 

 the autumn, those on the diseased twigs 

 and branches still cling to the tree, where 

 they are very conspicuous. At this time 

 also the diseased bark has turned quite dark, 

 especially in the pear, and the line between 

 it and the healthy bark is more sharp and 

 distinct than during the summer season. 

 Here, in the deeper layers of the bark, in 

 the line between the diseased and the 

 sound tissues, the bacteria that cause the 

 blight live over winter. On the assumption 

 that they do not live over in the ground or 

 anywhere else excepting the region just 

 indicated, the following treatment is ad- 

 vocated by the United States Department 

 of Agriculture and by many of the experi- 

 ment stations, and is extensively practiced 

 by orchardists with some measure of success. 



Treatment ok the Blight — In a 



single sentence we can say that the only 

 known method of curing a blighted tree is 

 to cut out and burn all affected parts. 

 This seems simple enough, but there are 

 important details that determine between 

 success and failure. As a matter of fact, 

 very few inexperienced men are successful, 

 largely because they will not pay close 

 enough attention to these important details. 

 The following rules should therefore be 

 thoroughly mastered and rigorously fol- 

 lowed: 



