THE CANADIAN HORTICULTURIST 



January, 191 1 



Typical blight canker in the bark of a large 

 limb of a Tolman Sweet, which dcTeloped at the 

 base of a watersprout that was inoculated by 

 aphids. Many cankers so caused were on the 

 tree, some of them spreading sufBciently to girdle 

 the limb. 



proboscis into the flower to get the nec- 

 tar, they deposit a few germs in the 

 nectaries, and here the germs develop 

 rapidly, kill the flower, and pass down the 

 bark of the flower stem to the fruit spur, 

 kill it and all the other blossoms on it ; 

 they continue to work their way in the 

 bark, passing on down the twig to the 

 larger branch, and thus we get a typical 

 case of "twig blight." 



When the disease is active in a saupy 

 tree, there is often a gummy exudate from 

 the part affected. This is usually amber- 

 colored and may be seen on the outside 

 of the diseased bark, .sometimes in 

 globules and sometimes slowly streaming 

 down the surface. This gummy mater- 

 ial is teeming with the disease germs and 

 many insects like to feed on it, and in 

 feeding on it they get their feet and mouth 

 parts covered with the germs, and these 

 when they fly away they take along with 

 them. So when they fly from a diseased 

 tree to a healthy one, they are liable to 

 inoculnte the latter with the disease 

 germs fro'" the former. The inoculation 

 is made either through the flower by the 

 honey seekers or else by a puncture of 

 the bark by a bitin? or boring insect, such 

 as a beetle, or bv a sucking insect, such 



as the varioiis^nla^it bugs and aphids. 

 • •• • •• • * • 



We foui\d/Hs the resuW.hf our observa- 

 tions ma^b** in the colle'g^'.prchard and 

 manv oi^l^rds in the Nia^hta, St. Cath- 

 arines aji^ Whitby districtsjvthat fifty per 

 cent, of the total amount •eij; twig blight 

 on an'-ite'-t'tees in igog ^qs due to its 

 spread f rofiii.tf ee; to ^tree n'nd from orchard 

 to orchard bV>'aplTi<^ (Aphis mali and 

 Schizoneura lanigera), and that practical- 

 callv all the twig inoculations that were 

 made after the blossoming season were 

 made by these same orchard pests. 



The aphid's favorite feeding place is 



on the water sprouts, suckers, and 

 young twigs of the tree. It is here they 

 find the tender bark which they can ea.s- 

 ily puncture to obtain the plant juice 

 which is so plentiful there. It is the ten- 

 der, juicy bark that, as we have before 

 mentioned, supplies the ideal conditions 

 for the blight germ to rapidly develop m. 

 An aphid when feeding punctures the 

 bark from which it draws the sap with its 

 sucking tube. Should the twig which it 

 punctures have the blight, the sucking 

 tube which is inserted in the bark will be 

 contaminated with the blight germ, and 

 large numbers of germs will be drawn in- 

 to the body of the insect and will cover its 

 mouth parts, and so, when the aphid 

 moves to another twig, it will carry the 

 germs along with it, and on puncturing 

 the fresh twig will inoculate it with these 

 germs. We found this to be happening 

 in practically all the orchards we visited 

 during June, July, and early August. We 

 found many young trees that had not yet 

 borne a blossom and that were absolutely 

 free from blight before the aphids came 

 in June, to have after this date all their 

 young shoots killed out by the gradual 



Trunk of young pear tree, near the ground, 

 showing a rapidly spreading canker, which de- 

 veloped as tha result of the tree being inoculated 

 with the germs of the shot-hole bark-boring 

 beetle, Scolytus rugilosus. The minute borings 

 of the beetle may be seen close to the arrow 

 points. Notice that the borings are usually 

 within a bud scar. 



spread of the di.sease from the tops down- 

 ward after they had been inoculated by 

 aphids. We also found large numbers of 

 suckers and water sprouts on the older 

 trees develop the disease after the aphids 

 visited them and rapidly die. 



In many cases, when the disease reach- 

 ed the base of the water sprout or sucker 

 it entered the limb or trunk on which the 

 shoot grew and there formed a canker, 

 sometimes large and spreading, if the 

 bark was juicy, and sometimes small. 

 The bark immediately surrounding such 

 cankers is liable to harbor the disease 

 germs through the winter, then in the 

 spring, when the sap begins to run once 

 more, the germs rapidly develop, spread 



Shot-hole borings in a healthy branch from a 

 young pear tree. In every case they are at the 

 base of a fruit spur or small branch. Around 

 three out of five of the punctures the blight was 

 spreading as a canker. 



further through the bark, thus enlarging 

 the canker, and often girdling the limb, 

 which results in its death. 



THE DISEASE IN NUE8EEIE8 



We found aphids to be the principal 

 means of spreading the blight in apple 

 tree nurseries. Wherever in nurseries 

 the aphids were kept in check there was 

 practically no blight. While in the nur- 

 series in which the aphid was allowed to 

 have its way, there the blight flourished 

 in all directions. 



While aphids and "twig blight" are 

 both common on the apple, neither are 

 very prevalent on the pear. Blight, how- 

 ever, kills off many more pear trees than 

 apple trees. How, then, is the blight 

 carried to the pear trees? It is some- 

 times carried to the blossoms by bees and 

 wasps, and it is such inoculations that 

 are responsible for most cases of "twig 

 blight" in the pear. "Body blight," how- 

 ever, is more common than "twig 

 blight" in the pear. This is the same dis- 

 ease working in the bark of the trunk and 

 larger limbs. The germs sometimes en- 

 ter it at the base of the twigs which have 

 been inoculated at the blossoms. We 

 found, however, during the last two sea- 

 sons cases of direct inoculation into the 

 bark of healthy trees made by the fruit- 

 bark-boring beetle (Scolytus rugulosus). 



This is the same beetle that works in 

 the bark of the peach and cherry, caus- 

 ing them to exude large quantities of 

 gum-like material. The pear tree does 

 not exude this gummy material, and as 

 the hole made by the beetle is very small 

 and is usually underneath a bud or spur, 

 it is not readily seen. This beetle bores 

 in the bark and is more common on weak 

 or diseased trees than on healthy ones. 

 We found the beetles in the bark of 

 blighted trees to be literally covered with 

 blight germs, and we found the disease 

 to be developing around the fresh punc- 

 tures made bv these beetles in the bark of 

 healthy trees. The fruit-bark-boring 

 beetle is one means of spreading the 

 blight among pear trees. 



The pruning-knife, saw, chisel, shears, 



