The Apple Leaf Blister Mite 



THE apple leaf blister mite is an old 

 enemy under a new guise. It has been 

 known for many years in Ontario 

 as a pest of the pear, but it is only 

 within the last few years that its injuries 

 to the leaves of apples in Ontario have 

 been observed and have become worthy 

 of serious attention. In Europe, how- 

 ever, this pest has for a long time been 

 observed on apple leaves. 



The leaf blister-mite is not a true in- 

 sect ; it belongs to the group called 

 Acarina, and is known to science as 

 Eriophyes pyri. It is a very minute crea- 

 ture about 1-125 inch in length, hardly 

 visible to the naked eye. It has four legs 

 and a worm-like body divided into a 

 large number of rings by fine lines, and 

 provided with a few pairs of stiff hairs. 

 For the main facts regarding its habits, 

 I am indebted ot Professor Parrott of the 

 New York Agricultural Experiment Sta- 

 tion, Geneva, N. Y., who has made a 

 special study of this mite and many oth- 

 ers of the same group ; and who has very 

 kindly given me the latest information 

 he has obtained in his investigations of 

 a different subject. 



LIFE HISTORY 



The leaf blister-mites feed by sucking 

 the juices of the buds and leaves. They 

 pass the winter under the scales of the 

 buds, frequently in colonies. In spring, 

 as the young leaves unfold the mites 

 move out upon them, and soon burrow 

 through the skin of the underside, and 

 feed upon the juices of the soft tissues 

 within. Through the irritation produced 

 by these operations galls or blisters are 

 formed. Within these galls eggs are de- 

 posited which hatch in a few days, and 

 the young mites feed on the juices of the 

 leaf. When mature they pass out of the 

 leaves through openings made on the 

 wider surface and betake themselves to 

 other leaves to repeat the same process. 

 Throughout the growing season the pro- 

 duction of mites continues, and not until 

 October do they desert the leaves for the 

 buds, where they hibernate. 



NATURE OF INJURY TO LEAVES 



As already stated, the main injuries 

 are those done to the leaves, but the fruit- 

 stems and fruit are often injured. The 

 galls on pear leaves are at first greenish, 

 then reddish, afterwards bright red, and 

 (inally, with the death of the affected tis- 

 sues, brown or black, often most conspic- 

 uous on the sides of the midrib. When 

 the mites are very numerous the injuries 

 produce defoliation of the trees. 



The color of the galls on apple leaves 



•Since this paper was prepared and read at the 

 last convention of the Ontario Fruit Growers' 

 Association, the bulletin referred to in the con- 

 cluding paragraph has been published. Extracts 

 from it may be found on page 62 of this issue. 



Prof. W. Lochhead, Macdonald College 



is much less striking than that on pear 

 leaves. The galls are usually more abun- 

 ant on the margins of the leaves and are 

 at first greenish, soon becoming brown- 

 ish, and only occasionally red. The co- 

 alescence or merging together of several 

 of the galls produce irregular shaped 

 dead areas, which often rupture at the 

 margin. Parrott says: "About July ist 

 the most striking effects of the mites 

 upon the leaves appear, especially if there 

 is much yellowing of the foliage, as fre- 

 quently occurs. Upon the upper sur- 

 faces of such leaves the mite-infested 

 spots are of a light brown or of a dark 

 green color, and are uniformly brown 

 beneath. These spots are t+iickly massed, 

 forming a dark broad band of irregular 

 width along each side of the leaf, which 

 contrasts conspicuously with the inter- 

 vening light yellow area about the main 

 rib. To one standing on the ground 

 and viewing the leaves from beneath, 

 this striping of the leaves is very sug- 

 gestive of variegated foliage of certain 

 ornamental plants." 



REMEDIES 



Cultural methods are of little value in 

 dealing with this pest. Careful pruning 

 will, of course, rerrfove large numbers of 

 the mites, but it will not exterminate 

 them. I believe Professor Gillette, then 

 of Michigan, first suggested in 1886 the 

 use of strong soap suds, kerosene emul- 

 sion during the dormant season as a 

 means of control on pears. In 1890 Pro- 

 fessors Comstock and Slingerland of Cor- 

 nell University, published (Bulletin No. 

 23, C. U. Agr. Exp. Sta.) the results of 

 some experiments with kerosene emul- 

 sion in the control of the blister mite on 

 pears. In 1893 Professor Slingerland 

 published (Bulletin No. 61, C. U. Agr. 

 Exp. Sta.) the results of successful ex- 

 periments using kerosene emulsion. He 

 said: "Our experiments strongly indicate 

 that the pear leaf blister can be nearly 

 exterminated in a badly infested orchard 

 by a single thorough spraying of the 

 trees in winter with kerosene emulsion 

 diluted with from five to seven parts of 

 water. ' ' 



All these experiments had to do with 

 the leaf blister-mite on pears. In the at- 

 tempt to deal with the same pest on ap- 

 ple trees, however, it was found a more 

 difficult task. The Geneva station has 

 made many experiments. In Bulletin 

 283, published December, 1906, the fol- 

 lowing recommendations are (given, 

 bassd on spraying operations carried on 

 for two years : 



(a) Whale oil soap solution not effec- 

 tive. 



(b) Miscible oil (one part to twenty of 

 water) effective. 



(c) Kerosene emulsion (one part to 



eight of water) effective. Two sprayings 

 are better than one, but if only one is 

 practicable, make the application in early 

 fall as soon as possible after the leaves 

 have fallen. 



(d) Kerosene pure, effective, but fruit 

 crop lost. 



Since the publication of Bulletin No. 

 283 the experiments have been continued, 

 and new ones added ; and, as a result of 

 two more years' work. Professor Par- 

 rott informs me in a letter dated October 

 22nd, 1908, that in a bulletin soon to be 

 published, he will recommend strongly 

 the lime-sulphur wash applied in the dor- 

 mant season just before the buds burst. 



A Lesson in Grafting 



The accompanying illustration of a 

 Pewaukee apple tree grafted on crab 

 stock, teaches a lesson. It shows that 

 vigorous growing varieties should not 

 be grafted on slow growing stocks. 

 The top will outgrow the stock and in 

 time may break off. The tree illustrated 

 measures five inches in diameter below 

 the graft and eight inches above. The 

 top in this case is not nearly so large 



Pewaukee Apple Grafted on Crab Stock 



as many others of the same variety ir 

 similar conditions. 



This tree is in the orchard of Mr. A. 

 E. Sherrington, of Walkerton, Ont. It 

 has been in bearing about fourteen years 

 and has produced yearly crops of first- 

 class fruit. 



Top-graft your apple trees in spring. 

 The best time is when the leaves are 

 pushing out. Wounds made then heal 

 quickly, and the scions are more apt to 

 live. If a large amount is to be done, 

 it is necessary to start earlier. 



