- U. S. DEPAR I'MIA I' I )l AGRICULTURE BUREAU OF WTOMOLOQT CIRCULAR Ho. 154. L. O. HOWARD. Eniomologirt *nd Clurf of Burc»u. THE LEAF BLISTEB .MITK. A. L. QUAINTANCE, U V - 1 1 , BUREAU OF ENTOMOLOGY. L. O. Howabd, Entomologist and Chief of Bureau. C. L. Mablatt, Entomologist and Acting Chief in Absence of Chief. B. s. Clifton, Executive Issistant. W. F. Tastet, chief Clerk. F. II. Chittenden, in charge of truck crop andstqred product insect investigations. A. D. Hopkins, in charge of forest insect investigations. W. I>. IIixii u. in charge of -southern field crop insect investigations. F. M. Websteb, in charge of <■< n i:.\ a. I. iii \in i \m i . In Charge of Deciduous Fruit Insect Investigations. INTHODU" [TON. Leaf blister mites are among the smallest <>f animal forms which attack horticultural crops. These minute creatures, only one one- hundred-and-fiftieth of an inch in length, are invisible to the un- aided eye, and m> seen under a good hand lens appear a- the merest -peck. Although the mites themselves are probably unfamiliar to most ofchardists, their work is well known, to pear growers and apple growers, in the reddish or greenish pimples <>r blisterlike spots to Ik- noted in early spring on the young foliage of these plant-. Later these blisters become brown and dead, spotting and blotching the leaves, the injury resembling that due to leaf-spot fungi or from -I rays, with which injury, in fact, the work of this mite i- frequently confused. When the creatures are abundanl the foliage may be almost covered with the blisters or l.p.w n -pot-, and the usefulness of the leave- to the tree i- thus greatly impaired. Foliage severely injured will fall prematurely, retarding the development of the fruit and in extreme cases much id' the crop will fall to the ground. I S fig. 1.) The leaf blister mite i- not an insect, hut belongs to that class of animal- containing the spiders, scorpions, daddylonglegs, etc. and to the order Acarina, represented by such well-known form- a- the scah mite of sheep, the cattle tick, and the red spider. It- family, the Eriophyidae (Phytoptidse), contain- numerous species, all of which are plant feeders, attacking principally the hud- and lea Several members of the family are of much economic importance. ntie Landois infests vinifera varieties of grapes in por- 1 Z THK LEAF BLISTEB MITE. (ions of Europe and in California, producing the so-called " erinose " of the vine. Eriophyea padi Nalepa (=1?. prurd-crumena Walsh) is the cause of the nail-like galls sometimes found on the leaves of plum. (Typhlodrom/us) PhyUocoptea oleivorus Ashmead infests the fruit and foliage of the orange, producing a russeted condition. PhyUocoptea eomutus Banks feeds upon the upper surface of the leaves of the peach, so injuring them as to give the foliage a silvery sheen. PhyUocoptes sclilecldendali Xalepa occurs on the foliage of the apple, and in Montana very important injuries have been at- tributed to it. * [W^yr^^^SBl * "' »»- .'«v t*- •'-- ~"~ •*■ /-, U. -_._. fcjg s?@^ ?r -*- "^"-^t w 7 - . 1 $ *% w * / / ■ Fig. 1. — Apple leaves injured by the leaf blister mite (Brtophyea i>>hi). (Original.) ORIGIN AND DISTRIBUTION. The mite is not native to the United States and was probably in- troduced at an early period, presumably from Europe on nursery stock, buds, or scions. It was first recorded in the United States by Townend Glover, in 1872, and since that date has made its appear- ance in the principal pear-growing regions of the United States and Canada. It is known to occur in portions of Europe, in England. Russia, and Tasmania, and is probably present in other fruit-growing regions of the world, being at the present time a truly cosmopolitan pest. i 111 ii \i 1:1.1-- 1 11; Miii. CHAHA< 111: IJ] INJURE \ M> DESTRl't I l\ 1 \ I --. The mile-. pass the winter on the trees, under the bud scales, and attack ilic leaves as soon a- these begin to «push oul in the Bpring. They bore -mall hole-, from the underside t" the interior '»f the leaf, where they deposit their eggs, and with their progeny feed upon tin' tender cells of tin 1 leaf substance. Their activities within tin- leaf tissues very quickly resull in the developmen! of galls or swellii These an- at (i 1-- 1 -mall, pimple like eruptions, especially evident on the upper surface of young leaves, whitish in color on the apple, but usually with a reddish t inge on the pear. The spots increase in size, the largest be- coming a- much as one-eighth of an inch in diameter. On pear leave- the -pot-, as a rule, be- come re.I. often brilliantly col- ored a- they grow, whereas on apple this reddish coloring i- ab- sent or faint. ( )n the underside of the leaf the oralis are whitish and blisterlike, not differing much from the general color of the leaf surface. Later they turn brownish or black, due to the death of the injured leaf cell-, lo-e much of their thickness, and some may become somi what shrunken. Figure 2 illus- trates a gall on pear leaf a- seen in cross-section, the normal structure being shown at //..• <> i- tin' opening to the interior of the gall and < designates eggs of the mite. A cro — ection of one of the dried-up galls i- shown in figure 3. i"i.. 2 1 :if null. In cr oss section, of leaf blister mlti nlng ->f sail : ■ • if miii'; 11. normal itruclure of leaf. 1 a ft it Boraner | Fig. ". — SectloD of leaf, showing structure of gall of ''l i-t.-r mite In autumn: <;. OaU; o. opening of gall' (After Comstock.) On pear, the galls occur more along each side of the midrib of the leaf and on apple at the base of, and along the margins of the leaf. When numerous, however, the spots will merge together, forming large patches or hands of variable size, often involving most of the leaf. When thus abundant the leaves may become more or less rup- tured and wrinkled, and in the case of the apple the margins may curl up. showing the underside. Leaves badly infested are likely to fall prematurely, resulting al-o in the dropping of the fruit from clusters with wor-t injured foliage. The fruit and fruit --tenis of both apple and pear are al-o attacked, the light-colored pimple- 4 THE LEAF BUSTER MITE. occurring mostly around the calyx end of the fruit and resulting in no material injury. The injury to the fruit-stems is noticeable as irregular thickenings, and when severe may cause some of the fruit to fall, although loss frofn this source, even in worst infested orchards, will not be great. FOOD PLANTS. Pear and apple are the more common food plants of the blister mite, though other plants are attacked. Dr. Nalepa records this species from foliage on the white lx»am tree (Sorljus aria Crantz). the European mountain ash (Sorhux niii-ujmria L.). the wild-service tree (Sorbus torrninalis Crantz), the service berry (Amelanchier vulgaris Monch.), and the common cotoneaster (Cotoneaster vulgaris Lindl.). According to Parrott the mites have been found on over 250 vari- eties of apples, injury being severe on some well-known commercial sorts, as Ben Davis. King, Baldwin, Rhode Island Greening, and at the agricultural experiment station at Geneva, X. Y.. the \Villiams Favorite was noted to be especially subject to attack, the trees having been prematurely defoliated for two successive seasons. DESCRIPTION AND HABITS. The general appearance of the blister mite is shown in figure 4 in dorsal and ventral views. The mite is microscopic in size, measuring on the average about one one-hundred-and-fiftieth inch in length, whitish in color, a few individuals pinkish. The abdomen slopes gradually toward the posterior end and is numerously ringed. There are only two pairs of legs, and these and the body bear setae, which from their character and location are of importance in the deter- mination of species in this group, as are also the number and charac- ter of rings on the abdomen. The young, except in size, bear a gen- eral likeness to the adults, and the eggs, though proportionately large as compared in size with the parent, are only 46 microns through the greater diameter. These are whitish, translucent, with rounded ends, and are deposited in the interior of the galls (see fig. 2). The resulting larvae feed upon the cellular leaf substance, working out in various directions, though they are not especially active. The mites are to be found on the foliage from their appearance in spring until fall, and several generations are evidently produced in a season. Hibernation occurs under the bud scales, the mites often congregating in colonies of 50 or more. They become active in the spring often before the buds burst, congregating around the base of hud scales, where they feed, many molting at this time. "With the bursting of the buds and the pushing out of the tender leaves, these are attacked and the characteristic blisterlike spots soon develop. I ill i.l \r BLIS III: MM E. Notwithstanding the minute size of these creatures, they fall prey in considerable numbers, as observed by Prof. Parrotl in Nev "> nrl, State, to the attack of a mite ' N - itu pomi Parrotl i which he thinks materially assists in reducing their numbers. M I i Hi >n> {)] CONTHOI The leaf blister mite will yield to thorough treatment with kero- sene emulsion, miscible oils, i>r Lime-sulphur washes. The d er mite [BHophj/m pyri) : i. Dona] vi.'w: _•. rentral rlew. QreaUj enlarged i After Nal< p these sprays, as for the Sun Jose scale, should also protect orchards from important injury from the mites. When it -;irv to spray for the mites alone, and in cases of severe infestation, as has been notfil in apple orchards in New York State, two treatments have been recommended l>y Parrott, using standard kerosene emul- sion diluted with ."» parts of water. One application should be given in late fall as soon as most of the leave- have fallen and another the following spring before the trees put out foliage. If lM>th the fall and spring application- are uot practicable, the preference should be UNIVERSITY OF FLORIDA b Tin: LEA* blister 1 3 1262 09216 5959 given to fall treatment. At this time many of the mites have not yel gQne to the bud scales, hut occur in the pubescence of the young wood and are hence more easily killed. Lime-sulphur washes arc excellent treatment- for these mites and their employment is perhaps preferable as avoiding danger of injury to fruit buds by the oil sprays. If a lime-sulphur wash is employed, it should be applied with great thoroughness, completely coating the tree so thai when spraying is finished the tree will appear as if whitewashed. The homemade wash, according to the old formula, lime 20 pounds, sulphur 15 pounds, and water to make 50 galL will be quite effective; or the homemade or commercial concentrate may he used. The former may be made according to the formula. lime 50 pounds, sulphur LOO pounds, and water to make 50 gallon-. When thus prepared the concentrate should be used at the rate of one part to 9 or 10 parts of water. Applications of these washes may also be made in the fall as described for kerosene emulsion and in the spring, and if only one treatment is to he given the spring appli- cation is preferable, as it takes the place of the first application of a fungicide for apple scab. When the mite is quite troublesome both fall and spring treatments would insure its control more quickly and completely. On the pear the mites may be kept reduced to an important extent simply by searching out in the spring branches bearing worst infested leaves, pruning these oil' and burning them, or sprays may be em- ployed exactly as indicated for the apple, if this is considered necessary. Except in cases of serious infestation special spraying for the Mister mite will not be necessary. As to whether or not it i- advisa- ble to spray, the orchardists will have to decide after determining as exactly as is possible the amount of injury being done by the mites, and care should be taken not to confound with it- injury that which has resulted from fungicidal or Paris-green sprays, and from leaf- spot (li-ease-. Approved : James Wilson, Secrt tary of . Vgriculture. Washington, I). C, April /<>. 1912. ADDITIONAL COPIES of this publication XV may be procured from the SUPERINTEND- ENT of Documents, Government Printing Office, Washington, D. C. , at ."> cents per copy