MABKET DISEASES OF APPLES, PEARS, QUIKCES 47 



Sulphur injury, from either lime sulphur or other sulphur fungi- 

 cides, is likely to be worse under high-temperature conditions. Mild 

 cases often take the form of a bronzing or browning of the area 

 most exposed to the sun, whereas severe injury may be exhibited by 

 the formation of hard leathery areas which may or may not slough 

 off (pi. 7, B). The Grimes Golden and Golden Delicious varieties 

 are especially susceptible to injury by lime-sulphur sprays. 



In addition to russeting, arsenicals are responsible for another 

 form of injury to the fruit known as calyx injury or blossom-end 

 injury. This appears as a dark-brown or nearly black area around 

 the calyx of the apple, and often furnishes a place of entry for the 

 black-rot fungus or other decay organisms. 



Oil sprays cause various types of injury on apple fruits. One of 

 the most common forms is very similar to the calyx injury that re- 

 sults from arsenical sprays. In other cases oil injury is exhibited 

 by russeting and deformation of the apple, which becomes gnarled 

 and roughened. Injury from oil sprays is much more likely to occur 

 on trees suffering from drought or on those low in vigor from other 

 causes. Spraying should be avoided during periods of high tempera- 

 ture (90° F. or above), and care must be exercised at all times to 

 use an acceptable type of oil as well as to have it properly emulsified. 

 {S3, 56, 63, 80, 102, 103, 136, 11^8, 161, %1.) 



STIGMONOSE 



INSECT PUNCTURES 



Stigmonose is a general term used to designate a dimpling and 

 distortion of the fruit, a condition which may be caused by a wide 

 variety of insects, chiefly the sucking insects in the group which 

 includes the plant bugs and aphids. The growth of the flesh of the 

 fruit at the point where the feeding punctures occur is more or 

 less retarded, forming characteristic dimples (pi. 19, D). Under- 

 neath these dimples will often be found small, roughly hemispherical 

 masses of corky brown tissue (pi. 19, C). Badly affected fruits may 

 be considerably distorted. The injury to the flesh bears some resem- 

 blance to bitter pit but can usually be distinguished from it by the 

 fact that the brown masses underneath the spots are generally darker 

 brown and larger than those found in bitter pit. Furthermore, they 

 are always near the surface, whereas bitter-pit spots may be either 

 near the surface or deep within the flesh and in either case are closely 

 connected with the water-conducting system of the apple. The 

 claim has been made that pears affected with plant-bug stigmonose 

 do not keep well in storage, but there is no experimental evidence 

 that this claim is well founded. 



An important cause of stigmonose in the Northwest and elsewhere 

 is the tarnished plant bug {Lygus prateriMs L.). Besides attacking 

 apples, the bugs feed on pears, peaches, and other fruits. On emerg- 

 ing from hibernation in early spring, the bugs feed on the buds, 

 flowers, and newly set fruit. * Although most of the injured fruit 

 drops, a certain proportion remains on the tree, and may be very 

 much distorted. In the Northwest, injury is most common on 

 Delicious apples, and on Anjou, Bosc, and Bartlett pears. No 



