54 MISC. PUBLICATION 168, U. S. DEPT. OF AGRICULTURE 



Stigmonose (Insect Punctures) 



"Stigmonose" is a general name used to designate certain sur- 

 face depressions and distortions of fruit, conditions which may 

 be caused by a wide variety of insects, chiefly sucking ones of the 

 group which includes the plant bugs and aphids. Growth of the 

 flesh of the fruit at the point where the feeding punctures occur 

 is more or less retarded, and characteristic depressions form 

 (pi. 4, G). Underneath these depressions are often found small, 

 roughly hemispherical masses of corky brown tissue (pi. 4, H). 

 Badly affected fruits may be considerably distorted. The injury 

 to the flesh bears some resemblance to bitter pit. However, the 

 masses of cork 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. Stigmonose can occur anywhere on the sur- 

 face of the fruit, whereas bitter pit is usually confined to the 

 calyx half. 



An important cause of stigmonose in the Northwest and else- 

 where is the tarnished plant bug (Lygas oblineatus (Say)). The 

 bugs feed on apples, pears, and other fruits. On emerging from 

 hibernation in early spring, they feed on the buds, flowers, and 

 newly set fruits. Although most of the injured fruits drop, some 

 of them remain on the tree and may become very much distorted. 

 In the Northwest, injury is most common on Delicious apples 

 and on Anjou, Bosc, and Bartlett pears. Except for a brief period 

 in the spring, the bugs live on various herbaceous plants. Clean 

 culture helps to eliminate the favored plants on which the bugs 

 breed, but this cannot be recommended where cover crops are 

 considered essential to the orchard-management program. For 

 many years no satisfactory method of controlling the tarnished 

 plant bug was known. Recently several investigators obtained very 

 satisfactory control in peach orchards by spraying with DDT 

 just after the petals had fallen. Presumably such treatment would 

 be effective in protecting apples and pears from injury by this 

 pest. Exact timing of the applications, however, remains to be 

 worked out. 



In the northeastern part of the United States, apple red bugs 

 (Heterocordylus malinus Reut. and Lygidea mendax Reut.) are 

 responsible for a great deal of injury of the stigmonose type. 

 These bugs cause less distortion of the fruits than the tarnished 

 plant bug. The newly hatched red bugs, which appear on the 

 shoots of the apple trees about blooming time, can be controlled 

 by application of nicotine sulfate in either the pink or the calyx 

 spray, depending on the time when the insects first appear. 



The boxelder bug (Leptocoris trivittatus (Say)) also occasion- 

 ally causes stigmonose. Boxelder bugs, which are larger than 

 tarnished plant bugs and marked with red, feed in clusters on 

 maturing fruit. They breed chiefly on boxelder and when full- 

 grown migrate to nearby apple trees. Replacement of boxelder 

 trees in the vicinity of orchards with other kinds of shade trees 

 will prevent injury from this cause. 



The apple maggot, or railroad worm, may cause small dimple- 

 like spots in the surface of the apple, as described on page 9; 



