﻿BULLETIN 1137, U. S. DEPARTMENT OF AGRICULT1 



wide and 2 reds long. On November 1 1. afti r the adult Hessian flies 

 had ceased to fly, determinations of the percentage of lly infesta- 

 tion were made in all the plats by W. B. Cartwrigh't, of the Bureau 

 of Entomology. In the early j>art of the following spring observa- 

 tions were made in the sam s plats by Dr. R. W. Webb, of the Bureau 

 of Plant Industry, to d termine the percentage of rosette infestation. 

 The results of these observations of infestation are given in Table 1. 



Table 1. — Infestations of Harvest Queen whi at by the Hessian fly in the foil 

 of 1920 and by rosette in the spring of /.''.'/ on plats near Granite City, III. 





Date of sowing. 



Plants showing infesta- 

 tion (per cent;. 





Hessian fly, 

 in the fall. 



ette, in 

 the spring. 





2.5 











93.6 





85. *i 





96. 









Since rosette develops very early in the spring, before the spring 

 emergence of the Hessian fly adults, it is obvious that any possible 

 connection between this insect and rosette can involve only the fall 

 infestation of the Hessian fly. It will be noted from Table 1 that 

 there is no direct correlation between the percentage- of fall Hessian 

 fly infestation in any of the plats and the percentage of rosette in 

 the same plats the following spring. The fall fly infestation was in- 

 significant or absent, while the percentages of rosette were very high. 

 It is therefore quite evident that some other factor than the Hessian 

 fly is the prime cause of wheat rosette. 



While all evidence indicates that the disease in question is not 

 caused by an insect, particularly the Hessian fly, it is recognized that 

 under certain conditions there is a possibility of confusing the symp- 

 toms of the disease with certain of those produced by the Hessian 

 fly, the wheat strawworm {Ilarmolita grandis Riley), and to a less 

 extent the wheat stem maggot (Meromtyza cemeripdna Fitch). It 

 therefore seems advisable to give the chief points of similarity and 

 difference between the symptoms of the maladies under discussion. 



The insects discussed in this paper have long been recognized as 

 important wheat pests, and details of their respective life histories 

 will not be included. Osborn (2) , 2 Webster (5), and many others 

 have recorded the life history of the Hessian fly. Phillips (J) has 

 given similar information concerning the wheat strawwqiprn, and 

 Webster (4) has discussed the life history of the wheat stem maggot. 



SYMPTOMS OF WHEAT ROSETTE. 



A complete description of the symptoms of wheat rosette lias been 

 given by the senior writer in another publication (1). 



FALL PERIOD. 



Field symptoms. — As this disease is interpreted at the p resent 

 time there are apparently no field symptoms in the fall. During 

 the past two seasons a highly susceptible variety of wheat growing 



2 Serial numbers (italic) in parentheses refer to "Literature cited" on page 8 of this 

 bulletin. 





