﻿SYMPTOMS OF WHEAT ROSE'! t 



SYMPTOMS CAUSED BY THE WHEAT STEM MAGGOT. 



FALL PERIOD. 



Field symptoms. — A field infested by the wheat stem maggot has 

 very much the same appearance as if infested by the Hessian fly. 

 The stem maggot is not usually so prevalent as the fly, and in- 

 stances of extreme infestation are more rare. The color of an in- 

 fested field is a darker green than normal, and when severely in- 

 fested the ragged, sickly appearance comes on earlier than if in- 

 fested by the Hessian fly. 



Plant symptoms. — An infested plant has the center shoot dis- 

 colored or dead and the other leaves broader and darker green 

 than normal. The larva, difficult to find when small, occurs at the 

 base of the stem, where it lacerates the tender tissues with its mouth 

 hooks and feeds upon the juices. 



SPRING PERIOD. 



Field symptoms. — Depending upon the severity of the infestation, 

 gaps in the drill row caused by the dead plants mark a field infested 

 by the wheat stem maggot in spring; but there are so many other 

 causes of this same appearance that it can not be taken as charac- 

 teristic of this insect. 



Plant symptoms. — The infested culms, and frequently the entire 

 plant, if able to withstand the injury during the fall, usually die 

 during the winter. Therefore, in the spring these dead and more or 

 less disintegrated plants contain the full-grown larvae or pupae of 

 the insect (PL IV, B). 



COMPARISON BETWEEN THE SYMPTOMS OF WHEAT ROSETTE AND 

 THOSE CAUSED BY THE WHEAT STEM MAGGOT. 



As in the case of the fall infestation of the Hessian fly, the symp- 

 toms produced by an infestation of wheat stem maggot in the autumn 

 will not lead to confusion with rosette, even though the plants 

 affected by the two maladies resemble each other in certain respects. 

 There is practically no chance for confusing the troubles in the 

 spring, because the spring infestation of the maggot does not cause 

 symptoms which resemble the fall symptoms in any way. 



CONCLUSIONS. 



The insect injuries described in this bulletin may usually be 

 diagnosed with certainty, on account of the presence in some stage 

 of the insect on the affected plant. However, in the late stages of 

 these disorders it is sometimes difficult to find any trace of the insect, 

 and in such cases the infested fields and affected plants are difficult 

 or impossible to distinguish from fields and plants affected by rosette. 



The symptoms of rosette can not be distinguished with certainty 

 after the spring period, and it is safer not to diagnose the disease 

 positively after early spring, especially if heavy rains have washed 

 out many diseased plants. 



In the early spring the disease manifests itself by a retarded 

 development of the plants, followed by excessive tillering and a dark 

 blue-green coloration, the leaves being broad and stiff and the whole 

 plant having a bunchy rosette appearance. At this time, when the 

 disease is not complicated with insect infestations the drill rows do 

 not have any blank spaces. 



