﻿4 BULLETIN 1137, U. S. DEPARTMENT OF AGRICULTURE. 



A little later in the spring an excessive number of tillers becomes 

 strikingly evident, giving the diseased plants a rosette appearance 

 (PL II, />). Later, the underground portion of the older tillers 

 develops a brown, rotted condition (PL I, C). 



SUMMER PERIOD. 



Field symptoms. — In case of badly infested wheat fields, those 

 plants which escape or resist rosette develop and form a thin 

 stand of grain, and the diseased plants under usual conditions slowly 

 recover by sending up straggling secondary tillers. In the case of 

 the early death of diseased plants, the thick tufts of plant remains 

 will be found on the ground usually until after harvest, except during 

 seasons of heavy rainfall, when these plants are practically all 

 washed away. 



Recovering diseased plants do not ripen until after the healthy 

 plants: hence, as the healthy plants turn in color at maturity the 

 diseased areas show up conspicuously as green spots in the ripening, 

 healthy grain. 



Plant symptoms. — In the case of diseased plants which do not re- 

 cover, their dead remains, consisting of low compact tufts of tillers 

 and leaves, will be found in place on the ground except where they 

 have been washed away. Plants which recover consist of a number 

 of straggling secondary culms coming up from the stool of dead fall 

 tillers and leaves. Such secondary culms may or may not produce 

 heads. In some cases remarkable recovery occurs, especially on rich 

 moist soil, but usually very small imperfectly filled heads develop. 

 Frequently, plants are found in which only part of the tillers are 

 diseased. In such cases the healthy tillers usually develop normally, 

 resulting in a plant consisting of a few normal tillers with dead 

 fall tillers at the base and perhaps a few secondary tillers attempting 

 to attain maturity. 



SYMPTOMS PRODUCED BY THE HESSIAN FLY. 



FALL PERIOD. 



Field symptoms. — A wheat field infested with the Hessian fly is of 

 a shade of green darker than normal, with a certain bristling appear- 

 ance due to the stiff and upright leaves of the infested plants. As 

 the season advances, the seemingly healthy appearance gives way 

 to a more or less ragged, sickly stage, described by the farmer as 

 " going back." 



Under certain conditions seemingly dependent upon the response 

 of the wheat plant to soil variations, there may be a decided field 

 spotting due to fly infestation. These spots or patches are usually 

 associated with such conditions as soil color, type, topography, and 

 exposure. 



Plant symptoms. — In the case of an infested plant, the central 

 shoot is usually absent, and the leaves are broad, short, more or less 

 stiff, and of a dark-green color (PL II, E). By stripping down the 

 leaf sheath, the larva or the puparium (flaxseed) can easily be found 

 near the base of the plant (PL III, E). The presence of a single 

 small larva or a flaxseed is sufficient to have caused the characteristic 

 appearance of the wheat plant. An infested plant may produce a 

 few normal tillers or it may be killed, depending upon the degree of 

 infestation. In the latter case, as the season advances the plant 



