HESSIAN FLY 139 



Scab. Wheat scab is a mold (Fusarium) that affects the wheat 

 head. Only a part or all of the head may be affected. It will be rec- 

 ognized by the reddish spot at the base of the affected glumes. There 

 is no known remedy, but it is best to get clean seed and not use seed 

 from an infected field. 



Insect Enemies. All wheat insect enemies are quite irregular 

 in their attacks. This seems to be due, in turn, to the enemies of the 

 insects that keep them more or less controlled. The " green bug/' a 

 plant louse, is a good example. This insect is to be found on 

 wheat every year, but is seldom injurious, as its natural insect enemies 

 are usually so plentiful that it is kept in subjection. Occasionally, 

 however, the enemies are outdistanced and the green bug increases at 

 an enormous rate, often doing great damage for a season. Weather, 

 also, favors or hinders insects, and it is only when we have a com- 

 bination of favorable conditions that they are usually very 

 destructive. 



The principal insects are (1) Hessian fly, (2) chinch bug, (3) 

 green bug or plant louse, and (4) wheat midge. Of these the Hes- 

 sian fly and chinch bug are favored by dry weather and the wheat 

 midge by moist weather. 



Hessian Fly. The Hessian fly is a small two-winged insect. In 

 most of the winter wheat belt it produces two broods a year, the first 

 in August and September and the second during May and June, 

 being earlier South. The fall brood lays eggs on the leaves of the 

 new fall-sown wheat. In three to ten days, depending on the 

 weather, the eggs hatch and a small worm or larva emerges. The 

 larva attacks the plant just below the surface of the ground. A 

 single larva will injure a plant and three or four may kill it. The 

 damage is somewhat regulated by the vigor of the wheat. The 

 larva soon goes into the pupa or " flax seed " stage, when it looks 

 like a small, brown flax seed attached to the stem under the first 

 leaf sheath. It remains in this state until the following May when 

 the second brood is hatched. 



Frost will kill either the insect or its eggs, and it can be controlled 

 by late planting. If planting can be regulated to come about two 

 weeks before the first frost, there will be little danger from the fly. 



