LEAF HOPPERS INJURIOUS TO CEREAL AND FORAGE CROPS 11 



pers occur in immense numbers, even as high as a million or more 

 to an acre, and the resulting injuries become serious. Contrasting 

 this with fields in grass for only one or two years, it appears quite 

 evident that rotation tends to eliminate the leaf hoppers and that it 

 requires two or three years of continuous grass to give opportunity 

 to the leaf hoppers to reach their greatest abundance. In sections 

 where there is a general plan of rotation in which grass occupies cer- 

 tain fields for not more than one or two years, injuries are restricted 

 to such an extent that they may be ignored. A striking instance of 

 this was noticed on the farm of the North Dakota Agricultural Col- 

 lege, where a pasture that had been in bromegrass for several years 

 was badly infested, while near-by fields recently planted in grass 

 were nearly free. When permanent pastures are in woodland, where 

 rotation is obviously impracticable, it is evident that other measures 

 must be adopted if control is to be secured. 



The possible control of the species by the cutting of the grass de- 

 pends upon an adjustment of the mowing to about the time when the 

 insect is present in the egg stage or in such an immature condition 

 that it is unable to migrate from the fields. At such times close 

 mowing of the grass will remove such eggs as may be included in 

 the leaves or stems and by exposing the young nymphs to a shortage 

 of food as well as to the direct action of the sun serve very materially 

 in bringing about their reduction. A somewhat similar effect may 

 be produced by the very close grazing of the grasslands during a 

 certain period, arranged if possible to correspond with that of the 

 egg deposition of the more common species, followed by a period of 

 absence of stock from the field so that the grass may have a period 

 of rapid growth. 



BURNING DRY GRASS 



Undoubtedly one of the most effective means of destroying the 

 eggs of the leaf hoppers in the fall or early spring is the burning of 

 the dead grass wherever this measure is practicable, and it may be 

 resorted to with the assurance that much will be accomplished. The 

 difficulty in this treatment arises from the fact that some grasses 

 will not withstand burning except when the ground is frozen or so 

 wet that the heat will not penetrate the surface, and that in cases 

 where fields are freshly seeded to grass the young plants may be 

 injured by this treatment. This process is, perhaps, most applicable 

 in the prairie regions, where the accumulation of dry material at the 

 surface of the ground furnishes abundant opportunities for the use 

 of fire, which will destroy the eggs and hibernating forms occurring 

 in the locality. It is also especially applicable to the alternating 

 strips of grass, in the localities where wheat and grass are planted 

 side by side. Direct observations of this method have revealed some 

 good results, but it has not been generally used under conditions 

 allowing for accurate measurement. In the prairie regions, before 

 general settlement, prairie fires were of very common occurrence, 

 and although it can not be determined just how much they have 

 accomplished in the control of these insects, it is worthy of note that 

 pasturage on these plains was of a very excellent quality and of long 

 duration. One of the most positive evidences of the effectiveness of 

 burning was observed in Ottawa County, Kans., on a level tract of 

 grassland adjacent to a stream, where part of the surface which had 



