REMEDIAL MEASURES I CULTURAL METHODS. 35 
When we consider the carnivorous habit and observe the immense 
numbers of spiders in the fields, and realize that in many cases leaf- 
hoppers are the most abundant and accessible food supply for them, 
it is easy to credit the spiders with immense service in this direction. 
REMEDIAL MEASURES. 
The various methods of control for leafhoppers may be discussed 
under the general head of remedial measures. Some of the par- 
ticular modes of treatment, applicable to certain species and to 
particular conditions of culture, must be discussed in connection 
with the species concerned. Practically all of the measures avail- 
able must be adapted for the seasons or conditions of crop and conse- 
quently to advise any general method, applicable in all cases, is 
impossible. 
CULTURAL METHODS. 
Under the head of cultural methods we may discuss the effect of 
different plans of cropping, or the rotation or alternation of different 
crops, and this is, in many cases, one of the most effective means in 
keeping leafhoppers in check. The general immunity of spring 
wheat, in the northwestern wheat-growing regions, is quite certainly 
due to the effect of the methods of culture prevailing there, which do 
not permit a general infestation of the wheat fields; as, during the 
time when the insects would scatter for the deposition of eggs, the 
fields to be planted in wheat are mostly bare and furnish no attraction 
for the insects. In the case of the northern wheat regions, as in Penn- 
sylvania, another condition is evidently to be considered and this is 
extreme cleanliness of the culture, the fields being cultivated so close to 
the fences that scarcely any grassland remains, as is the case generally 
where the dispersal of the leafhoppers occurs. Another very evident 
condition is the accumulation of hoppers in fields which have been 
continually in grass for a number of years. In such cases they 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 only one or two years it appears quite evident that rota- 
tion tends to eliminate the leafhoppers and that it requires two 
or three years of continuous grass to give opportunity to the leaf- 
hoppers to reach their full numbers. In sections where there is a 
general plan of rotation so that grass occupies certain 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 North Dakota Agricultural College farm (see PL II, fig. 1), where 
a pasture in brome grass (PI. I, fig. 2) for several years was badly 
infested, while nearby 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 in any control to be secured* 
