49 BULLETIN 1426, U. S. DEPARTMENT OF AGRICULTURE 
first flight) showed that root borers, even when partially protected 
in a cheesecloth cage, are adversely affected above ground by rigorous 
weather in early spring. Considering the normally low rate of repro- 
duction in this species, it is probable that a regular practice of early 
fall plowing in badly infested localities would progressively diminish 
the amount of infestation and eventually reduce the numbers of the 
pest to such an extent that little damage would occur to clover in 
the first crop year. [all plowing would probably be especially effec- 
tive in an irrigated region where the winter rainfall is light. 
The data show that late fall or winter plowing has little effect as 
a control measure for the clover root borer. They also show and 
field observations very strongly emphasize, as Webster (46) and 
Davis (9, p. 46) have noted, that spring plowing of clover is absolutely 
ineffective in the control of the species, and may be a most harmful 
piactice in the case of heavily infested fields. Such spring plowing 
causes the mature adults to leave the field almost simultaneously, 
Fic. 14 —View of second-year clover field, showing weedy places where clover has been killed out by 
the root borer 
and they may afterwards settle on any new clover in the vicinity in 
such numbers that the simultaneous attack of many borers will very 
seriously injure or utterly destroy it early in the season. 
The practice of green manuring, at least under conditions prevail- 
ing in western Oregon, is shown to have little restraining effect on the 
clover root borer. Some of the insects are able to mature, even from 
egos on clover roots which have been turned under. The only practi- 
cable way of killing root borers is by the drying and hardening of the 
roots; and in western Oregon this is possible only by harrowing out 
the roots in the summer or early in the fall of a dry season. 
In some localities in western Oregon where the ranchers still attempt 
to follow the practice of maintaining clover fields for three or more 
years, root borers have for some time been extremely destructive. 
In other localities, where a one-crop system of clover culture is prac-_ 
ticed, the insect has been appreciably reduced in numbers and no 
