THE CLOVER ROOT BORER 43 
longer occasions serious loss. The writer, after studying this problem 
in all its phases, is convinced that the early practice of allowing clover ~ 
to stand over a considerable period is responsible for the tremendous 
increase of the insects in recent years in western Oregon (fig. 14). 
This opinion seems to gain some support from the apparent reduction 
in numbers of these insects since the reduction in the acreage of 
clover and the adoption of a short clover rotation, both brought 
about in many localities by war-time conditions. 
A farm practice (23, p. 5) that has proved very successful in parts 
of Yamhill County, Oreg., especially on the lighter soils, is the seeding 
of clover either alone or with rape, in May or June, on well-prepared 
ground, and the subsequent pasturing of the clover during the late 
summer and fall of thesame year and until about June 1 of the following 
year. Thestock are then taken off and a seed crop obtained. Usu- 
ally the clover is subsequently plowed up and seeded to grain, 
although occasionally it is maintained for another year. This prac- 
tice, where generally followed, has reduced damage by the root 
borer and has also practically eliminated damage to the seed crop by 
the clover flower midge and the clover seed chalcid. The practice 
could be improved upon by less close pasturing during the year of 
seeding. It may happen that thé clover is pastured so closely that 
the roots are kept small (40, p. 91) and therefore are injured more 
severely by a few root borers and clover root curculios (Sitona hispid- 
ulus Fab.) than if they had made a larger, more vigorous growth. 
The practice of cutting the first crop of clover early for hay, as rec- 
ommended for the control of the clover flower midge, would also tend 
to reduce injury to the seed crop by the clover root borers, as, except 
in case of an unusually heavy infestation, the clover seed would mature 
before any large number of clover plants would be killed by their work. 
There are many good reasons why clover should not be left undis- 
turbed for a number of years. Not only does such treatment per- 
mit the increase of root borers, but all kinds of clover insects multiply 
rapidly in old fields, especially root curculios, clover leaf weevils, cut- 
worms, grasshoppers, leafhoppers, plant bugs, and aphids. Young 
clover, seeded into the following year’s wheat crop, is often severely 
injured by some of these insects when it has been preceded by clover 
sod of some years’ standing. Vetch sown on old clover sod is often 
more or less severely injured by clover root borers and curculios. Old 
clover fields in western Oregon also become breeding places for ro- 
dents, which are often destructive to clover and other crops. Figure 
15 illustrates the damage in a clover field in its second crop year by 
root borers, grasshoppers, and rodents. 
FERTILIZER 
Davis (9, p. 46) experimented with large quantities of commercial 
fertilizer as a possible repellent for the clover root borer, finding that 
such heavy applications had no apparent effect on the root borers 
but often severely injured the clover. 
The writer tried applications of phosphatic fertilizers to clover, 
hoping to induce more rapid root growth. The plots of experiments 
at Corvallis, Oreg., conducted by the Bureau of Plant Industry in 
cooperation with the Oregon Agricultural Experiment Station, were 
also available for study. From these sources no definite conclusions 
