THE CLOVER ROOT BORER 4l 
FIELD OBSERVATIONS 
Observations were made on clover fields plowed in December, Jan- 
uary, February, and March in various parts of the Willamette Val- 
ley. Inall these cases root borers were found alive on buried roots 
up to the time of the spring flight, and in some cases there was only a 
small percentage of mortality among the beetles in roots not buried by 
the plow. In April and May great numbers of beetles were ob- 
served migrating from some of these fields. 
A field of old clover on creek-bottom land was plowed August 31, 
1920. Rainy weather began September 1, and there was an unusual 
amount of precipitation throughout the late summer, fall, and win- 
ter. On February 26, 1921, a few living root borers were found on 
roots fully exposed on the surface of the ground. Many dead bor- 
ers were also found, a large proportion of them showing a fungous 
rowth. 
5 A field which had been seeded in June, 1914, was turned under for 
green manure, without harrowing, about June 4, 1915. Most of the 
roots were completely upended and buried, except for their tips. On 
June 26 the roots were still infested by borers, there being present 
adults, larve, and eggs. Several adults were found which had been 
killed by fungus. Ten months after plowing, on April 4, 1916, liv- 
ing adults, which must have matured from eggs laid on the turned- 
under clover roots, were found on the moist, rotting crowns of 
buried roots, although many of the clover roots had completely rotted 
away. 
Part of a field was plowed and harrowed in late June or early July, 
1915. On August 13, the roots on the surface of the ground were hard 
and dry and on them were many dead borers, but none living. On 
October 7 no living borers in any form were found on the roots. 
Remains of larve and pupz were found dried up in their mines, 
and new adults were found dead and imprisoned in groups in 
the centers of the dried roots, which were so hard as to turn the edge 
of a knife. Now and then a beetle had died after forming an opening 
to the exterior, but one not large enough to permit emergence. The 
roots had dried so rapidly that the beetles were unable to gnaw their 
way out before death overtook them. 
A study of these data indicates that where clover sod is plowed 
and the roots harrowed out in the period between June 15 and Au- 
cust 1, a large percentage of the borers are killed, provided the weather 
is hot and dry after the plowing. Borers on roots that are deeply 
buried by this treatment often survive, so that complete extermi- 
nation in a field is rarely if ever possible. No experiments were 
performed in an irrigated region, but the writer is convinced that 
summer plowing of clover and subsequent withholding of irrigation 
water would be very effective under irrigation conditions. 
The data presented also show that the percentage of mortality 
among the borers is increased by plowing in late summer and early fall, 
because of the exposure of the borers to an unfavorable environment 
on the plowed-up roots. A disturbance of the normal activities of 
the clover root borers in the fall and early spring also results from 
this treatment, and undoubtedly interferes with the propagation of 
the pest in the following season. Unsuccessful attempts to secure 
offspring in cages started too early in 1919 (three weeks before the 
