62 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
TasBLe III.—Experiments with fall and winter plowing for the pear thrips in two 
orchards in the Santa Clara Valley, California—Continued. 
HUME ORCHARD. 
| Plowed and cross plowed. Not treated. 
| | 
Cage VII. | Cage VIII. Cage IX. Cage X. 
—_- ate Teese ee | : 
Total number Ohthrnips: <2 -n-)--s ees eee 421 643 2,185 1,771 
Total number of thrips per square foot of surface. 210 321 1,092 | 885 
Average number of thrips per cage: 
(GRC taA A 0 AY oo IGA 0D PS Sees Both Sane ROE SOConSD ae OOe cob oN ce BErEbe Cons Sagskescess 265 
Cages LX and) Xi ssi on dewcenees eRe oe eee ei on ane ARS AC eA acme ocides Ioscc ec 988 
Average number of thrips per square foot of surface in each cage: 
Wino: 172 0 ee eae Ree re te eine aan ee ea aoe cP ren arao oc boSorecmormsobscoto adh aeiic 133 
[Opin gc: c's ler ene aR Ee ae ee Sore BES ae Sec aa Se oet ns Aa ae EO Dias OAS eROEe ees 494 
Percentage living in treated areas as against the numbers of thrips in untreated ground............- 27 
Approximate percentage Ile = 5.5 aio stete ora cnte win a wheal nem fate amie ale ale i elation meals 7 
Bearing in mind that the larve penetrate into the ground quickly 
after they leave the trees; that they remain usually below the loose 
top soil, going deeper if disturbed, and also that they are most sus- 
ceptible to injury in the pupal stage, cultivating and plowing should 
be so arranged as to take best advantage of their habits, to encourage 
their locating near the surface, planning at the same time to reach 
them by late fall and early winter plowing. 
The principle of fall plowing is to use a moldboard or disk plow, 
and by turning the land over to bring the thrips which rest in the 
lower strata of ground up to the surface. The land should then be 
thoroughly harrowed or worked over with a disk cultivator. With 
the present methods of plowing, a strip of 2 feet or more of undis- 
turbed ground is usually left in the tree row. It is necessary also to 
plow to a less depth close under the trees than in the middle of the 
rows. The land should therefore be plowed and cross plowed, to 
insure breaking up all of the ground to a uniform depth, and harrowed 
after each plowing, to make the treatment thorough. 
The Landon orchard was uniformly plowed to a depth of about 9 
inches. It will be seen by referring to Table II that 81 per cent of 
all the thrips were above this depth and were therefore disturbed. 
Table III shows that there were 70 per cent less live thrips in ground 
which had been plowed and cultivated than in that which had 
received no winter treatment. These thrips, about 89 per cent of 
all which were disturbed, must therefore have been killed by the 
cultivating. 
The Hume orchard was plowed uniformly to a depth of about 7 
inches. Table II shows that 88 per cent of the thrips were between 
the surface and this depth, and Table III shows that about 73 per 
cent of the total number of thrips in this orchard were killed by 
cultivation. 
