THE PEAK THEIPS AND ITS CONTROL. 63 



Plowing during February and March, when adult thrips are coming 

 out of the ground, is not practicable because of the usually heavy 

 rainfall at this time, and because the ground breaks up into large 

 instead of small clods, for which reason only a few thrips are killed. 

 Then, too, plowing at this time seems to let the thrips out all at once, 

 thus increasing rather than reducing their injury. Several orchards 

 that have been kept under constant observation, which were plowed 

 during February and early March, were very much more seriously 

 injured than orchards of the same variety of fruit immediately 

 adjoining which were not plowed at this time. 



The benefits of plowing and cross plowing have been so evident 

 in every one of the several orchards treated that during the spring 

 one could tell almost to a row, by the healthful condition of the trees, 

 where the plowing began and where it ceased. 



A careful examination of the soil under prune trees, after plowing 

 had been accomplished, showed that almost no thrips were present 

 until a depth was reached where the plows had not cut. Below 

 this point the usual numbers of thrips were found. 



SPRAYING. 



Spraying for thrips has proved wonderfully successful wherever 

 proper sprays have been used and the work done with care and 

 thoroughness, while indifferent and careless work or improper sprays 

 are absolutely ineffective. The thrips must first of all be reached. 

 This necessitates high pressure — 125 to 180 pounds — and a rather 

 coarse, penetrating spray. It is necessary also that the spray be 

 directed downward into the buds, and not thrown at them from 

 below or from the sides. It should be remembered that spraying is 

 done, not to drive the insects away or to protect the tree from any 

 possible future attack, but to kill those insects which are actually 

 present on the trees. It may not be possible to reach all of the 

 thrips which are concealed in the buds even with most careful spray- 

 ing, but a very large percentage of them can be killed. Spraying 

 into partly opened buds and blossoms theoretically seems impos- 

 sible, but is found entirely practicable when a coarse, forceful spray 

 is thrown down directly against the tips. A tower platform should 

 be built over the spray wagon so that the tops of large trees can be 

 properly sprayed. 



Almost all of the standard spray formulas have been thoroughly 

 tested, and all except two have been ehminated. The bodies of 

 the thrips, both adults and larvae, are decidedly oily and strongly 

 resistant to all sprays which do not readily assimilate the oil. For 

 example, the lime-sulphur solution, which is very caustic, may be 

 thrown onto the thrips, and it will merely gather in globules on their 



