Pests and Diseases of Plants 247 



made, of IS per cent strength, and replace the earth. Be sure you get 

 a good emulsion, for free oil is dangerous. For the insects above ground 

 on the twigs, a good spraying while the tree is out of leaf will kill 

 man3% but some will survive for summer spraying, and for this a tobacco 

 spray may be most convenient. 



Blister Mite on Walnuts. 



/ am sending you some walnut leaves with some swellings on them. 

 They are very plentiful on some trees here. Is the trouble serious and 

 will it spread? 



This is merely Erinose, or Blister Mite, which is a very common 

 trouble on walnuts, but does not do enough damage to call for methods 

 of control. These swellings are caused by numerous, very small insects 

 which live within the blisters on the under side of the leaf amongst a 

 felt-like, heavy growth which develops there. While this effect is very 

 common, it produces no appreciable injury and needs no treatment for 

 its control. 



Scale on Apricots, 



/ would like to know how to check the scale on apricot trees. 



The most common scale on apricots, the brown apricot scale, is 

 usually held in check by the comys fusca, which is as widely distributed 

 as the scale itself. If it gets beyond the parasite, you should spray in 

 w^inter with crude oil emulsion. If some scales are punctured or have 

 a black spot on top, the comys fusca is busy and you probably will be 

 safe enough without doing anything. 



Fumigating for Black Scale. 



/ would like to know the best method of eradicating the black scale 

 from my orange trees, whether by spraying or fumigation? 



Spraying has been given up as a suitable method for controlling the 

 black scale on citrus trees, and the only recognized method of merit where 

 the scale is bad is by fumigation with hydrocyanic acid gas. You should 

 communicate with your county horticultural commissioner, who, through 

 inspectors, will see that you have a good job done, at the right time 

 and at as moderate price as is compatible with good work. It is irn- 

 possible to 'eradicate' the black scale, but there is a great difference in 

 the amount that can be killed, and it pays to have a job done as near 

 perfectly as possible. Similar methods of attacking other scale insects 

 on citrus trees are used. 



Finding Thrips. 



Hozv can the presence of pear thrips be detected in a prune orchard? 

 Will the distillate emulsion-nicotine spray control brown scale as zvell 

 as thrips? 



You can find thrips by shaking a cluster of blossoms, as soon as they 

 open, over a sheet of paper or in the palm of your hand. The thrips are 

 very minute, transparent, somewhat louse-like insects. The spray you 

 mention would probably have little effect on the brown scale which would 



