INSECTS INJURIOUS TO BEETS AND SPINACH I29 



necessary to employ remedies, as these creatures are peculiarly 

 susceptible to atmospheric conditions, doing their greatest in- 

 jury in cool, damp weather, and being held in nearly complete 

 abeyance at times by numerous natural enemies which flourish 

 in dry and even hot weather, as is very well known. In 

 gardens of table beets, kerosene emulsion, pyrethrum and fu- 

 migation, according to directions given on page 165, are of value. 

 Practically none of these remedies can be employed on large 

 fields, but are useful in small ones. Clean farming and fall 

 plowing are always advisable, and crop rotation should be prac- 

 ticed where possible with potatoes or similar crop. 



Two species of root-aphides do great damage. They are the 

 beet aphis and beet root-aphis. 



The Beet Aphis (Pemphigus betce Doane) ruined in one year 

 in a single valley upwards of 1,000 tons of beets. This. was in 

 Oregon. The species also inhabits Washington, and probably 

 California, and it is probable that it may be reckoned among 

 the important beet pests of the future. 



Owing to the large acreage in sugar-beet growing regions of 

 the United States we cannot successfully control the root-aphides 

 by means of insecticides. It would be supposed naturally that 

 heavy flooding and plowing in fall so as to expose the insects 

 to the frost might control it, but this is sometimes a failure. 

 Our knowledge of alternate food plants is somewhat limited, 

 but we can recommend the avoidance of beet cultivation in land 

 where other plants subject to the attack of this insect have 

 grown; also crop rotation. If the aphides are found at work 

 only in parts of a field, they could be destroyed here with 

 kerosene emulsion applied preferably just before rainfall, or by 

 following the application with a flooding of water. 



Root-aphides are almost invariably associated with ants, 

 which foster them and act as distributers of infestation by car- 

 rying wingless forms from plant to plant. It is therefore ad- 

 visable to break up the nests of ants as fast as they are found. 



