170 PRINCIPLES OF PLANT CULTURE 



to keep out these insects. Borers in the trunk can 

 often be destroyed by probing their holes with a flexible 

 twig. 



312. Leaf -miners often infest the leaves of various 

 plants. They may cause considerable injury by so de- 

 stroying the chlorophyll tissues as to interfere with normal 

 photosynthesis (58), and also by making leaves of spinach 

 and beets, grown for greens, unfit for use. These insects 

 are exceedingly difficult to control, since they feed by 

 tunneling between the two leaf surfaces, as indicated by 

 their name. The most satisfactory methods consist in 

 frequent cultivation during the time the pupa is in the 

 ground or burning the fallen leaves in those cases where 

 the insect pupates in them. 



313. The codlin-moth (Carpocapsa pomonella), which 

 causes so-called " wormy " apples and pears, is controlled 

 by spraying the trees with water containing paris green 

 (284) or arsenate of lead (286). The first spray should 

 be applied three to seven days after the petals (142) fall, 

 to be followed by a second about ten days later. Another 

 application is necessary in some states to control a second 

 brood of this insect. The time will vary in different states. 

 In Wisconsin July 15 to 30 is about the proper date, 

 depending upon the season. A drop of poisoned water 

 should be lodged in the calyx (141) of every fruit, and as 

 this evaporates, the poison deposited on the skin kills 

 the newly-hatched insect as it eats its way inward. 



A band of cloth or paper, placed about the trunk of 

 'fruiting apple or pear trees forms a convenient retreat 

 for larvae of the codlin-moth, in which to pupate. They 

 may then be readily destroyed by removing the band. 

 The bands should be a few inches wide, and should be 

 put on before midsummer. They should be taken off 



