INSECTS AND DISEASES 101 



Spores may be produced by some of the diseases as frequently 

 as every ten days. 



Neither the details of spraying nor Hsts of diseases and 

 insects can be described in this book, but the reader will find 

 the information in books and bulletins on the subject. In- 

 sects may be divided into two general groups, those that 

 chew or eat the leaves, and those that suck the juices from 

 the plant. The first group can be killed by spraying the 

 leaves with a stomach poison, such as the various compounds 

 of arsenic, including Paris green, compounds of lead, helle- 

 bore powder, and pyrethrum. The last two are gaining in 

 popularity because they are less dangerous for animals. The 

 sucking insects must be killed by spraying the material on 

 them in order that it will enter their respiratory system. 

 Since they are killed only by such contact sprays it is neces- 

 sary to spray every portion of the plant bearing insects. It is 

 frequently wise to spray two or three times a week if the 

 infection is serious. Tobacco decoction (Black Leaf Forty), 

 or kerosene with a soap emulsion is useful for aphids and 

 plant lice. In addition to being an excellent contact spray, 

 rotenone is very effective as a repellent to many insects. 

 Early experimental reports indicate that when released from 

 war duty a new chemical dichloro-diphenyl-trichloro-ethane 

 called DDT will be the best all around insecticide. It not 

 only acts both as a stomach and a contact poison but retains 

 its effectiveness over a long period. Warning! It kills bees. 

 Lime sulphur is usually used as a dormant spray for scale 

 insects. 



Diseases caused by bacteria or fungi are controlled in two 

 ways. First, destroy all diseased plant material whenever 

 it is found and especially in the late fall, to avoid keeping 

 the disease from one season to another. Second, spray regu- 

 larly with a fungicide in order to keep the new leaves covered 

 with a spray material. Spraying once each week is usually 

 enough. This protects the plants against the spread of dis- 



