20 MASS. EXPERIMENT STATION BULLETIN 201. 



applied at strengths required for efficient insect control "without injury to 

 foliage, and, moreover, it can be combined wnth other standard sprays 

 (lime-sulfur, lead arsenate, etc.) without impairing either their efficiency 

 or its own. 



The amount of dilution recommended varies according to the resistance 

 of the insects for the control of which it is applied, ^\^len used at a dilu- 

 tion of |-J pint in 50 gallons of water (or, where only a few plants are 

 to be treated, 1-lf teaspoonfuls to 1 gallon of water), nicotine sulfate 

 is efficient for the control of the average soft-bodied sucking insects of 

 orchard and garden. When nicotine sprays are used alone in water, the 

 addition of soap, 2-4 pounds to every 50 gallons of spray (f-1 ounce to 

 1 gallon), increases their spreading power and general effectiveness. With- 

 out soap the nicotine solutions show a tendency to form into drops which 

 roll off the leaves without penetrating to and thoroughly wetting the 

 insects. When nicotine sprays are used in combination with other in- 

 secticides the soap should never be added, owing to the breakdowTi of these 

 chemicals in the presence of the strong alkali of the soap, with the con- 

 sequent formation of compounds dangerous to foliage. (See page 12.) 

 Recent studies upon the effects of nicotine as an insecticide (30) have 

 shown that, regardless of the form in which it is employed, the kilUng 

 action is by paralj^sis, through the penetration of the nicotine vapors into 

 the body of the insect. The effectiveness of nicotine spraj^s, therefore, 

 depends on the amount of nicotine released. The experiments of Graham 

 and Moore (31) have indicated that nicotine sulfate alone is nonvolatile, but 

 if a solution of this material is treated with soap to render it alkaline, 

 nicotine is at once released. Inasmuch, therefore, as the vapor of nicotine 

 is the principal cause of the death of insects spraj^ed with tobacco solu- 

 tions, the maximum efficiency of solutions containing nicotine sulfate 

 can only be obtained by insuring that the spray is rendered alkaline. This 

 is best attained by the addition of soap. 



Within the last few years nicotine sulfate has been used, with lime and 

 kaolin as carriers, in a dust application for the control of the w-alnut aphis 

 and various truck crop insect pests, in Cahfornia. In this form it has 

 demonstrated a killing efficiency and rapidity of action superior to the 

 spray applications. Furthermore, it can be applied faster and costs less 

 than wiien applied in liquid form. So far as known, this has not as yet 

 been used in Massachusetts. Its convenience of application and rather 

 remarkable success as far as tried make it a promising form of application, 

 especially in market gardens. 



5. Pyrethrum. 



Pyrethrum, Persian or Dalmatian insect powder, is the pow'dered flowers 

 of Chrysanthemimi cmerarioefolium: and Buhach, the California product, 

 the powdered flow^ers of C. coccineum. The bright yellow powder owes its 

 insecticidal value to the presence of certain volatile oils, contained in the 

 flower heads, wiiich are quite poisonous to insects, but apparently harmless 



