50 MASS. EXPERIMENT STATION BULLETIN 227. 



ing the spray deep down into the narrow space at the base of the inner 

 leaves. The problem was, therefore, to develop a method of driving the 

 liquid well in among the close-standing plants and force it down into the 

 axils of the leaves; also, to find a spray of superior wetting and flowing- 

 qualities that is toxic to all stages of the insect and has a killing action 

 rapid enough to overcome the active winged adults. 



Nicotine sulfate, the commercial 40 per cent solution, coupled with fisii- 

 oil soap, was found to answer the requirements of a spray. A small Skin- 

 ner System irrigation nozzle, modified to deliver the spray at the desired 

 angle and distribute the pressure evenly, has given good results. This 

 delivers a thin, flat, fan-shaped spray which, with moderate pressure, is 

 broken up into a very fine mist. The full force of the discharge is con- 

 fined to a comparatively small space, so that the spray may be directed 

 upon the portion of the plant desired, with full advantage of the amount 

 of pressure, and with little waste of material. 



This flat spray, directed upon the plants from the side, caused a vibra- 

 tion of the young, limber leaves which, in conjunction with the excellent 

 wetting and flowing qualities of the spray, allowed it to work down into the 

 tight chits and reach the thrips congregated there. From our experiments 

 to date, a steady pressure of 125 to 150 pounds has proven satisfactory, 

 giving a very fine mist and allowing good penetration. 



The most satisfactory spraj' formula used was as follows: 

 Nicotine sulfate ("Black Leaf 40," Nicotine Sulfate 40 per 

 cent", etc.), V^ pint to 100 gallons (1:1500), Good's No. 3 Totash Fish- 

 oil Soap, 6-8 pounds per 100 gallons of spray. 



The soap used in this formula is soft and "pourable", very easilj' 

 handled and mixed into the sipraj'. This product is of such uniform con- 

 sistency that proper dilution can be made by measuring the soap as it is 

 drawn from the container, thus allowing a saving of time when refilling 

 the spray tank in the field. The spray made on the above formula had 

 excellent spreading and "flowing" qualities, and covered the smooth, waxy 

 surface of the onion tops very readily. The most promising feature was 

 its tendency to flow down to the base of the stems and into tlie tight crev- 

 ices, allowing the nicotine to reach and kill the colonies of thrips clustered 

 there. In addition, the alkali of the soap served as an activator of the 

 nicotine, thus hastening its insecticidal action. 



In field tests at North Sunderland, this spray was applied to a section 

 of a large field of onions which had become heavily infested from sets 

 growing alongside. When the sets had been screened and disposed of, 

 this section of tiie field was sprayed, using a power outfit delivering a 

 steady pressure of 12.5-150 pounds, with two lines of hose operating. Owing 

 to the heavy, driving rains and the mildew which had appeared in the field, 

 some of the plants were broken down, making it difficult to make a 

 thorough application. 



Examination of the field the day following the application showed the 

 following: 



Thrips per Average per Control 



100 plants plant Per cent 



Sprayed 165 1- 2 97-f- 



Unsprayed 5230 52-53 — 



Despite the very high percentage of control obtained, a second applica- 

 tion has been found to be advisable, for restocking takes place very rapid- 



