8 FARMERS’ BULLETIN 674. 
practically as effective in controlling the citrus thrips as lime-sulphur, 
can, not be purchased ready-made and is therefore less convenient to 
handle. Furthermore, at the present writing it costs Just as much 
per dilute gallon as the factory-made lime-sulphur. 
The sulphur-soda stock solution is prepared as follows: 
Powdered ‘sulphiur-emee-. ------- -- ager ae - te 30 pounds. 
Powdered caustic soda(98 per cent) epee... 2 bl. 15 pounds. 
Waterttolimalke sae eeere 2... es eee 30 gallons. 
The sulphur is made into a paste with water, and while the mix- 
ture is being constantly stirred the soda is added in sufficient quantity 
to start boiling. As boiling becomes violent a litile water is added 
co retard it. When the sulphur has all been taken mto solution 
enough water should be added to bring the stock solution up to 30 gal- 
lons. If made according to the foregoing directions the final product 
will be a clear, amber-colored liquid much resembling good commer- 
cial lime-sulphur. 
PLAIN TOBACCO EXTRACTS. 
Tests with plain tobacco extracts without the addition of lime- 
sulphur or other preparations have given very good results when the 
tobacco has been used at sufficient strength. Tobacco extract con- 
taining 40 per cent nicotine used at the rate of 1 part-to 800 parts, 
liquid measure, of water is quite satisfactory ; when diluted at the rate 
of 1 part to 1,600 parts water, however, its efficiency is noticeably 
lowered. It can not be recommended for this work in solution weaker 
than 1 to 1,000, and should preferably be used at the rate of 1 to 800. 
The commercial tobacco extract contaming a high percentage of nico- 
tine sulphate is very convenient to handle and costs approximately 
$0.016 for each gallon of the diluted spray, when used at the rate of 
1 part to 800 parts of water. 
TIME AND NUMBER OF SPRAY APPLICATIONS. 
Unfortunately no specific dates, which will hold for every season, 
can be fixed for the applications of the spray. The investigations of 
the seasons of 1910 and 1911 have shown that the date on which the 
thrips first become numerous and injurious and the navel-orange 
blossoms lose their petals varies as much as 30 days in certai seasons, 
due to the nature of the spring weather, and, further, that it varies in 
different orchards in the same season. The greatest injury to the 
fruit is done between the time the petals fall and the fruit is half 
grown. It has been demonstrated that three applications of the 
insecticide are necessary during this period to prevent marking of 
the fruit. The first spring growth has usually hardened by the time 
