24 BULLETIN 256, U. S. DEPARTMENT OP AGRICULTURE. 



As shown in Table III, two applications of arsenite of zinc, at the 

 rate of 2 pounds per 100 gallons plain water (plat 7) or dilute lime- 

 sulphur solution (plat 1), gave practically the same results as one 

 application at the rate of 4 pounds per 100 gallons (plat 3), being 

 sufficient in each case to kill the katydids and insure approximately 

 100 per cent sound fruit. Two applications of arsenate of lead, at 

 the rate of 4 pounds per 100 gallons plain water (plat 9) or dilute 

 lime-sulphur solution (plat 4), were practically as effective as the 

 arsenite of zinc and gave just as good results as when used at the 

 rate of 8 pounds per 100 gallons with but one application (plat 6). 



The addition of lime-sulphur to the arsenicals, besides being abso- 

 lutely essential where it is desired to control both katydids and the 

 citrus thrips, increased the adhesive quality of the arsenicals and 

 facilitated their even distribution over the leaves and fruit. This 

 was especially noted after a slight rain, occurring May 25, when the 

 combination sprays appeared to be very little affected. Lime- 

 sulphur solution itself without the addition of arsenicals proved 

 deterrent to the katydids and measurably reduced the amount of 

 injury to the fruit. It also, therefore, appears to have some insec- 

 ticidal value against these insects. 



RECOMMENDATIONS. 



On the basis of the foregoing results the writers make the following 

 recommendations for the control of katydids on oranges in the San 

 Joaquin Valley: 



1. Two applications of arsenite of zinc at the rate of 2 pounds per 

 100 gallons of water; or, 



2. Two applications of arsenate of lead at the rate of 4 pounds per 

 100 gallons of water. 



The first application should be made, at the latest, immediately 

 after most of the petals have fallen; the second application, from 10 

 days to 2 weeks after the first. If it seems desirable to spray for 

 the citrus thrips also, lime-sulphur should be added to the above at 

 the rate of 2 gallons per hundred, and a third application of lime- 

 sulphur only, at the same dilution, should be made about two or 

 three weeks after the second. 



The cost of spraying will vary somewhat according to size of 

 trees, cost of labor, team hire, insecticides, etc., but with ordinarily 

 good management will not exceed $5 per acre. 



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1915- 



