32 BULLETIN 1118, U. S. DEPARTMENT OF AGRICULTURE. 



by injurious or even disastrous effects from later insect attack. 

 Bordeaux mixture is the most effective spray against scab, and 

 when made up with lake or shallow well (soft) water spray injury 

 seldom follows. Usually deep well (hard) water is satisfactory, 

 but a few instances are on record where a moderate amount of spray 

 burn has resulted from Bordeaux mixture being made up with such 

 water and applied on citrus trees. In certain localities hard water 

 can be used with safety, while in others it is likely to be followed 

 by more or less spray burn. Unless extra applications of insecticides 

 are made, scale insects are very likely to increase rapidly and do 

 great damage following this spray. Commercial Bordeaux prepara- 

 tions (Wallace, 31) when used in sufficient quantities to give about 

 three-sixteenths of 1 per cent copper in the diluted spray are effective 

 though expensive substitutes for homemade Bordeaux mixture. 

 Bordeaux mixture plus oil emulsion is equally as effective against 

 citrus scab as is plain Bordeaux mixture and against insects as 

 is the same strength of oil emulsion when applied separately. 

 The fungicidal effects outlast the insecticidal effect, and for this 

 reason the -usual treatment and sometimes extra applications for 

 scale are required following the use of Bordeaux mixture plus oit 

 emulsion. Burgundy mixture is quite effective against citrus scab, 

 but if not carefully made is likely to cause some injury to fruit or 

 foliage. This spray is considered too risky for general use. Scale 

 insects become very numerous following applications of this material. 

 Ammonical copper carbonate solution is much less effective against 

 citrus scab than is Bordeaux mixture. In general, it is not a desir- 

 able spray for scab control. Scale insects increase considerably fol- 

 lowing its use. Lime-sulphur solution, 32° B., diluted 1 to 40, is 

 not more than 50 per cent effective against severe scab infection, 

 but for certain reasons it can be applied profitably in many orchards. 

 No spray injury has been observed where this material was used 

 during the spring for scab control. This spray kills red spiders, 

 rust mites, and scale crawlers. Dry lime-sulphur and barium sul- 

 phur when used on the basis of sulphur equivalents of standard 

 lime-sulphur solution, seem to be fairly satisfactory but quite ex- 

 pensive substitutes for the commercial lime-sulphur solution. Soda- 

 sulphur or sodium-sulphur compounds are expensive and compara- 

 tively ineffective substitutes for lime-sulphur solution for use against 

 scab. The hazard of spray burn is especially great following the 

 use of sodium-sulphm- compounds of fungicidal strengths. 



Dusting for the control of citrus scab has not been tested thor- 

 oughly. There seems to be no good reason for assimiing that dusting 

 with materials now used will prove as effective or as practical as 

 spraying. 



