30 BULLETIN 1118, U. S. DEPARTMEITT OF AGRICULTURE. 



The following year citrus scab did not become at all serious until 

 the rainy season set in, and for that reason the stunting effect was 

 not particularly marked. 



No spray injury was noted until hot weather set in, then consid- 

 erable scorching of mature leaves and blighting of tender shoots 

 was usually experienced on plats sprayed with lime-sulphur solution. 

 Defoliation was very serious with the sour orange, but not quite so 

 marked in the case of the rough lemon. Oil emulsion added to the 

 lime-sulphur solution increased the injury by about 20 per cent. 

 Neither material (formulas 9 and 10) gave more than 50 per cent 

 control. 



Burgundy mixture (formula 7) produced a slight russeting of 

 foliage, but not in sufficient proportions to be considered serious. 

 Nevertheless, with a slight excess of either the sal soda or the blue- 

 stone, considerable damage is likely to occur, and for that reason 

 it appears to be too treacherous to be employed in ordinary nursery 

 work where unskilled labor has to be relied upon to attend to the 

 preparation and application of the sprays. This material gave 

 perfect coi>trol of scab. 



Copper soap (formula 8) gave very pleasing results. No injury 

 was found on the trees sprayed with this material. This formula 

 carries an excess of soap and apparently is quite safe for use. It 

 controlled scab perfectly. 



Plain Bordeaux mixture (formula 1) controlled scab perfectly, 

 and no spray injury resulted. The chief objection to copper sprays, 

 especially Bordeaux or Burgundy mixtures, is that scale insects 

 usually become very numerous following such applications unless 

 drastic measures are taken to prevent these insects from multiplying. 



Bordeaux mixture plus oil emulsion (formulas 2, 3, 4, 5, and 6) 

 evolved especially to overcome the objectionable aftereffects of 

 plain Bordeaux mixture, also controlled scab perfectly. It adheres 

 as well as plain Bordeaux mixture and spreads much better. The 

 weaker formulas of Bordeaux mixture gave equally as good results 

 as the stronger materials. Where this combination spray was 

 applied, scale insects were held down satisfactorily without extra 

 sprayings. No injury resulted from the use of any of these formulas. 



COMMERCIAL CONTROL. 



While the actual control of citrus scab per se by means ol sprays 

 is not especially difficult if the spraj^ing is done with thoroughness, 

 at the proper time, and mth effective materials, the commercial 

 control of scab on grapefruit presents numerous factors for considera- 

 tion, some of which are extremely important. 



Perhaps the most important single factor, in so far as the well- 

 being of the tree is concerned, is the beneficial or entomogenous 



