338 JOUR.NAI. OF THE DKrAKTMENT OF AgKICULTURE. 0(T., 1922. 



Experiments liave beeu uudeitaken and will be continued to« 

 determine (a) whether a cheaper spray than niiscible oil may be used 

 for the control of led scale, (b) if one dormant spray application of a 

 concentrated lime-sulphur mixture will control red scale, (c) if foliage 

 applications of concentrated lime-suli)hur, diluted to approximately 

 1 degree Beaume. which are much cheaper than Bordeaux, may be 

 used to advantage as a combination spray for the control of red scale^ 

 mites, and fusicladium. The general purpose of these experiments i& 

 to ascertain if it may be possible for the fruit grower to lessen con- 

 siderably the expense of producing a crop of first class pears. 



Spraying with concentrated lime-sulphur in late winter, at a 

 strength of 4-5 degrees Beaume, for the control of red scale on pear 

 trees has been, and is, practised with varying results by many fruit 

 growers in South Africa. A study of the question of how lime- 

 sulphur kills scale insects (1) indicates that this material has the 

 ability to soften the wax about the margin of the scale insect, clamp- 

 ing it against the surface of the plant, and smothering the insect 

 under the scale. In addition to this property, the lime-sulphur 

 deoxidizes or removes and absorbs some of the oxygen from about the 

 body of the insect under the scale. Young scale insects that are 

 produced by adult female scale insects which survive the dormant 

 spray, craAvl away from beneath the bodies of the latter, and are killed 

 by the fumes of sulphur dioxide, which slowly arise from the lime- 

 sulphur dormant spray for some time after it has been applied to the 

 plant. The length of time this gas will arise and be of sufficient 

 concentration to kill the young scale insects is undoubtedly influenced 

 by the temperature and rainfall for several weeks following the appli- 

 cation of the spra}-. The variation each season in these two factors, 

 and the difference in the time of application of the winter spray 

 very probably results in a variation in the efficiency of the spray 

 material. 



Records of spray experiments carried out by the writer during 

 the 1920-1921 fruit season at Elsenburg, (2) show that Kiefier pear 

 trees spraj^ed with commercial concentrated lime-sulphur, diluted at 

 the rate of 1 measure in 10 measures of water, of 4 degrees Beaume,. 

 applied in late winter, before buds had opened, produced 45 per cent, 

 of fruit infested with red scale in comparison with 5 per cent, infesta- 

 tion for trees sprayed with 1-10 dilution in late winter, one foliage 

 spray just before blossoming, and later with two foliage sprays of 

 concentrated lime-sulphur, diluted 1-40, applied with lead arsenate 

 at the time of the two first codling applications. Beurre Hardy and 

 Duchesse pears sprayed with lime-sulphur diluted 1-20 in late winter, 

 before buds had opened, produced respectivelj" 3.3 per cent, and 

 44 per cent, scale-infested fruit in comparison with nine-tenths of 

 1 per cent, and 9 per cent, respectively for trees sprayed at the same 

 time with 1-20 diluted lime-sulphur and later with two foliage spiays,. 

 diluted 1-40, sprayed during the first two applications of lead arsenate 

 for control of codling-moth. 



Table I, recording results of experiments in red-.scale control for 

 the 1921-22 fruit season confirms the results obtained the previous 

 season. Records show that one application of concentrated lime-sul- 

 phur, applied as a dormant spray, w^hether diluted at the rate of 

 1 measure of lime-sulphur in 6^ measures of water, in 8 measures of 

 water, or in 10 measures of water, will not satisfactorily control this 



