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Lime- Sttlphub as a Fux-gicide. 



[Feb., 



A- closely allied wash, ammonium poly sulphide, discovered in 

 1916 (6) (7; (8), which leaves no visible deposit on the sprayed 

 parts, can be recommended for the purpose, but this wash is in 

 disfavour with the manufacturing horticultural chemist, owing 

 to the difficulties met with in its preparation. 



With regard to the use of lirne -sulphur as a summer-wash on 

 apples for the control of " scab," the expectation (raised by 

 reports from the United States; that it would control this disease 

 as well as Bordeaux mixture does., and without causing any injury 

 to the tree, has not been fulfilled. Not only may serious 

 defoliation result on certain varieties (e.g., Stirling Castle, 

 Newton Wonder) after spraying with liine-sulphur, but, accord- 

 ing to the experiments (9) (10) lately carried out at the East 

 Mailing Research Station, a reduction of crop (due to the young 

 apples falling off) may be caused. 



In view of the above facts, it is obviously a matter of great 

 practical importance to ascertain as closely as possible the exact 

 strength of lime -sulphur which is necessary to kill the fungus, 

 in order to see whether any of the ill-results which now follow 

 the use of lime -sulphur under certain circumstances can be 

 avoided by using it in a weaker solution. . Although much work 

 has been done in the orchard and plantation in spraying trees 

 with lime-sulphur solutions of various strengths, it does not 

 appear that carefully controlled biological observations on the 

 sprayed fungus — such as can be made on plants grown under 

 glass — have hitherto been recorded. The present article 

 describes the results of experiments which have determined the 

 strength of lime-sulphur necessary to kill the " summer," or 

 cdn&ial, stage of one of the " powdery " mildews, viz.. the 

 Hop-mildew (Sphaerotheca Humuli (D.C.), Burr.). 



Description of Experiments. — The plants used in the spray- 

 ing experiments were young hop-plants, grown in a greenhouse, 

 infected with the hop-mildew. In previous work (11) it had been 

 found that the mildew in dirrerent stages of development shows 

 very different powers of resistance to the same fungicide. By 

 the selection of only those patches of mildew in the same stage 

 of development, i.e., the so-called " powdery " patches of the 

 eonidial stage,* and on young vigorously growing leaves, it is 

 r jssible to keep a sufficiently fixed standard by which to measure 

 satisfactorily the fungicidal value of different solutions. 



If a lime-sulphur solution — even in the finest possible 



misty " spray, such as that given by an " atomiser " — is 



- ;: An illustration of this stage is given in the article by E. S. Salmon, 

 " Hop-mould and its Control " (Jour. Min. A grid., May 1921, p. 150, Fig. 2). 



