9 



Compatibility of the Ingredients in the Combination Spray as Affected 

 BY Addition of Lime, Calcium Caseinate, and Order of Mixing. 



Apples are not often sprayed with lime-sulfur alone. They are now more often 

 sprayed with a mixture of Hme-sulfur, lead arsenate, nicotine sulfate, and calcium 

 caseinate. The reaction between lead arsenate and lime-sulfur has been studied 

 by Ruth (17) and others, and it is known that both of these materials are some- 

 what decomposed, one of the results being the formation of the black sludge, 

 lead sulfide. Relative blackness of the mixture is an indicator of its lack of de- 

 sirable qualities. So far as is known, the addition of nicotine sulfate does not 

 affect this reaction. It has been shown by numerous investigators that the addi- 

 tion of arsenate of lead to hme-sulfur increased the fungicidal value of the latter. 

 Although the use of such a combination spray controls apple scab as weU or 

 probably better than lime-sulfur alone, the formation of soluble arsenic as a result 

 of the reaction increases the danger of foliage burning. 



It has been found by Robinson (18) that by the addition of lime to tliis com- 

 bination spray, the percentage of the soluble, and therefore dangerous, arsenic in 

 the combination spray can be reduced. After standing two days, most of the lime- 

 sulfur ■wdth lime added remained unchanged, while in Ume-sulfur alone, the de- 

 sirable polysulfide sulfur had all been changed into lead sulfide or thiosulfate. 

 Bourne (19) modified Robinson's method by adding milk-of-hme to lead arsenate 

 and then adding the two together to diluted lime-sulfur. He found this resulted in 

 very httle sediment or blackening. He diluted hme-sulfur till the spray tank was 

 nearly full. Lime (at the rate of 10 pounds to 100 gallons of the total mixture) 

 was slaked and water added to make a milk. Arsenate of lead was stirred into the 

 milk-of-lime, which was then strained into the spray tank with the agitator running. 

 Krout (2) compared liquid Ume-sulfur with liquid Ume-sulfur plus Ume in the 

 field. In each of the three orchards where he used it, there was no russeting of the 

 fruit by either Ume-sulfur alone, or Ume-sulfur with lime added, and so the benefit 

 of the addition of lime in reducing burning was not shown. In each of the three 

 orchards sprayed by Krout, the addition of Ume to Ume-suhur was foUowed by 

 an increase in the percentage of scabbj^ fruit over the percentage on trees sprayed 

 with Ume-sulfur A\'ithout lime, the increases being 10, 3, and 8 per cent, respectively. 



In the experiments of 1923, there was no russeting or burning on trees sprayed 

 with lime-sulfur or on those spraj^ed with. Ume-sulfur plus Ume. Hence in 1923, 

 as in 1922, it was impossible to prove that the addition of Ume to Ume-sulfur re- 

 duced the toxicity of the fungicide to the spraj'ed tree. In both of the orchards 

 where these materials were compared in 1923, a larger percentage of scabby apples 

 was produced on trees sprayed with Ume-sulfur plus lime than on trees spraj^ed 

 with Ume-sulfur mthout Ume added, the increase being 1.2 per cent in one case 

 and 5.3 per cent in the other. The indications are that the addition of Ume to the 

 lime-sulfur-lead arsenate combination spray reduces somewhat the fungicidal 

 efficiency' of the latter. In seasons when cUmatic conditions result in toxicity 

 to the sprayed tree by the Ume-sulfur-lead arsenate combination spray, it is possi- 

 ble that any smaU decrease in fungicidal efficiency coincident with the addition 

 of lime would be more than offset by the decreased danger of burning described by 

 Robinson (loc. cit.) and Bourne (loc. cit.). However, further experimental evidence 

 is needed. 



According to Regan (20) the addition of calcium caseinate spreader to Ume- 

 sulfur-lead arsenate combination spray prevents the usual decomposition and 

 formation of black sludge. He found two pounds of calcium caseinate to be more 

 effective in preventing tliis decomposition than ten pounds of hydrated Ume. 

 Lovett (21) also reports that the addition of calcium caseinate materiaU}^ delays 

 the reaction between lime-sulfur and lead arsenate in the combination spray. 



Laboratory tests were made by the writer to compare the formation of black 

 sludge in "the combination spray with and without the addition of calcium caseinate. 

 Without calcium caseinate, the color of the mixture was dark citrine^ and with 

 it the color was yellowdsh citrine, that is, considerably Ughter. After standing 

 three minutes the sludge precipitated wdthout calcium caseinate was nearly twice 



1 Colors determined by comparison with Ridgway, Robert. Color Standards and Nomenclature. Wash- 

 ington, 1912. 



