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 wdth lime-sulfur alone. They are now more often 

 sprayed with a mixture of lime-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 lime-sulfur increased the fungicidal value of the latter. 

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

 probabl}' 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 this 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 hme- 

 suLfur with lime added remained unchanged, while in hme-sulfur alone, the de- 

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

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

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

 very Uttle sediment or blackening. He diluted lime-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 lime-sulfur with liquid lime-sulfur plus lime in the 

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

 fruit by either lime-sulfur alone, or lime-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 Hme to lime-suKur was followed by 

 an increase in the percentage of scabby fruit over the percentage on trees sprayed 

 with lime-sulfur without lime, the increases being 10, 3, and 8 per cent, respectively. 



In the experiments of 192.3, there was no russeting or burning on trees sprayed 

 with lime-sulfur or on those sprayed with hrae-sulfur plus Ume. Hence in 1923, 

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

 duced the toxicit}^ 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 lime-sulfur plus lime than on trees sprayed 

 with hme-sulfur without hme 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 hme to the 

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

 efficienc.y of the latter. In seasons w^hen climatic conditions result in toxicity 

 to the spraj^ed tree by the lime-sulfur-lead arsenate combination spray, it is possi- 

 ble that any small 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 lime- 

 suhur-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 this decomposition than ten pounds of hydrated lime. 

 Lovett (21) also reports that the addition of calcium caseinate materially delaj^s 

 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 yellowish citrine, that is, considerably lighter. After standing 

 three minutes the sludge precipitated without calcium caseinate was nearly twice 



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

 ington, 1912. 



