IQII 



BETTER FRUIT 



Page 2g 



DURING SPRAYING TIME IN THE ORCHARD OF W. F. HURST, BOISE, IDAHO 



then sent to the Bureau of Chemistry, 

 United States Department of Agricul- 

 ture, and careful quantitative tests for 

 arsenic were made. The apples, upon 

 receipt, were carefully washed and wiped 

 ofif so as to remove all arsenic that might 

 have adhered to the skin of the apples, 

 and thus leave only the arsenic that 

 had penetrated the tissues. Ten-gram 

 samples of the skins of both Newtown 

 and Spitzenbergs varieties and ten-gram 

 samples of the apparently sound skin of 

 the same varieties were examined for 

 arsenic. The samples taken necessarily 

 included not only the epidermal and sub- 

 epidermal tissues, but a considerable 

 amount of the flesh, which did not neces- 

 sarily contain any arsenic. This was 

 done in order to be sure that all the 

 arsenic was taken. The result of the 

 analysis showed that the black and red 

 spots contained from 0.03 to 0.05 milli- 

 grams, while the apparently sound skins 

 showed 0.025 milligrams of arsenic. No 

 doubt the concentration of arsenic about 

 the injured spots is much greater than 

 analysis show, but, even with the large 

 part of unspotted skin included in the 

 analysis, the badly spotted fruits show 

 approximately twice as much arsenic as 

 the apparently sound fruit. 



One analysis of very badly spot- 

 ted Spitzenberg showed a quantity - of 

 arsenic, which, caluculated as arsenic 

 oxid (As2 O5), equaled about 0.3 milli- 

 grams, or aproximately 0.005 grains. As 

 will be seen, the amount of arsenic is 

 rather small, and there would be no 

 danger of serious poisoning even if such 

 apples were eaten. However, without 

 careful wiping, there is no doubt there 

 might be some slight stomachic disturb- 

 ances if three or four such apples were 

 eaten at one time. The chances for 

 poisoning are so remote, however, that 

 they are hardly worth considering, since 

 it is known that it requires about 0.005 

 grams to have a marked effect. 



SAN JOSE SCALE AND ITS WORK 

 Peach twig, moderately infested, show- 

 ing male and female scale. Enlarged 

 four times 



Knowing that the apples will absorb 

 arsenic in a soluble form, the efforts of 

 manufacturers of lead arsenate should be 

 toward producing a compound not only 

 with the least amount of soluble arsenic 

 present, but so made that any soluble 

 sulphides, chlorides or carbonates in the 

 water used to apply it will not cause 

 the arsenic to go into solution. Without 

 going into the matter technically, and 

 which would be beyond the comprehen- 

 sion of the average reader, it may be 

 stated that when disodium arsenate and 

 lead nitrate or lead acetate are combined, 

 under varying conditions, three forms of 

 lead arsenate are known to occur as a 

 result of the combination. These are 

 the ortho arsenate (Pb.3 (As O4) 2), pyro 

 arsenate (Pb2 As2 O7) and the meta 

 arsenate ( (Pb H As O4) 2). The f^rst 

 contains the smallest percentage of 

 arsenic oxid (As2 O-,), but is, neverthe- 

 less, the best combination, since it does 

 not readily give up free arsenic in the 

 presence of neutral and alkaline solvents. 

 Strictly ortho arsenate of lead will be 

 nearly pure if it contains 13^% arsenic 

 oxid (with 50% water). Commercial 

 samples will range somewhere near 12%, 

 or perhaps a little less. Lead arsenate 

 containing above 12^% to 14% arsenic 

 oxid may be regarded as mixtures of 

 ortho and pyro (or meta), containing 

 from 10% to 50% of the latter com- 

 compounds. Above 14% arsenic oxid 

 the ortho content becomes almost a neg- 

 ligible quantity, at least this is true when 

 the sample shows 15%. Any arsenate of 

 lead which shows more than 16% arsenic 

 oxid may be regarded as unmixed with 

 ortho arsenate. These percentages are 

 to be understood as analysis of leads 

 having 50% water. 



It is a common mistake with most 

 growers to select that brand of arsenate 

 of lead which contains the largest per- 

 centage of arsenate, no matter what the 

 water content may be. Manufacturers 

 are equally at fault in stating that the 

 arsenic content should be high in order 

 that it may be effective in controlling 

 codling moth. Many brands are sold 



purely on the basis of their high arsenic 

 content without any regard to- the form 

 in which the arsenic has entered into 

 combination with the lead. Further- 

 more, it is a well known fact that several 

 brands are acid arsenates, and they 

 could not be otherwise, considering their 

 chemical formula. It must be under- 

 stood by both the grower and the manu- 

 facturer that it is not the excessive per- 

 centages of arsenic that are wanted, but 

 rather a timely and proper application of 

 this important insecticide' correctly com- 

 pounded. Personally I would rather use 

 an ortho arsenate containing 12% of 

 arsenic oxid than one having three or 

 four per cent more. I would be just as 

 sure of results in controlling the moth, 

 and at the same time would feel safe that 

 no injury would result. 



In closing I may say that I would 

 advocate the use of at least one pound 

 of lime (unslaked) with each pound of 

 lead arsenate. This addition of lime will 

 have a tendency to neutralize any arsen- 

 ate which would otherwise have a burn- 

 ing effect. The use of combination 

 sprays is certainly not prohibitive. It 

 has been shown that the combination of 

 lead arsenate with lime-sulphur in the 

 control of both codling moth and scab, 

 as well as the combination of iron sul- 

 phide and lead arsenate in the control of 

 apple mildew and codling moth have 

 generally resulted favorably. This is 

 particularly true in the latter combina- 

 tion, which has been used to a very great 

 extent in the Pajaro Valley, California, 

 and to a lesser extent in the Rogue River 

 A^alley, Oregon. In the Pajaro Valley it 

 has been shown that the addition of iron 

 sulphide to an inferior brand of lead 

 arsenate has really lessened the injury to 

 the fruit and foliage. This is more or 

 less true of any sulphur compound when 

 mixed with the arsenate of lead. 



In the preparation of this article I am 

 particularly indebted to the U. S. Bureau 

 of Chemistry and to Mr. W. H. Volck, 

 horticultural commissioner and entomol- 

 ogist for Santa Cruz County, California, 

 for valuable data and assistance. 



