196 FUNDAMENTALS OF FRUIT PRODUCTION 



Arsenic. — Arsenic is another mineral toxic to plants in exceedingly 

 small amounts. In many of the higher plants exposure to a concentra- 

 tion of 1 part in 1,000,000 is sufficient to inhibit growth. ^^^ When arsenic 

 is absorbed by the roots, they show its effects first. 



The toxic effects of arsenic on fruit trees are described in an article in the 

 Horticulturist. ^°2 "When a little arsenic is introduced into the circulation of 

 a fruit tree at that season (early spring) it first discolors the sap vessels of the 

 inner bark, then the leaves suddenly flag, and droop; the branch shrivels and 

 turns black; and finally if the dose is large enough, the whole tree dies." Stimu- 

 lating effects from arsenic have been observed, presumably when absorption was 

 restricted to amounts smaller than that indicated above as toxic. 



The question of the toxic action of arsenic is one of much interest 

 since nearly all deciduous orchard fruits require one or more applications 

 of arsenical sprays each year. In old bearing orchards the total arsenic 

 used per acre each year is Hkely to be as much as 4 pounds, figured as 

 arsenic trioxide. Though applied directly to the foliage and fruit, most 

 of it reaches the ground in the course of the season. It is generally 

 applied in some very insoluble and chemically inactive form, such as 

 arsenate of lead. However, there is a considerable accumulation, espe- 

 cially in the surface soil, as spraying is continued. This has led to con- 

 siderable uneasiness among growers and much injury has been reported 

 to be due to these accumulations in some of the irrigated sections. The 

 injury has taken the form of collar and root rot and in addition it has 

 often been followed by premature ripening of the fruit and wood in the 

 fall and the death of the tree the following year. However, it is only in 

 irrigated sections and in soils with a rather high alkali content that this 

 trouble has been encountered. This suggests that the injury is attribu- 

 table to the action of various alkali salts reacting with the arsenic to make 

 it soluble, to the combined action of alkali salts and arsenic, or possibly 

 to alkali salts alone, since similar injuries are known to result from alkali 

 poisoning. Results with Ben Davis apple trees sprayed in one season with 

 as much arsenic as ordinarily would be apphed in 10 to 40 years and under 

 conditions where soil alkali was not a factor, have led to the conclusion 

 that such arsenical poisoning as has been reported from certain sections 

 is not attributable to the arsenic.^ Some of these applications were so 

 heavy that the trees not only remained whitened all summer, but the 

 "ground under the entire head of the tree was so saturated with the 

 arsenic as to appear moldy white to a depth of 3 or 4 inches." No injury 

 appeared in the trees or even in the vegetation (including strawberries, 

 alfalfa and a number of weeds) under some of them. This makes it 

 evident that little is to be feared from the toxic effect of the arsenic used 

 in spraying unless the soil has a fairly high alkali content and then the 

 problem is one of dealing with the alkali rather than with the arsenic. 

 Arsenic is, however, a contributing factor. Ewert^^ believes that there is 



