b CIRCULAR 862, U. S. DEPARTMENT OF AGRICULTURE 



vegetable crops failed or were injured when planted on orchard 

 sites from which the trees had been recently removed after many 

 years of spraying with lead arsenate. Peach and apricot trees 

 planted on old apple orchard land sometimes showed typical ar- 

 senic injury. Arsenic toxicity in such soils slowly decreased over 

 a period of many years after arsenic applications were discon- 

 tinued. 



Paden and Albert (33), Cooper and others (11, 12), Albert 

 (2), Reed and Sturgis (36), and Fleming and others (15) all 

 have shown that some annual crops are injured by arsenic resi- 

 dues in the soil following the use of lead arsenate or calcium 

 arsenate for insect control on cotton and other crops other than 

 orchard trees. Although many years' residue accumulation or 

 massive doses of arsenical insecticides to the soil are required 

 to produce crop injury under most conditions of use, that is not 

 always true. On some light soils that are low in iron content as 

 little as 50 to 150 or up to 300 pounds per acre of calcium arse- 

 nate has impaired growth of rice, soybeans and other legumes, 

 and other crops. The grain crops and potatoes are usually fairly 

 tolerant to arsenic, but most vegetable crops are sensitive. In 

 view of all the evidence it is probable that many less striking 

 instances of harm from arsenic residues have escaped attention 

 or have been wrongly ascribed to other causes. 



Synthetic Organic Substances 



Since 1945 many reports have appeared concerning the effects 

 of several of the new T er organic insecticides on plants when those 

 substances became mixed into the soil. The preponderance of 

 reports showing injury is due partly to the fact that numerous 

 investigators purposely included large dosages of the materials 

 being studied in order to find the maximum amounts of each that 

 a given plant would tolerate in the soil without harm. In gen- 

 eral, the reports show clearly that these new insecticides are 

 definitely harmful to plants when present in the soil in large 

 amounts. They also show that some are injurious in amounts 

 that are not very large and which may be encountered under 

 conditions of practical use — or misuse. 



The reports, cited here refer to an extremely wide range of 

 crops, soils, methods, materials, and even purposes for which the 

 respective studies were made. No two studies were conducted 

 exactly alike, and, therefore, none are very closely comparable. 

 It is not feasible here to present enough details about each one 

 to permit the reader to make his own evaluation or interpreta- 

 tion of the results mentioned. Only the general trends of the 

 findings are given, with citations, in an effort to suggest the 

 pattern of plant responses that is beginning to emerge from the 

 heterogeneous mass of gradually accumulating evidence. 



DDT 



Patrick and others (3J^) reported that dry seeds may be dusted 

 or coated with dry DDT without impairing the viability or vigor 



