72 TRACE ELEMENT DEFICIENCY 



margined holes are scattered over the leaf. Internode develop- 

 ment is poor and finally the branches die back. The development 

 of lateral buds below the dead region results in the rosette 

 appearance from which the disease takes its name. A morpho- 

 logical examination by Finch and Kinnison of the roots of 

 affected trees revealed no indication of an abnormal condition, 

 either externally or internally. 



Death of the tree rarely, if ever, results from rosette, but fruit 

 production may be so poor that the cultivation of the trees 

 becomes unprofitable, and in 1932 Alben, Cole and Lewis stated 

 that in some south-eastern states hundreds of acres of pecan 

 orchards had been abandoned on account of rosette, while in 

 south-western states where plantations were more recent, as 

 many as 95 per cent of the trees were rosetoing in some places. 

 There can thus be no doubt of the economic importance of 

 pecan rosette. 



Researches by Orton and Rand (1914) showed fairly con- 

 clusively that the disease is not due to the attack of any micro- 

 organism, nor did it appear to be limited to any type of soil. 



At first it appeared that the disease might be related to iron 

 deficiency, for Alben, Cole and Lewis (1932a) found that some 

 improvement in rosetted leaves was brought about by dipping 

 them in, or spraying them with, a 0-6-1 per cent solution of 

 ferric chloride or ferric sulphate. 



A little later, however (19326), they found that favourable 

 results by such treatment were obtained only when galvanized 

 iron containers were used for the solutions. This suggested the 

 possibility that the effect at first attributed to iron might be 

 due to zinc salts present as impurities in the iron salts used, 

 and accordingly treatment with solutions of zinc chloride and 

 zinc sulphate was tried. It was found that an immersion of the 

 terminal branches of trees exhibiting rosette in a solution of an 

 iron salt produced no improvement in the condition of the 

 leaves, but that with a solution of a zinc salt young leaves were 

 restored to their normal condition. Similar favourable results 

 were obtained by the use of zinc-lime and zinc-sulphate sprays. 

 Alben, Cole and Lewis concluded from their experiments that 

 zinc is essential for the healthy growth of the pecan tree. 



Similar conclusions with regard to the cause of pecan rosette 



