4 MISC. ITBLICATION 13, U. S. DEPT, OF AGRICT'LTimE 



tated. i>iirti(iilarly in iwo diioctions. Tii tlio first phuo because of 

 ilic kiiowlcil^re of the natiiic of (he tlisoasc, (he coiidol work may be 

 phiniu'd \vi(h a iiiiich dealer object in view and \vi(h much U'ss hap- 

 lia/ard expcrimen(a(ion. In the second place the accumuhition of 

 results will be «;i-ea(ly accelerated by means of artificial inoculations 

 both in the «rr('cidiousc and outdoors, because it will not be neces- 

 sai-y to depend on accidental and uncertain natural infection as 

 heretofore. 



Several State and Federal workers in dillerent parts of the coun- 

 try »re en<ra;Lred in investi<;ations on dillerent phases of the |)robleni 

 of controlling? tomato yellows. Some are endeavorin<jj to develop re- 

 sistant varieties, others are trying to discover some spray which will 

 act as a repellent to the insects, and still others are working with 

 differi'Ut measures designed to protect the jilant itself or to enable 

 it to withstand the infection. Consistent results are being obtained 

 by shading the tomato plants with cloth t<'nts or by inteiplanting a 

 tall and fast-growing cioji such as sunllower. In the experiments of 

 the last two years the j)ercentage of yellows was reduced by this 

 means to less than one-half of that in the adjoining control rows. 

 It ai)pears also that it may be advisable, at least in some parts of 

 the country, to remove the shade, which might Ik? objectionable from 

 the viewpoint of production and picking, aft^'r the first part of the 

 sununer. Very little yellows, if any. developed in the bureau's ex- 

 perimental ])lots after the removal of shades about July 1. There 

 are likewise very consistent indications as to the jjresence of resistance 

 in certain varieties, such as some dwarf types, but the degree of 

 natural resistance in these varieties is very slight and is of no commer- 

 cial significance. Work is being carried on to develop new and more 

 resistant varieties. It is hoped that the combined efforts of various 

 investigators will eventually lead to the discovery of such eifective 

 preventive measures as will permit raising tomatoes even in those 

 sections where tomato culture is now i)ractically impossible on 

 account of an extremely high percentage of yellows. 



ADDITIONAL COPIES 



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