64 



MELON RUST. 



(Glceosjwriumtinclemutlrianum, Sacc. & Magnus.) 



I send inclosed a number of melon leaves affected with a disease commonly known 

 iu this region as rust. The disease is very destructive, especially if the weather is 

 hot and moist. Any information as to the cause of the disease and the existence 

 of a remedy will be thankfully received.— (Edward Tillett, Harbinger, N. C.) 



Answer. The disease of the melon known as "rust" is caused by a par- 

 asitic fungus which grows in the tissues of the leaves and rind. This 

 fungus is a plant like the vine upon which it lives; unlike the latter, 

 however, it has not the power of obtaining its food from the soil and 

 air, but depends entirely upon the juices of the vine for sustenance. In 

 order to build up its own body the fungus robs the melon plant of its 

 nourishment, and as a result of this action the tissues turn brown or 

 " rust." 



With the aid of a microscope it is an easy matter to see little tufts of 

 the fungus seated upon the brown spots, and further manipulation shows 

 that these are made up of an immense number of spores or reproduc- 

 tive bodies. The reproductive bodies being very minute are easily 

 wafted from place to place by the wind, and when they fall upon healthy 

 vines, and the proper conditions of moisture and heat are present, they 

 germinate just as seed will germinate when placed in a warm, moist soil. 

 In germinating, the spores send out slender tubes which penetrate the 

 tissues and ultimately give rise to the u rust" spots again. 



Heavy dews, fogs, or an excess of moisture in any form favors the 

 development of the fungus, and this fact explains why the rust usually 

 appears during the prevalence of wet weather. It is possible that the 

 disease may be prevented by the application of some substance to the 

 plants which will prevent the spores of the fungus from germinating, 

 but so far as we are aware no experiments having a bearing on this 

 question have been undertaken. By way of trial I would suggest that 

 you spray the vines with a solution made as follows, taking care to 

 thoroughly wet the leaves, but not to drench them: 



Dissolve 1 pound of sulphate of copper in a gallon of hot water; to 

 this solution add 1 pint of liquid ammonia, a little at a time, until all 

 the copper is precipitated ; the liquid is then turbid and blue in color. 

 Add 2 or 3 gallons of water and let stand to settle. Pour off the clear 

 liquid, which contains sulphate of ammonia — the compound which causes 

 the burning of the leaves. Then pour upon the precipitate left in the 

 vessel just enough liquid ammonia to dissolve it. The result is a clear 

 liquid of a beautiful deep blue color. When required for use, dilute to 

 22 gallons. 



It would be well to make one application of this solution about the 

 middle of July, as the disease rarely appears earlier thau this date. It 

 must be borne in mind that the copper acts merely as a preventive^ 

 therefore it should be applied before the disease makes its appearance. 



