No. 6. DEPARTMENT OF AGRICULTURE. 765 



sion by fungi, and even in the advanced stages the fungi present are 

 chiefly such as live upon dead plant tissue only. 



"Tip-burn is not caused by the attacks of parasitic fungi. It is 

 rather attributable to the unfavorable conditions surrounding the 

 plant, especially to the dry hot weather with insufficient water sup- 

 ply. It is aggravated by any other conditions which tend to lower 

 the general vigor of the plant, such as insufficient food supply, and 

 attacks of insects and the early blight fungus. This difficulty has 

 not been observed to any serious degree upon plants until after they 

 pass the blossoming period, and naturally begin to weaken. 



"As the older leaves weaken, especially the lower leaves of the 

 plants, the tissues of the interior of the leaf sometimes develop dead 

 spots surrounding flea beetle punctures or other injuries. These 

 spots soon dry and show distinct rings and bear a general resem- 

 blance to the 'ringed spots' caused by Paris green and by the early 

 blight fungus. They may occur, however, in the absence of both 

 these causes. Dr. Sturgis, describing these spots in his Keport for 

 1894, attributed them to the effects of dry, hot weather. We believe 

 this to be the correct explanation and would therefore associate them 

 with 'tip-burn' rather than with the true 'early blight.' 



"Prevention. — Effort should be made to increase and sustain the 

 general vigor of the plant by proper selection of varieties, prepara- 

 tion and cultivation of the soil, and protection against the attacks of 

 insects and fungi. The only thing that can be done in addition is to 

 irrigate in times of extreme drouth," . 



Potato Scab. — The unsightly appearance of many tubers is due to 

 scab. This is a fungous disease with which most growers have op- 

 portunity of acquaintance. An immense amount of work has been 

 done by our Stations in study of the disease and in attempts to pre- 

 vent its ravages. Some years ago the scab was attributed by grow- 

 ers and investigators to a variety of agencies, such as stable manure, 

 insects, lime, etc., but the Connecticut and North Dakota Stations 

 demonstrated bevond chance of doubt that the iniurv to the tubers is 

 pi-oduced by a fungus i^Oos^pora scaMex). The following statement, 

 taken from Bulletin 19 of the North Dakota Station, states the facts 

 concisely: 



"Potato scab is due to the growth of a fungus upon the young po- 

 tato tubers while they are developing in the ground. The disease 

 is communicated to the new crop by way of the seed tubers, or by 

 way of the soil or old potato tops, if the potatoes are planted upon 

 old ground, the germs having remained over from previous crop. If 

 an old potato patch is in the near neighborhood the disease may 

 also be communicated by wash water, or, perhaps, through dust 

 blown from the old patch. If, however, there are no disease hearing 



