DISEASES OF CULTIVATED PLANTS 435 
Fig. 84. Showing a plant of pota- 
to affected with Rosette. The elonga- 
ted injury below the soil surface 
shows as dark-colored in the figure.— 
From Bulletin 139. 
Tip-burn. Potato leaves 
often show dead margins or 
tips even where no parasitic 
attack can be discovered. 
Such ‘‘tip-burn’’ effects may 
also be increased by any extra 
weather stress as of drouth 
or by spray injury. These 
conditions are to be met by 
avoiding the causes which 
bring them about. : 
Wart-Disease. This di- 
sease, also called ‘‘canker’’ 
and ‘‘black-scab’’ is caused 
brown sclerotia upon the seed tubers; 
these are largely controlled by seed 
treatment with formaldehyde or cor- 
rosive sublimate. (See bulletins 139 
and 145). 
Potato Scab is a well known para- 
sitic disease of the potato tuber that 
needs no extended description. Whether 
due to fungi or bacteria, or both, the 
practical prevention of potato scab con- 
sists in destroying the parasites on the 
seed potatoes and then in planting 
them in soil free from those organisms. 
The organisms in question will usually 
be found in soil on which potatoes were 
grown the previous year, or in that 
freshly manured. The materials used 
by this Station in treating for scab are 
two, namely, solution of corrosive sub- 
limate and solution of formalin, as per 
strengths given in spray calendar. It 
is ineffective to treat the seed and 
then plant on scab-infested land. See 
also Wart-disease. 
Fig. 85. Sases of potato stems showing lesions caused by 
Rosette Fungus. The shaded areas were dark with an 
abundance of the fungus, and the tops showed conspicuous 
Rosette effects. From Bulletin 139. 
by a soil infesting fungus, (Chrysophlyctis endobiotica Schilb) and has recently 
’ become established in New Foundland and possibly at other points in North 
