INJURIOUS INSECTS OF I90Q AND IQIO. 169 
after the tubers are stored. Only clean, healthy tubers should be 
selected for seed, and spraying should be conducted as for early 
blight, except that when spraying for late blight alone, it may be 
begun later in the season. 
Scas: Affected potatoes show rough, corky patches which may, 
in severe cases, be cracked. The yield may be somewhat affected, 
but a greater loss is due to the decreased value of potatoes. It is 
ncessary to remember that beets and turnips are susceptible to the 
same disease and that the disease persists not only on the tubers, 
but also in the soil. No susceptible crop should be planted on in- 
fected land for at least three years and preferably longer. Seed 
potatoes should be soaked for two hours in formalin used at the rate 
of I pound to 30 gallons of water. The tubers may then be dried, 
cut and planted. They should not again be brought into contact 
with anything which contained them before they were treated. 
Thirty gallons will usually treat about 45 to 50 bushels of potatoes. 
Corrosive sublimate may also be used, but, on account of 1ts poison- 
ous nature, is not so desirable as formalin. 
Tip Burn: This is a disease which is not induced by any 
parasitic organism. The tips of the leaves dry and break off during 
hot, dry weather, especially if the crop is on light soil. 
Wi_tT—INTERNAL Brown Ror: The disease is caused by a 
fungus which may live in the soil and gain entrance through the 
roots. The vines wilt, and, when pulled up, the roots usually 
break off very easily. The disease may be in the tubers at harvest 
time without showing conspicuous symptoms. However, when 
stored in warm places where considerable moisture 1s present, it 
may spread very rapidly, at first forming a yellowish or black ring 
near the stem end; and later the entire interior may be converted to 
a dry, shrivelled mass. Bacteria also very often gain entrance and 
aid in the rotting process. Potatoes from wilted vines are very 
liable to be infected, so they should be examined and if they show a 
brown discoloration beneath the surface of the stem end, they 
should be used at once, as at this stage they are not unfit for eating. 
In any case, tubers should be stored in a dry, cold place. 
In controlling the disease, affected vines should be removed and 
destroyed, no affected tubers should be used for seed, and crop rota- 
tion should be practiced. It is not definitely known how long soil 
will remain infected, but it is probable that several years will be 
