It should be remembered that the treatment will do but little 
good if the soil to be planted is already infested with scab or 
black-leg from former crops. The fact that some of these dis- 
eases may live over in the soil for three years or more, gives us, 
in fact, one of our main reasons for rotation of crops. 
Seed disinfection with corrosive sublimate (mercuric chloride). — This 
treatment is more effective than formaldehyde for the Russet Scab, 
or Black Scurf, disease of the tubers. They should be soaked 1J 
hours in a solution containing 4 ounces of the corrosive sublimate 
(which is very poisonous) in 30 gallons of water. First dissolve 
the powder in a quart or two of warm water, then add to the 
rest of the water. Do not use metal containers, as the solution 
combines rapidly with metal and thus loses its efficiency. 
Spraying. — Bordeaux Mixture is the standard spray material 
for potatoes, especially for the dreaded late-blight. It was dis- 
covered more or less accidentally in 18S2 by Professor Millardet, 
of Bordeaux, that a mixture of milk of lime and bluestone made 
grape-vines on which it was sprinkled more resistant to mildew. 
It had been the custom in certain vineyards in France to sprinkle 
a few rows of vines near the road with this mixture, in order to 
give them a poisonous appearance to scare off the hungry passers- 
by; and Professor Millardet, noticing that these sprinkled plants 
were healthier, begun to experiment, shaking the Bordeaux Mix- 
ture on to the plants with a broom. 
One of the most interesting things about Bordeaux Mixture 
so far discovered is that it has, aside from its fungicidal power, 
much value as a stimulator of plant activities. The sprayed 
potatoes are greener and remain alive longer than unsprayed 
vines. Even though late-blight, early-blight and tip-burn be not 
in evidence, spraying has been found to pay, for this other 
reason. 
The spraying should begin when the plants are about 6 to 8 
inches high, or wffien the eggs of the first brood of potato bugs 
begin to hatch. From 5 to 8 applications are usually made, at 
intervals of 10 days to 2 weeks, depending on the weather condi- 
tions; from 50 to 75 gallons to the acre being required at first; 
later, from 100 to 150 gallons. 
To make Bordeaux Mixture (4 — 4—50) — Copper sulphate, 4 lbs; 
quick lime, 4 lbs; water, 50 gallons. (Add 3 lbs. lead arsenate to 
kill insects). 
Dissolve the copper sulphate by suspending in a coarse bag 
over night in 25 gallons of water. Slack the quick lime in a small 
amount of water (4 gallons, e. g.), and stir when fully slacked 
into 25 gallons of water. Pour the two solutions together, stirring 
constantly, through a strainer into a barrel or vessel holding 50 
gallons. Sprav at once, as the Bordeaux Mixture loses much of 
its efficiency within a few hours. 
Those who have much spraying to do are advised to make up 
stock solutions of the two ingredients, which keep indefinitely — 
at the rate of 1 lb. to 1 gallon of water. 
