Aug. 15, 1925 
Soil Disinfection for Potato Wart 
359 
cations made in the earlier chemical treatments gave very erratic 
results, the minute quantities of chemical breaking down, leaching, 
or forming new combinations in the soil. This is due in part, as are 
the fluctuations in the 100 treatments made at Sandy Run in 1921 
and here summarized, to the nature of the available gardens. In no 
case has the soil been uniform throughout a garden, but has varied in 
composition by reason of mixtures due to stripping and coal-mining 
operations, addition of soil from the woods, the dumping of ashes and 
garbage, and unequal applications of manure. By distributing the 
treatments among these variable areas, 14 however, it is believed that 
the results more truly represent the comparative effects of the various 
chemicals used, even though they are less uniform than those ob¬ 
tainable by selecting contiguous beds for several applications of like 
chemical. Prior to the use of chemicals, and again before planting 
each of the two following seasons, the ground was thoroughly spaded 
to the depth of 8 inches. 
Soil treatments were applied dry or in solution as indicated in 
Table XXI. The chemicals applied dry were powdered to permit 
even distribution. Watering cans with rose tops were used for apply¬ 
ing liquids. Two methods of application were used; either addition 
to the surface of the area treated, or mixing with the soil to a depth 
of 8 inches by spading. 
Planting followed treatment after 10 days or less the first year, 
while no further treatment other than spading and cultivation was 
given the second and third years. 
The tolerance of the potato plant for the chemicals used is ex¬ 
pressed by the symbols indicated in the footnote of Table XXI. The 
stand, the growth of tops, and the yield of tubers are all taken into 
account in determining the rating. The data presented are for par¬ 
ticular soils and conditions and no attempt is made to draw general 
conclusions from them. It is of interest to note that of these chemi¬ 
cals Bordeaux (pi. 1, D) in whatever concentration or amount tried, 
potassium permanganate in its higher dilution, and a proprietary 
compound called Qua-sul apparently were not injurious to growth in 
any year. 
Carbolic acid and the weaker treatment with chloride of lime 
(pi. 1, A) showed poor growth or none in the first year and practically 
normal growth in the second and third. The heavier applications of 
chloride of lime exhibited residual toxicity the second year. Treat¬ 
ments with sulphur produced the reverse condition. During the first 
season the plots which had received 0.12 pound of sulphur per square 
foot made a normal growth of tops, while the 0.25 and 0.3 pound 
{ dots made poor and very poor growth, respectively. The tops died 
ater in the season because of the increased soil acidity. A consid¬ 
erable number of tubers had formed, but owing to the death of the 
tops these remained very small. In the second and third seasons, 
except for a few burned sprouts in the weakest treatment, all plants 
were killed (pi. 2, C). In the process of oxidation the sulphur had 
increased the soil acidity beyond the limit of tolerance of the potato 
plants. 
Copper sulphate (pi. 1, D), lime-sulphur (pi. 2, A), sodium car¬ 
bonate, sodium chromate, sodium fluoride, a commercial weed killer, 
and the stronger cleaning solution treatments showed no growth in 
14 Figure 3 shows the distribution of the plots. 
