Cultural Practices for Root-Knot Control


 The dates of listing before October 1 for each year were as
 follows: July 30, August 18, September 9 and 22, 1937; July
 11, August 4 and 18, September 5 and 19, 1938; July 6 and 24,
 August 3, 14 and 22, September 1, 12 and 25, 1939; July 26,
 August 8 and 23, September 9 and 23, 1940. During the months
 of October to January the interval between listings was gradually
 lengthened to about 2 months.
 The method of listing the soil during periods of clean fallow
 is shown in Fig. 6. The balk left in the furrow served to in-
 crease the effects of aeration and drying. The balks were plowed
 each time before the soil was rebedded.
 Tobacco crops of the Rg variety were grown each year and
 harvested, cured, sweated and graded according to usual com-
 mercial practices.
 After the crop was harvested a representative sample of the
plants from each plot was pulled and examined for root-knot,
and the plants were placed in 5 groups to which were assigned
the following numerical values: None, 0; very slight, 10; slight,
20; medium, 60; and heavy, 100. The average value for the
plot was the root-knot index, a measure of the amount of root-
knot infection.
 The grade index was the average value per pound, calculated
from the yield of leaves in each grade and the comparative
values of the grades. This served as a measure of leaf quality.
 The crop index was obtained by multiplying the yield in pounds
per acre by the grade index. The crop index was a measure of
the total value of the crop.
 Daily minimum and maximum air temperatures and rainfall
were observed about 100 yards from the plots. During the first
2 years of the experiment daily minimum and maximum soil
temperatures were measured by means of registering ther-
mometers; readings were taken at depths of 1 and 4 inches
about 100 feet from the plots in the same shade.

 RESULTS
 Table 1 gives the root-knot index, yield, grade index, and crop
index for each treatment in each of the 4 crop years. The results
are averages for the 4 plots of a given treatment. For con-
venience in comparing the results of the various years the yield,
grade index and crop index are also calculated on a comparative
basis, using a value of 100 percent for the results of Treatment
3 each year.