Cultural Practices for Root-Knot Control


TABLE 2.-GENERAL OBSERVATIONS ON ROOT-KNOT CONTROL EXPERIMENT
 BY CROP YEARS, WITH PARTICULAR REFERENCE TO TREATMENT 3, FALLOW
 FOLLOWED BY OATS.
 S FALL SEASON I CROP SEASON
 CROP I Tempera- I Dat of I Root-Knot Grade
 YEAR Rainfall ture Setting Rainfall Index* Yield Index
 1937-1938 above normal low IApril 1 normal medium high fairly low
 1938-1939 low high Mar. 31 normal** low low high
 1939-1940 low moderate April 10 normal low high low
 1940-1941 low low April 18 lowt medium medium low
 High at beginning of experiment.
 ** Excessive during harvesting period.
 t Normal during harvesting period.

 Table 2 gives general observations on the results by crop years,
with particular reference to Treatment 3, fallow followed by
oats. The root-knot index was high at the beginning of the
experiment, fell to medium for the first year, dropped to a low
reading for the second, remained low for the third and rose to
medium for the fourth. The 1938 fall season, which gave a
striking reduction in root-knot, had low rainfall and high tem-
perature, both favorable to root-knot control, as will be men-
tioned again in the discussion of the results. The 1940 fall
season, which gave an increase in root-knot, had low rainfall
but the temperature was also low.

 DISCUSSION

 Treatment 3, fallow followed by oats, gave slightly the best
4-year average yield of the 3 treatments which were continued
throughout the experiment. Results of this treatment are used
as a basis for evaluating results of other treatments.
 Treatment 2, fallow only, gave a little less root-knot 3 years
out of 4 than Treatment 3; the quality was about the same.
Yield and total value were highest of all treatments the first
year and then steadily declined in relation to those of Treat-
ment 3. This decline was probably due to a gradual depletion
of the organic matter reserve in the soil.
 Treatment 1, which differed from Treatment 2 in having the
tobacco roots removed from the field, gave slightly poorer re-
sults than Treatment 2 but the difference was within the limit
of experimental error. After 2 years the original Treatment 1
was discontinued and a cover crop of Otootan soybeans was sub-
stituted; these were moderately infected with nematodes and
root-knot in the succeeding tobacco crop showed a considerable
increase. The last year of Treatment 1 a few cockleburs
(Xanthium sp.) were grown to maturity and all other vegeta-