Florida Agricultural Experiment Station


large investment which he must make in shade structure and
heavy fertilization, and from the superior quality of tobacco
which he could usually produce on old shades in continuous
production.
 The root-knot disease is caused by small eel worms or nema-
todes (Heterodera marioni Goodey) which enter the root tips
of tobacco or other host plants and live there. The activities
of the worms cause the roots to swell into the form of knots or
galls (Fig. 3), and the entire plant becomes more or less yel-
lowed and stunted and more subject to wilting during periods
of dry weather or hot sunshine (Fig. 1).











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 Fig. 3.-Roots of a cigar-wrapper tobacco plant heavily infected with
 root-knot nematodes.
 A female nematode matures at the age of 3 weeks or more,
 depending on the temperature, and lays hundreds of eggs, which
 are sometimes held together in masses by a gelatinous material.