shows in foliage color, ranging from dark greenish bronze to light orange,
in defoliation, and sudden death of branches. Other root nematodes include the sting nematode, a major pest of strawberries, celery, and corn
in Florida; citrus root nematode is troublesome in California on olive
as well as citrus; and root lesion nematodes are pests of narcissus and
Control. Although D-D mixture and ethylene dibromide will kill root
nematodes in soil, they cannot be used near living plants. Parathion
effectively kills nematodes in soil around boxwood without injuring the
host. Shrubs with root system reduced by nematodes need careful watering.
ROOT-KNOT NEMATODE (Meloidogyne spp.).
There are at least 5 species of
the nematode which causes round nodules or long irregular swellings in roots of more than 1400 different plants-all types except grains
and grasses. Affected plants are stunted, often wilt, turn yellow, and die.
The larvae develop to maturity inside the root gall. The female is pearshaped, white, and glistening, can sometimes barely be seen as a white
dot (Figure 41 A). She extrudes a sac full of brownish eggs, and under
the microscope larvae can be seen coiled up inside the eggs. After hatching, the larvae move from a decaying knot to a new root or another
location on the old, secreting a chemical which induces swelling. On
legumes you sometimes have difficulty distinguishing between nodules
formed by beneficial bacteria and root knot, but the former can be readily broken off while the latter are part of the root and cannot be removed.
In warm weather a generation is completed in a month, in cool weather
it takes 2 months, and below 55°F. all activity stops. This is the reason
root-knot nematodes are more of a problem in the South. Adults cannot
live long outside the gall, but larvae and eggs survive some months, possibly 2 years, in soil without a host plant. They are distributed in nursery
stock, root crops, in seedlings like tomatoes that are started in the South
and shipped North, and on tools and equipment. They flourish best in
light sandy soils.
Control. Soil fumigation is most effective but can be practiced only on
fallow soil. D-D mixture is much used in commercial operations, sometimes chloropicrin, tear gas, and ethylene dibromide is favored for small
gardens. It is available as Garden Dowfume and also in capsule form,
Soilfume-Caps. Rigid exclusion, refusing all seedlings or nursery stock
with knots or galls on the roots, is necessary. If you dig up a sick plant
in your garden, burn it and if possible treat the soil before replanting.