Nematodes are microscopic roundworms. There are both good and bad nematodes. Many nematodes live in our soils and are
beneficial. But there are a number of
harmful species that attack plants. These nematodes insert their stylet mouth-part, much like a hypodermic
needle, into the tissue and suck out the plant juices.
Plants which are infested with nematodes may exhibit symptoms of stunting, yellowing and wilting. Further symptoms may be smaller and fewer leaves, and smaller fruit. Also, due to this feeding, the root knot nematode, in particular, will cause the plant cells to rapidly enlarge, thus developing characteristic bumps or knots on the roots.
What to do? If root knot nematodes are in your garden, take it seriously. Eradicating the garden of nematode pests is highly unlikely, but they can be managed with good sanitary procedures. Here are some measures:
·
Apply organic matter (OM) to the soil. OM will encourage the growth of beneficial
organisms, fungi, bacteria and good nematodes. They, in turn, will ‘attack’ the plant parasitic nematodes and deplete
their numbers. A note of interest, there
is one species of fungus that forms loops with its fungal threads. Nematodes will become stuck in these loops,
which will actually tighten, and eventually the nematode dies.
·
Crop rotation
Do not replant the same crop or any susceptible crop into infested soil. For instance, if you discover root knot
nematodes on your cucumbers, plant a resistant crop, like garlic or corn, in
place of the cucumbers. For best
results, do not plant with a susceptible crop for 3 years.
·
Keep the soil fallow. A more drastic form of
crop rotation is simply keeping the infested area fallow. This starves the nematodes. Do not allow any
crop, even weeds to grow there. But do add organic matter. Again, 3 years is
best.
·
Soil sterilization This involves covering the
infested area with a piece of clear plastic for at least one month and
preferably two. This should be done
during the hottest part of the year. In
hot climates with clear skies, enough heat can be produced underneath this tarp
to kill most of the nematodes.
·
Plan resistant varieties. The best control
against nematodes is to use resistant varieties. You may notice on a tomato
seed package the letters VFN. This means
that the variety is resistant to the fungus, Verticillium and Fusarium
and to the root knot nematode. Such
varieties include Celebrity and Better Boy. Asparagus, corn, garlic, onion, strawberry, zinnia, salvia and marigolds
are also resistant to root knot nematode.
Most Important: DO NOT SPREAD CONTAMINATED SOIL
Perhaps the most important aspect of controlling nematodes
is to stop them from spreading throughout the garden. If your tomato patch is newly infested with
nematodes, keep those nematodes there. Nematodes will slowly spread in the soil
by themselves. Don’t help them by
carrying soil from the infested area to other areas, or by carrying around
contaminated dirt clinging to garden tools and shoes. Work in an infested area last. Always clean tools
and shoes. Be cautious when receiving
potted plants from other gardens or even from a nursery that has non-sterilized
soil.
Marigolds have
been reported for many years as a way of reducing the nemotode populations. The
French marigolds are most effective; varieties include Nemagold, Petite Blanc,
Queen Sophia, and Tangerine. Unfortunately,
planting a few marigolds next to each susceptible plant will NOT eliminate the
problem. To be effective, the entire infested area needs to be planted in
marigolds, each plant about 7 inches apart. The flowers must be planted for a minimum of two months and then turned
under. The area also needs to be kept free of weeds. Then, root knot sensitive
plants can be planted back into that area the following planting season. Replanting
marigolds every other year will almost certainly be necessary.
