EARTH-KIND NEMATODE CONTROL
If you have nematodes in your garden sooner or later they will decrease
or end production. Nematodes will severely damage all garden crops except
corn, onions, garlic and nematode- resistant tomatoes. Even these nematode-tolerant
crops will be adversely affected if a severe nematode population is present.
How does one know if nematodes are a problem in their garden? Above ground
symptoms of nematode infestations are similar to many other root diseases
or environmental factors limiting water and nutrient uptake. These symptoms
consist of wilting during periods of moisture stress, stunted plants, chlorotic
or pale green leaves and reduced yields. Most characteristic symptoms are
those occurring on underground plant parts. Infected roots swell at the
point of infection and form knots or galls. Several infections may occur
along the same area resulting in large fleshy galls. The appearance of the
galls will depend in part upon the plant being affected and the nematode
species involved. Fast growing annuals will have a large fleshy gall and
woody perennials, small hard galls. Infected roots are retarded in growth
and lack fine feeder roots. Rotting of roots develop late in the season.
When tubers, corns or other edible root portions are infected, small swellings
or pimpling is evident on the surface.
Vapam was the most effective nematicide available. Unfortunately, the chemical
control for nematodes named Vapam is no longer available. Organically, only
the planting of cereal rye (Elbon) in the fall to grow during the winter
will decrease nematode populations. Excessive drying of the soil during
July will also help. Another possible solution may be the solid planting
of marigolds for 3 months in areas heavily contaminated with nematodes.
The
marigold, when grown on soil infested with nematodes, suppresses the population
of these nematodes and reduces the numbers found in the roots of susceptible
host plants. Three compounds of an a-terthienyl type, toxic to nematodes,
have been identified in root exudates from these plants. Terthienyls are
released from growing roots, even without their decay, but benefits require
three to four months to become clear. There is some evidence that a-terthienyl
is inhibitory to some plant-pathogenic fungi too. Marigolds also function
as a trap crop since larvae which penetrate the roots do not develop beyond
the second larval stage and do not lay eggs.
Marigolds have never been used for a biological nematode control because
Vapam was less trouble-some and more economic. Since Vapam is no longer
available and since cereal rye does not survive in hot weather, use of the
marigold for nematode control must now be examined. Of course, you
will want to follow proper planting procedure. Marigolds perform best if
planted in a well drained location which receives at least 8-10 hours of
sun daily. Incorporate generous amounts of organic material (pine bark mulch,
peat moss, or compost), or fill with a commercially available landscape
mix. Then add slow-release lawn fertilizer (no herbicide, please!) at 2
pounds per 100 square feet. Soak the bed immediately after transplanting
and, depending on the weather, irrigate when the soil becomes dry and the
plants begin to wilt slightly. (CAUTION: DO NOT keep these plants wet after
they become established! Keep the soil feeling slightly moist to the touch
but not wet. Continuously soggy, wet soil in the planting bed will stunt
MARI-MUM growth and eventually kill them.)
Buy transplants which are completely green or those that are just forming
buds. Transplants covered with open blossoms will not produce the normally
expected growth after planting. Bloom removal and/or fertilization WILL
NOT overcome the detrimental affects of transplanting a MARI-MUM in full
bloom. MARI-MUMS are among the most durable of transplanted annuals and
are also the easiest to transplant. Unlike impatiens, begonias, petunias
and bluebonnets, MARI-MUMS cannot be planted too deep. Other annuals rot
if planted too deep; MARI-MUMS root. In fact, many times roots can be seen
on the stems of transplants when purchased at nurseries. Transplanting depth
does not affect ultimate plant height. Because of this never-too-deep transplanting
phenomenon, large, leggy transplants can be salvaged by planting deeper
to provide support during establishment.
The name marigold conjures up thoughts of pests. Some people think marigolds
repel certain pests while other folks fear the devastating spider mite which
the beautiful flowering plants seem to attract. Marigolds DO NOT repel rabbits,
other rodents or deer. Marigolds also don't repel insects; in fact, they
are attacked by and shelter the formidable spider mite.
So why should anyone who fears a spider mite invasion plant MARI-MUMS? MARI-MUMs
are recommended for transplanting in August because spider mite populations
decline in cooling fall temperatures. The optimum temperature for spider
mite reproduction is 97 degrees F. during which the mite population can
double every 5 days. As fall temperatures cool to 77 degrees F., mite populations
require as many as 20 days to double. Because mite populations are virtually
eliminated when planting beds are renovated for MARI- MUM establishment
in August and since mite populations do not have an adequate time of favorable
temperatures to regenerate their masses, spider mite damage to fall MARI-MUM
plantings is minimal, even without a single pesticide application!
MARI- MUMS ARE NOT spider mite resistant; the lack of mites on fall plantings
is merely a function of temperature and population control. Interested
gardeners who have a nematode infested area should transplant marigolds
12 inches apart in August and allow them to grow there until fall planting
of cole crops begins in October. Tops of the marigolds should then be removed
and the root system tilled into the soil. By using marigold in the summer,
you can rid the planting area of those devastating nematodes without endangering
yourself or the environment, a truly EARTH-KIND practice.¶