NEMATODE CONTROL AND THE BEST ORGANIC
This December (2006) marks the 27th anniversary
introduction to Texas' gardeners of the best organic nematode
control as well as a wonderful source of clean organic matter.
On December 2, 1979, I wrote the first column about the use
of cereal rye (Elbon) as a control for nematodes and as the
fastest growing, cold-hardiest grass that can be used as a "green
manure" crop for South Texas. Malcolm Beck introduced me
to cereal rye as a cover crop. I was amazed by the growth rate
and then was delighted to have Dr. Jerral Johnson, Texas A&M
Extension Plant Pathologist, find quantities of scientific literature
revealing it is one of the best trap crops for nematodes. All
of these beneficial qualities of cereal rye were proclaimed
to gardeners every year beginning in 1979 and ending in 1992
when I stopped writing for the newspaper. Columns were used
such as: http://www.plantanswers.com/garden_column/110301/110101.htm
George Wechsler of Wolfe (now Calloway's) Nurseries and all
privately-owned nurseries stocked and sold thousands of pounds
of this beneficial product yearly.
Nematodes are unsegmented roundworms, different
from earthworms and other familiar worms that are segmented
(annelids) or in some cases flattened and slimy (flatworms ).
Nematodes living in soil are very small and most can only be
seen using a microscope. There are many kinds of nematodes found
in the soil. Most of these are beneficial, feeding on bacteria,
fungi, or other microscopic organisms. There are even nematodes
that can be used as biological control organisms to help manage
important turf insect. Unfortunately, the effectiveness of applications
of beneficial nematodes is so extremely dependent on precise
soil conditions and favorable environmental conditions that
positive results which are actually caused by the beneficial
nematodes are seldom achieved. There are also a group of nematodes
that feed on plants -- these are called plant-parasitic nematodes.
All plant-parasitic nematodes have a stylet or mouth-spear that
is similar in structure and function to a hypodermic needle.
The nematode uses the stylet to puncture plant cells, and then
inject digestive juices and ingest plant fluids through it.
The results can be seen at: http://www.plantanswers.com/tomato_root.htm
When the cereal rye was first introduced to the
market, it was mainly recommended as a wonderful source of green
manure organic matter. The nematode control aspect was just
a favorable side effect which organic gardeners could enjoy.
That was when home gardeners could purchase soil nematicides
such as Vapam and Nemagon. Since then, a television segment
on Sixty Minutes revealed that some factory workers were sterilized
when manufacturing Nemagon so my wife purchased all available
supplies. Neither of these products nor any effective nematode
control products are now available to the home gardener.
After several years of gardening and growing susceptible plants,
nematode populations increase to the point that damage becomes
noticeable. Control practices include summer fallowing, rotation,
adding organic matter, planting trap crops, removing diseased
plants and using resistant varieties. There are few resistant
varieties available and summer fallowing as well as rotation
is impractical in a small home garden. The planting of cereal
rye at this time of the year utilizes the control measures of
planting a trap crop and adding organic matter. All these control
measures are designed to reduce the soil's nematode population-none
of these measures completely eliminate the entire population.
Cereal rye can be planted by merely seeding directly on top
of the garden soil and raking in. Apply seed at about the rate
of 3/4 to one pound per hundred square feet of garden area to
insure good coverage and adequate growth. Raking to give seed
some coverage by soil helps. Be sure to water the rye regularly
and fertilize with any type of fertilizer every three weeks
for maximum growth. Remember that most of the organic material
produced is in the root system rather than the top foliage.
Shred rye and till the soil one month before planting is to
occur so the massive rye root system will have adequate time
High soil organic matter alone does not insure
root knot nematode control. The higher the organic matter, however,
the better the chance that antagonistic organisms will develop.
Some soil fungi trap nematodes and use them as a food source.
Some organic matter works better than others. Turning under
a green manure crop such as small grains (cereal rye) or legumes
(vetch) several weeks before planting is the best. Additional
nitrogen may be necessary for adequate crop production because
decay organisms in the soil use available nitrogen as they break
down the green manure crop. Also, remember the information presented
in "The Truth About Microbes" at: http://www.plantanswers.com/microbes.htm
which stated: "The overall effect of fertilizer applications
is to markedly increase microbial numbers and activity in soil
through increased plant growth. The majority of soil microbes
require organic carbon to grow and produce new cells. In grass
systems, the vast majority of organic matter is produced from
decomposing roots and leaves. Fertilization increases the amount
of organic substrates available to soil microbes by increasing
its source, the grass plants themselves. Thus, rather than producing
"dead soil", judicious use of fertilizers invigorates
soil microbes by allowing plants to produce more resources for
Sometimes people resort to home remedies to control
nematodes such as planting marigolds or mixing sugar or lye
into the soil. Of these three, only dense populations of marigolds
are effective in controlling nematode populations. Marigolds
secrete toxic compounds of an a-terthienyl type into the soil
which kills nematodes but planting a few marigolds around annual
plants in infested soil will NOT prevent infection. Marigolds
also act as a trap crop. Nematodes enter their roots but are
unable to complete their life cycle. Trapped nematodes die without
reproducing. To be effective marigolds must be planted as a
solid crop and grown for 90 days to begin secreting the three
compounds of an a-terthienyl type to reduce the nematode population.
See the write-up at:
It has been brought to my attention recently
that nematodes can also damage turfgrass-especially in sandy
soils. Plant-parasitic nematodes are probably the least understood
and most difficult to manage of the turfgrass pests in Texas.
As plant-parasitic nematodes feed they damage the root system
and reduce the ability of the grass to obtain water and nutrients
from the soil. Roots may be abnormally short and appear darkened
or rotten when damaged by plant-parasitic nematodes. Root galls
or knots associated with certain nematode damage to other crops
are not always evident on grasses. When nematode population
densities get high enough, or when environmental stresses such
as high temperatures or drought occur, above-ground symptoms
may become evident. Symptoms include yellowing, wilting, browning,
thinning out, or death. Often weeds such as spurge and sedges
become prominent as the grass thins out . Nematode damage usually
occurs in irregularly shaped patches that may enlarge slowly
over time. Be aware that similar conditions may be caused by
other factors such as localized soil conditions, fungi, or insects.
Because plant-parasitic nematodes live in soil or roots, the
pesticides used to kill them tend to be very toxic and are water
soluble. Because of health risks and environmental concerns
there are currently no toxic nematicides that are labeled for
use on established home lawns. There are a number of products
available for use on home lawns that are marketed as "organic",
"biological" or "non-toxic" that claim to
be suppressive to plant parasitic nematodes. Be aware that in
order to be labeled for home use these types of products need
to be safe, but do not need to be proven effective. Nernatologists
at numerous universities have tested many of these products
for efficacy, generally with disappointing results.
Adding soil amendments can help the grass tolerate nematode
damage or possibly suppress nematode population densities. Remember
that anything that can he done to improve root health is good.
Colloidal phosphate incorporated into fine sand has been shown
to help bermudagrass withstand attack by certain nematodes.
Organic materials such as composted municipal sludge or manures
can also promote grass health, and at the same time may stimulate
fungi that attack nematodes.
Some of the best practices for managing nematode damage in home
lawn include avoiding other stresses on the grass. Grass that
is given proper watering and fertilization can often withstand
higher levels of nematode infestation than grass suffering from
drought or nutrient deficiencies. Over-fertilization should
also be avoided, too much nitrogen can stimulate the production
of succulent roots that are more susceptible to nematode damage.
Grass that is mowed too low, or that is allowed to grow too
tall between mowing, is also more prone to succumb to nematodes.
Frequent mowing at moderate height is best. While minimizing
these stresses can help, even the best managed lawns can suffer
from nematode damage from time to time.
At present, the best management strategies for nematodes in
the home lawn are aimed at increasing the grass' ability to
tolerate nematode damage. These strategies include avoiding
stress and promoting root vigor.