HomeMy WebLinkAboutClinton News-Record, 1977-04-14, Page 39By Robert Hall, Associate
Professor
Department of Environmental
Biology
Ontario Agricultural College
University of Guelph
Seed decay, damping -off and
root rot are very common
diseases of crop plants and are
difficult to control. The disease
organisms hide in the soil and are
difficult to get at. Control of these
diseases is generally attempted
by using resistant plants, when
these are available and suitable,
or by using disease-free or
chemically treated seed, planting
material and soil. In many cases,
. these. conditions cannot be met
adequately and root diseases
continue to be a problem.
A promising new line of in-
vestigation is called 'biological
control. It makes use of living
organisms to control other
organisms which cause disease.
Soil contains an abundance of
microorganisms. In some cases,
populations of disease organisms
(pathogens) in the soil or around
plant parts in the soil can be
reduced by tipping the balance of
• power in favor of certain other
organisms. These organisms
4 may eat pathogens, or compete
with them for space and food, or
suppress their growth by
producing antibiotics or en-
zymes. °
Certain diseases, sucks as
potato scab, bean root rot and
banana wilt, cannot develop in
some soils. In some of these
cases, for example potato scab,
this natural protection against
disease is known to be due to
microorganisms in the soil. The
• trick is to know how and when to
tip the balance in favor of the
good guys so that plants can be
protected.
An outstanding example of
success comes from studies'of a
for
disease.
Page 17
• Biologicalcontrol coming
and food that the disease fungus
is unable to grow in the stump
and therefore cannot 'spread to
nearby trees.
Many attempts have been
made to manipulate populations
of organisms in the soil by adding
mulches. Sometimes disease is
reduced because the mulch
favors the growth of
microorganisms antagonistic to
disease organisms. But in other
cases, disease is increased
because the disease organism
multiplies on the mulch. So there
is much yet to be learned about
Take nasturtium
to lunch
Nasturtium blossom of the "single"
type
Few people can say the word "nas-
turtium" without smiling because
it is an endearing little flower.
Long stemmed, faintly fragrant,'
brilliantly colorful, nasturtiums
rank number four in popularity
polls. Perhaps, if more gardeners
knew that nasturtiums really are
good to eat, they would rate even
higher.
Nasturtiums are members of the
same plant family as a number of
leafy vegetables including cress
and mustard greens. Buds and
flowers are tender and piquant,
perfectly safe to eat in salads.
If eating nasturtiums doesn't
appeal to you, thengrow them to
arrange, wear in lapels, or enjoy in
the landscape. White, red, cherry,
orange, mahogany, gold and yel-
low separate colors and excellent
color mixtures are available from
seed displays; mail order catalogs
also offer varieties with variegated
foliage or extra dwarf plants.
Nasturtiums are -customarily
spring -planted in warm soil. The
seeds are very large and sprout
rapidly; blooms appear within 45
to 50 days.
The old adage about nastur-
tiums preferring poor soil is true;
too much water and fertilizer
makes them excessively leafy. In
hot climates, the plants will survive
longer if planted in locations that
receive afternoon shade ... else-
where, full sun is preferable.
Aphids (plant lice) can be a
problem on the undersides of
leaves. Shredded tobacco scattered
on the soil will serve as a deterrent,
or nicotine sulphate sprays.
root rot of forest trees in
England. The disease is favored
' by leaving stumps of felled trees
in the ground. The fungus causing
the disease lands on the stump
surface, grows through the
stump, into the roots, and from
there enters the roots of trees
growing nearby. Stumps are
expensive to remove. A simple
and effective biological control
was developed in which the
freshly cut stumps were painted
with another fungus that grows
rapidly over the surface of the
stump. It takes up so much space
biological control.
There is no doubt that farming
practices such as crop rotation
and plowing dead or living plant
material into the soil profoundly
affect the numbers and types of
microorganisms in the soil.
Practices such as these which
lead to good crops do so partly
because they result in biological
control of disease. As we learn
more about how this happens, we
can more rationally develop
management practices which
control plant disease.
For example, farmers in
California found that when dry
barley straw was incorporated
into the soil, bean root rot was
decreased. Scientists sub-
sequently found that the barley
straw literally starved to death
the fungus causing the disease,
by temporarily locking up the
nitrogen in the soil. Research into
biological control is stimulating
interest because it has the
potential to reduce the amounts
of pesticides added to the en-
vironment while providing
stable, long-term plant disease
control.
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