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iologicalCotrof cow� g
for crop diseasesPeg* 17
By Robert Hall, Associate
essor
epartnrent of Environmental
lob
ntarlo Agricultural College
University of ueIphand
ed decar, re veryy common
sesof
tatacrop plants and are
cult to control. The disease
msms hide Control of these
t soil
ult to get
ales is generally attempted
using resistant plants, when
eare available and suitable,
by using disease-free or
ically treated seed, planting
erial and soil. In many cases,
e telt' and roototdseases
e met
uately
ince to be a problem.
promising new line of in-
igation is called biological
roL It makes use of living
nisms to control other
nisms which cause disease.
contains an abundance of
oorganisms. In some case$,
ations of disease organisms
ogens) in the soil or around
t parts in the soil can be
ced by tipping the balance of
r in favor of certain other
nisms. These organisms
eat pathogens, or compete
them for space and food, or
ress their growth by
ucing antibiotics or en -
es,
rtain diseases, such as
to scab, bean root rot and
a wilt, cannot develop in
soils. In some of these
for example potato scab,
natural protection against
is known to be due to
rganisms in the soil. The
is to know how and when to
e balance in favor of the
guys so that plants can be
ed.
outstanding example of
ss comes from studies of a
e nasturtium
lunch
G
01
turtium blossom of the "single"
people can say the word "nas-
um" without smiling because
an endearing" little flower.
g stemmed, faintly fragrant,
iantly colorful, nasturtiums
number four in popularity
Perhaps, if more gardeners
,that nasturtiums really are
to eat, they would rate even
asturtiums are members of the
e plant family as a number of
vegetables including cress
mustard greens. Buds and
ers are tender and piquant,
ectly safe to eat in salads.
eating nasturtiums doesn't
al to you, then grow them to
nge, wear in lapels, or enjoy in
andscape. White, red, cherry,
e, mahogany, gold and yel-
separate colors and excellent
mixtures are available from
displays; mail order catalogs
offer varieties with variegated
ge or extra dwarf plants.
asturtiums are customarily
gplanted in warm soil. The
are very large and sprout
ly; blooms appear within 45
days.
e old adage about nastur-
preferring poor soil is true;
much water and fertilizer
es them excessively leafy. In
limates, the plants will survive
r if planted in locations that
ve afternoon shade , , else -
e, full sun is preferable:
hids (plant lice) can be a
em on the undersides of
.Shredded tobacco scattered
e soil will serve as a deterrent,
:otine sulphate sprays.
root rot of forest trees in
Englaftd. The disease is favored
by leaving stumps of felled trees
ilthe ground. The fungus causing
to 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 devbloped 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
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
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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