THE CANADIAN HORTICULTURIST

IN order to be able to study more satis-
factorily the relation of temperature
to moisture and fertility in plant
diseases. we must understand more com-
pletely that plants and human beings
are identical in their resistance to
disease. Given certain conditions each
can combat succesfully any disease. It
is well known that where man follows
nature's rules he escapes disease ; if he
does not he has to pay the penalty. So
it would be with plants if we human
beings had not chosen to interfere, for
our own benefit, with nature's methods.
Seeing that we, forcibly, have done this,
it is necessary that we try to follow as
closely as possible what nature would
have done if we are to retain the right-
ful balance.
If we will recognize each plant as a
child we will get off to a good start in
our work. Nature gives each plant a
definite type of growth with definite
food requirements. Do we study each
closely enough so that we know exactly
what is best for it ? Few of us are
really making a close study of plant
growth and until we do we will make
many and often serious mistakes.
All plants require, largely, four sub-
stances in the soil for their growth :
lime, nitrogen, potash and phosphorus.
Of these lime is not so important as the
others, being really a soil sweetener and
helping to make soluble the other three
for plant use. For this reason we will
consider only three. As with the human
the plant must have a steady supply of
all foods. If some element is lacking it
means that the plant will be weakened
in growth just so much. Supposing
phosphorus were lacking-and it is a
well known fact that it is very deficient
in most soils-what will happen ? The
plant structure would tend to make too
rapid a growth and, if any adverse con-
dition set in, disease would 'quickly
seize the opportunity and the plant.
It is claimed to-day that lack of potash
in the soil is causing considerable
trouble in potato growing and that the
cause of our so-called physiological
diseases can be traced to its absence.
Our experimental work on tomato streak
diseases shows very conclusively that an
application of acid phosphate will stay
to a large extent, the -ravages of this
disease. Onion Blight starts when the
bulb is about one-third grown. Bor-
deaux Mixture has little effect on it.
Experiments show it is not from lack of
potash and phosphorus in the soil. Will
nitrate of soda serve ? It is well known
that it will draw moisture to itself from
the surrounding soil. What little work
has been done so far seems to prove that
it at least will go far toward preventing
the disease.

Many diseases get started in crops
through too great changes in tempera-
ture. This cannot be controlled outside
but under glass it is possible, and here
we find more diseases developing, es-
pecially in the early fall and late spring.
The tendency for most of us is to try
to save coal at these periods and many
of our troubles are directly traceable to
this. While it is well to be sparing of
cost in production, we should never
allow our crops to suffer. The steadier
temperature at which plants can be
grown means a greater return.
Plants for Cover Crops
Some writers have divided the
plants used for cover crops into
three groups: Nitrogen gather-
ers, potash plants, and ordinary
plants.
The nitrogen gatherers are so-
called because during their devel-
opment they take some nitrogen
from the soil air. Consequently
in their decay such plants actu-
ally leave the soil richer in this
element. The clovers, peas, beans,
vetches and alfalfa belong in this
class.
One writer, at least, has spoken
of turnips and rape as being pot-
ash plants, since analyses show
them to contain rather large
amounts of this element. These
plants might be used to advant-
age in orchards where a vigorous
growth of trees indicates that
more nitrogen is undesirable.-
Ohio State University, Reading
Course.
Many also in greenhouse work do not
give sufficient air. Especially is this so
among the newer growers. They seem
afraid to give the plants all the fresh air
possible and generally have to make two
or three failures before they do so. I
was asked the other day why the seed-
lings in a certain greenhouse died each
year ; the trouble was that the man did
not ventilate and the plants burned.
Fresh air will harm no plant as long as it
does not strike directly on the plant.
Excess moisture in the greenhouse
probably gives rise to more diseases than
any other cause. Too many growers
seem to think that the plant can stand
any amount of moisture and then run
the house at either a very high or very
low temperature. Most of the mildew
on lettuce and tomatoes is attributable
to carelessness with either of these
factors.
We are only started on this work, but

Fertility and Other Factors
A. H. MacLennan, Vegetable Specialist, Toronto, Ont.

I

60

so far results indicate that a closer study
riust be made of each of these factors for
each crop. While it is not so easy to
handle this work outside, especially the
temperature factor, still we have control
of two out of the three factors and
nature will take care of the other much
better herself than we could.
Pruning Peaches
W. A. McCubbin, St. Catharines, Ont.
There are two diseases in the peach
that can be materially lessened by care
in pruning; one of these is the Brown
Rot and the other is Peach Canker. In
the case of Brown Rot care should be
taken when the trees are (being gone
over to knock off all the old mummied
fruits which were rotted last summer,
and remain in a dried up condition on
the trees. If left till spring the Brown
Rot fungus which is still alive in these
mununies will start    into growth in
warm weather, and a new crop of
spores will be produced to start infec-
tion once more.
Pruning can also be made to help
greatly in keeping down Peach Canker.
The following recommendations are
taken from Bulletin No. 37, of the
Central Experimental Farm, which will
be sent on request to anyone inter-
ested:
"Keep the trees free from   all dead
and dying wood, because, this harbors
the canker fungus. Prune out all dead
twigs, especially on the main linbs so
that they cannot serve as starting
points for the canker. Make all prun-
ing wounds clean cut and cut as close
to the remaining limlb as possible. If
a projecting stub is left, part of it will
die and the dead tissue thus left serves
as a starting point for canker.
It is estimated that Brown Rot in
peaches causes a loss of at least 10 per
cent. of the crop annually, while peach
canker destroys each year from 3 to 5
per cent. of our bearing trees. These
figures will indicate the importance of
taking every method that will tend to
keep these diseases in check.
Will Use Nitrate of Soda
John Buchanan, Berwick, N.S.
This year I purpose using one-half
pound of nitrate of soda per tree in my
apple orchard for trees six years old
and under. Will use two pounds of
nitrate on thirty and forty year-old
trees. This will be put on as soon as
the frost is out of the ground-follow-
ing the results of the Oregon and Ohio
experimental stations.
I will throw the nitrate under the
spread of the branches and not broad-
cast over all the orchard. Mineral fer-
tilizers have shown no returns in in-
crease of apple crop with me, so I will
only buy enough to continue my trials.

March, 1919.