EPIPHYTICAL PARASITES (VEGETABLE BLIGHTS) OF CORN CROPS.
These forms of parasite are so numerous, that nearly every species of
flowering plant may become the nidus even of several named genera, with
many species, or, at least, varieties of them. We here say attacked,
because the advent of many of their forms passes under the name of
“blight;” a term which at once recognises their injurious tendency.
Whether these epiphytes are the causes of the so-called blighted
conditions, or merely their effects, is a subject upon which no little
discussion has been expended. We do not, however, mean to re-open the
question here; we will only remark, that in all probability this very
wide range of the lower tribes of the vegetable kingdom is very variable
in these respects.
Again: it will be impossible to enter into details of the different
species of epiphytes. We shall hope, therefore, to elucidate their
natural history, in so far as the farmer is concerned, by pointing out
the more general facts connected with the following forms:—
1. _Uredo segetum_—Smut or dust-brand of wheat, barley, and grasses.
2. _Uredo caries_ (_Tilletia_)—Bunt }
}
3. _Uredo rubigo_—Red gum or red robin }
} of wheat.
4. _Uredo linearis_ } }
}—Straw-rust, or “mildew” }
5. _Puccinia graminis_ } }
6. _Puccinia fabæ_—Bean-rust.
7. _Æcidium berberidis_—Barberry-rust.
8. _Cladosporium herbarum_—Corn-ear mould.
9. _Botrytis infestans_—Potato-mould and mildew.
10. _Botrytis_—Turnip-mildew.
11. _Oïdium erysiphioides_ }
} Hop-mildew.
12. _Erysiphe macularis_ }
13. _Oïdium abortifaciens_—Ergot of grasses.
1. _Uredo segetum_, Smut or Dust-brand, is common to barley, and not
unfrequent in wheat; in both of which crops it is easily recognised from
the affected ears of corn appearing as though they had been powdered
over from the sweep’s soot-bag. On closely examining these blackened
ears, we find that the whole flower has, as it were, effloresced into a
black powder, which, on being placed under the microscope, is shown to
be composed of myriads of granules, called by the fungologist _spores_,
in which latter are contained still smaller grains, or _sporidia_.
These black spores are all washed away by the time the crop is ripe,
leaving the stalks bare and grainless, so that the sample suffers no
injury from this blight, which, even if present after threshing, would
only tend to a slight discoloration of the sample, which is remediable
by the smutter. Its chief effect, however, consists in causing the loss
of much grain. We have observed it to the extent of as much as an
eighth, but usually the diminution is about equal to the amount of seed
sown; though it is not improbable that the whole crop may in many cases
be greater when the smut is present. Sheep-folding previous to barley,
special manuring for this crop, and other causes of increased fertility,
are constant causes of the increase of the dust-brand.
2. _Uredo caries_—Bunt, Pepper-brand, Smut-balls.—This blight differs
from the preceding in the fact that in the grain no flower is formed,
but its interior becomes filled with a dark powder, which, when viewed
under a high magnifying power, is found to consist of granules, with a
surface which is rough, and not smooth as in the dust-brand.
In most cases, the whole grains of the ear will be so affected; in
others, only a portion of them. They will be gathered in the harvest,
and as the diseased grain is readily crushed, the black powder
materially damages the appearance of the sample. Nor is this all: this
blight has a most disagreeable odour and flavour, both of which are
communicated to the sample, and so, besides diminishing the amount of
produce, it greatly deteriorates it. Its specific name of _caries_ of
course refers to this fact, as also does that of _U. fœtida_, adopted by
Baur, an author to whom we are greatly indebted for information upon
these curious productions.
Before considering the remedy for this evil, it will be well to
distinguish it from the “purples, ear-cockle, or peppercorn” (_vibrio
tritici_)—a name expressive of its animal origin, and frequently
rendered “wheat-eels.” In the purples, the grain is shorter than a
healthy wheat grain, irregular in shape (cockled), and purple
externally; but its interior is filled with what, to the naked eye, is
like very short white cotton-wool. On placing a bit of this woolly
substance with the point of a needle on a slip of glass, just touching
it with water and submitting it to a high magnifying power, the term
“wheat-eel” will at once be seen to be justified; for, if alive,
thousands of eel-like creatures will be seen writhing in the fluid.
The differences of these two affections of wheat may be expressed as
follows:—
_Bunt._ _Ear-cockle._
Grain smooth externally, sometimes Grain cockled and irregular in
appearing black from blackened shape, purple externally, skin
interior grains showing through thickened, interior of the grains
the thin epidermis (bran). These stuffed with a white cottony
corns easily crush beneath the substance, not compressible by
finger, emitting the black fungi. the finger; but being opened, and
the interior magnified, exhibits
the living wheat-eels.
As regards the ear-cockle, we incline to the belief that a damp
atmosphere and cold soil are chiefly concerned in its spread, if not in
its production. As we have shown the difference between it and bunt, we
now proceed to offer a few remarks upon the production of the latter,
and its remedies.
Bunt is mainly produced by defective seed. It occurs on all kinds of
soils—sands, clays, and limestones—and is not peculiar to any climate.
Professor Henslow believes the disease to be wholly propagated by the
spores of the fungus adhering to the wheat-seed. He says, “It has been
clearly proved that wheat plants may be easily infected, and the disease
thus propagated, by simply rubbing the seeds before they are sown with
the black powder or spores of the fungus. It is also clearly ascertained
that if seeds thus tainted be thoroughly cleansed, the plants raised
from them will not be infected;” and he deduces from this a proof in
favour of steeping; for he says, “This fact is now so well established,
that the practice of washing or steeping seed wheat in certain
solutions almost universally prevails.”[17]
[17] See an essay on _Diseases of Wheat_, in the _Journal of the Royal
Agricultural Society_ for 1841, by the Rev. Professor Henslow.
Our own experiments, however, recorded in the “Journal of the Royal
Agricultural Society” for 1856, led us to conclude that the success
derived from pickling wheat in different caustic and corrosive solutions
arose from the fact of diseased grain being destroyed in the process;
and we extract the following record of experiments made in 1853, as
explaining this view of the matter.
Four plots of wheat, all from the same sample, were sown in the
following order:—
1. 2. 3. 4.
+---------------++---------------++---------------++---------------+
| Much diseased || Much diseased;||Perfect picked || Perfect picked|
| wheat, || treated with || seed, || seed, with |
|without pickle.|| sulphate of ||without pickle.|| sulphate of |
| || copper. || || copper. |
+---------------++---------------++---------------++---------------+
The results of these were as under:—
Plot 1. Most of the seed germinated, but the crop was much blighted,
both in straw and grain; in fact, scarcely a perfect ear of the latter.
Plot 2. A small quantity of the seed germinated; the few resulting ears
were free from blight.
Plot 3. Germinated, with a good and clean resulting crop.
Plot 4. The same result as Plot 3.
These experiments seemed to show that the pickling of wheat destroys the
seed, so as to prevent germination when the seed is diseased or
ill-formed; but if perfect seed be always employed, no pickling at all
is necessary, it being strictly true that a diseased progeny must result
from an imperfect stock in plants no less than in animals.
We have said that bunt is not peculiar to any climate; we have, however,
always observed that employing seed from a warm district on a cold one,
or using the finer white wheats in cold, exposed, or ill-drained
situations, is sure to produce a large quantity of this fungus.
Autumn-sown wheat, too, is less liable to the infection than spring
wheat, which we attribute to the fact that many of the weaker plants
will succumb to the cold rain and frost.
3. _Uredo rubigo_ (Red-rust, Red-rag, Red-robin) makes its appearance in
the inside of the chaff-scales, and ultimately in the green epidermis of
the growing grains of wheat. Its first appearance is that of oval
pustules, caused by the raising of the skin, which, ultimately bursting,
shows the orange-coloured spores of the epiphyte. This must not be
confounded with _Cecidomyia tritici_ (wheat-midge), the larvæ of which
are of a bright orange-colour; in the latter, the living moving worms
may be easily detected by any common pocket lens or magnifying glass.
Both these pests, to which we would apply the distinctive terms of
_Uredo rubigo_ (red-rust) and _Cecidomyia tritici_ (red-gum), are
exceedingly common in some seasons, and not unfrequently in the same
crop. Good deep cultivation is the best remedy for the rust; but the
treatment of the fly is a different matter. We would suggest the burning
of smother-heaps on calm days, just as the wheat is bursting into ear,
as smoke is decidedly obnoxious to these small insects, which in some
seasons may be seen in thousands about the bursting wheat.
4 and 5. _Uredo linearis_; _Puccinia graminis_ (Straw-rust and
Mildew).—We refer to these epiphytes under one heading, as there can be
but little doubt that the latter is a more advanced state of the former.
They both occur in oblong patches on the leaves and straw of wheats and
other grasses: in the _uredo_ stage, of a dull red colour; in the
_puccinia_ stage, of a blackish hue. They are both, as, indeed, are all
these fungi, interesting microscopic objects; but our object now is to
describe them popularly. Both will always be found in abundance in cold
poor soils, and more especially if the finer wheats be grown in such
situations. The application of a dressing of salt to the soil is said to
be a preventive. Be this as it may, the disease is said to be rarer in
Cheshire, where salt is so much used by the farmer, than in any other
county, in as far as we have observed.
Here, again, we incline to think that these are morbid affections of the
plant. They are, indeed, viewed as such by Unger, in his “Die Exantheme
Pflanzen,” in which the very title classes them with eruptive diseases
of animals. Berkeley and Henslow, the two great authorities, however, do
not accord with this view: the former remarks in reference to it—“Surely
these plants are too distinctly, too regularly, and too beautifully
organized to be the products of disease like warts or purulent matter in
animals.” As, however, the microscope demonstrates that warts and
eruptive diseases have also their special and curiously formed
organisms, such a mode of reasoning is not conclusive.
Weeds have a great influence in producing mildew, which perhaps may be
accounted for from the fact that weeds are in active growth as the
wheat-stalks decline in vigour; and hence the constant evaporation of
moisture from the weeds to the wheat is continually re-moistening an
ever-drying surface—a most fertile source of mildew and moulds of
several descriptions.
6. _Puccinia fabæ_ (Bean-rust).[18]—The brown pustular rust-looking
spots on the foliage of beans, and, indeed, occasionally on the stems
and pods of beans, are sometimes common to this crop. They are usually
accompanied by a lessening both in quantity and quality of this pulse,
both in the garden and in field culture, but certainly more generally in
the latter. Too gross manuring without well mixing the dung with the
soil would seem to be a constant source of the evil. In fact, highly
nitrogenized manures appear to favour the development of all this class
of epiphytes, just as too much meat might bring about different forms of
rash or eruptions in the animal. Weeds, which are too much permitted in
beans, here aid in perfecting the mischief; hence, then, we may perhaps
take it for granted that the mention of the causes of mischief suggests
the remedy.
[18] This blight is mentioned here on account of its affinity to the
former.
7. _Æcidium berberidis_ (Barberry-rust) is here referred to, from the
opinion prevailing that it is the cause of rust and mildew in wheat. We
can no more believe that the barberry-rust would produce rust in wheat,
than the rust of any other plant would do so; for nearly all plants are
affected with some kind or other of rust. This epiphyte, too, is very
different in structure from wheat-rust. Still, that wheat growing under
a barberry hedge may be more blighted than in the rest of the field is
quite true; and so it is with wheat grown under any kind of hedge. High
fences are known to favour wheat blights; open, exposed, well-cultivated
positions, when not too elevated, and without trees or hedges, being
those in which the best wheats are grown.
8. _Cladosporium herbarum_ (Corn-ear Mould) is a brown-coloured mildew,
mostly occurring on the exterior of the chaff-scales of wheat, but
common to many plants in a state of decadence. It consists of greenish
or blackish tufts, which appear on the outside of the chaff-scales of
wheat under the two following conditions:—
On wet soils, where the ears appear to have been prematurely starved.
On dry sands, where long-continued drought has caused some ears to
wither and die before the seed was fully formed.
In both these cases we see that the plant has been previously injured.
The decay commences under alternations of moisture and drying, and hence
the fungoid attack. Here, then, the conditions necessary for preventing
will be deep cultivation and a due pulverization and mixture of the
soils.
9-12. _Botrytis_, _&c._ (Mildew).—Under this head we include a multitude
of epiphytes, to which the terms mildew, mealdew, mehlthau (Germ.) are
applicable. They appear to the naked eye as patches of white dust or
meal on the leaves and stems of the affected plants. With the microscope
we see that they are beautifully-organized plants, having a kind of
rootlet (mycelium) or spawn entering the tissues of the living plants on
which they grow, and delicate pedicels supporting spores at the
externally visible portion of the plant. The botrytis of the potato and
turnip, the erysiphe or oïdium of the hop, vine, and other plants, are
only different forms of mildew, which in some shape or another will be
found on most plants. That these attack living tissues is quite certain;
but in the case of the potato, the turnip, and the vine, there is reason
to believe that they result, to a very considerable extent, from
diseased action in their tissues. For example: the botrytis of the
potato seems to attack a crop much over-cultivated, on the approach of
wet and cold nights after a prosperous growth in warm sunshine. So, the
oïdium seems to us to be most abundant on renewed growth after a season
of dry weather. Again: mildew in turnips is sure to follow that check
which a long season of dry weather brings after a prosperous and
vigorous growth. All these circumstances at least show how these attacks
are favoured by the conditions which bring disease. So much, indeed, is
this the case, that we found, upon experimenting with some cucumbers in
a warm stove, that as long as we regularly watered the plants and gave
them the requisite air, they kept healthy; but, by neglecting these
conditions for a few days, we obtained mildew with the greatest
certainty.
The remedies against mildew are—to obtain as healthy a growth as
possible, and to maintain this with as great regularity as
circumstances will permit. Of late years, both the mildew of the vine
and the hop have been treated with flowers of sulphur. Dusting the
affected hop-leaves with sulphur certainly arrests the mildew in an
incredibly short time; and we found that by dusting sulphur from a fine
sieve on our cucumber plants, the disease was immediately arrested in
its progress. We therefore look upon this as an invaluable remedy in
these states of mildew, whether occurring on the vine, the hop, the
turnip, the cucumber, or on other plants, as we have frequently seen it
in hothouses—a circumstance which shows the near affinity of all those
forms of epiphytes, which, perhaps, after all, only vary with the
variations in the structure and economy of the different plants on which
they occur.
13. _Oïdium abortifaciens_ (Ergot); _Secale cornutum_ (Ergot of
Rye).—The black horn-looking spur which occurs in rye and other grasses
was formerly looked upon as a distinct fungus; now, however, it is known
to be a diseased or malformed condition of the grain or seed, resulting
from an attack by an oïdium on the immature seed.
Most of the cereal and even the meadow grasses are liable to attacks of
ergot, which is increased by cold damp fogs and a moist condition of the
atmosphere, the difference of the size of the spur being in accordance
with the size of the affected grass seed. Thus, in rye we have seen
spurs more than an inch long, while in the cock’s-foot grass it is
seldom a quarter of an inch.
The ergot, as it occurs in the rye, is much used by medical men in
difficult cases of parturition; and we have had evidence before us, in
some cases of abortion in cows, that the constant depasturing on grasses
affected with ergot (and the _Lolium perenne_ in aftermaths is often
especially so) has been the predisposing cause.