COTTON-PLANT DISEASES AND PESTS.
There are several classes of agents all of which act injuriously more or
less on the Cotton plant.
1. Climatic changes, including hygrometric variations of the
atmosphere, and extremes of heat and cold.
2. Insect pests.
3. Physiological diseases of the plant.
4. Blights caused by fungi.
It has been pointed out in the early pages of this story, how very
sensible to changes of heat and cold, the Cotton plant is, especially in
the early growing period. When the plant has just risen above the
ground, and is beginning to spread its roots, too great an amount of
heat would be fatal to its further growth.
Instances could be given where very serious decreases in the production
of cotton in the States especially have taken place, due entirely to
unusually high temperatures which obtained during the early growing
period of the Cotton plant.
Extremes of frost are likewise fatal to the growth of the young plant.
By the beginning of April, frosts have as a rule disappeared, and no
further fear need be felt on that account, though if the end of winter
has been abnormally warm, and the young plants have been making leaf too
quickly, it will be readily seen how fatal a sharp frost or two must be
to the young and tender plant. There are cases, however, when a frost
is beneficial.
Then again, while rain is needed in fair quantity, too much of it is
followed by rot and myriads of pests. If the planter desires anything at
all when his crop is ripe, it is fine weather in which to gather his
harvest.
Frequently large quantities of cotton are left on the plantations,
because it is too wet to gather it. This happened a few years ago to an
unusual extent, when a vast quantity of cotton had to be left upon the
fields.
Of all the injurious agents most dreaded in the cotton-growing districts
of the globe, none are so widely spread or so disastrous as "insect
pests."
They attack different parts of the plant during its growth, and when the
bolls are formed they commit great havoc among these by boring through
and completely ruining the immature fibre. Then again, while the plant
is young, they may attack the most tender portion of the plant, viz.,
the new and young leaves found at or near the top. This they soon clear
and make their way as caterpillars down the plant, and they frequently
clear it as though the leaves had been plucked off.
So completely do they do their work that it has been calculated in
certain years the loss on this account alone cannot have been far short
in America of 3-1/2 million pounds in one year.
Of the chief forms of insect pests, two specially stand out into
prominence, both of which belong to the moth tribe of insects, viz.,
_Alethia argillacea_ or Cotton Caterpillar, and the _Heliothis armiger_
or Cotton Boll-Caterpillar.
The operations of the former are mostly confined to devastating the
leaves and buds, while the latter confines its special attention to the
bolls which, were they allowed to ripen, would burst with cotton.
The eggs of the former, too, are laid on the under side of the upper
leaves and vast numbers are deposited. The moth flies by night, and the
eggs laid are extremely difficult to discover--indeed it takes an expert
to quickly find them.
Usually, about midsummer, the eggs are hatched in three or four days and
then comes the period for spoliation.
All that is tender is assimilated, usually the under side of the young
tender leaves found at the top of the plant.
During this stage of its existence the caterpillar moults five times and
the larva period varies somewhat according to the weather from one to
three weeks.
The chrysalis or pupa state covers from one week to four, and at last
emerges as a beautiful olive gray moth with a purplish lustre.
In about four days the female commences to lay eggs very rapidly and
will lay sometimes as many as six hundred during its life. No wonder,
then, with several generations during a season and vast numbers of
moths, that untold damages can be wrought by these particular insects in
a single season.
A number of remedies has been successfully applied in the direction of
spraying various chemical solutions, and in sowing plants which have had
the direct effect of reducing the spread of this terrible pest. Its
method of working can be seen on referring to Fig. 4.
Now the Boll-Caterpillar, though it lives much in the same way as the
Alethia, has a very different method of procedure so far as its
destructive habits are concerned.
And its fields and pastures, too, are by no means confined to one
continent, or to one kind of plant, for it attacks both the tomato and
corn plants. According to Dr. Howard, "It feeds upon peas, beans,
tobacco, pumpkin, squash, okra, and a number of garden flowering plants,
such as cultivated geranium, gladiolus, mignonette, as well as a number
of wild plants." As the name indicates, the Boll-Caterpillar makes the
boll its happy hunting-ground. The eggs are laid in the same way by the
parent moth as the Cotton Caterpillar or Alethia, and when hatched the
young powerfully jawed caterpillar makes its way to the newly-formed
boll, and applying itself vigorously, very soon gains an entrance. Here
it rests for a time, eating away at the best it can find. It ultimately
emerges and is transformed into the pupa, taking up its quarters in the
ground, until the next change takes place, when in a week or two's time
it appears as a moth much the same in size as its cousin the Alethia,
but coloured ochre yellow to dull olive-green and being more varied in
its markings. It will lay during one season about 500 eggs.
Many remedies have been applied for the extirpation of this particular
insect, but these only seem to have met with partial success. It will
readily be seen how much more difficult this pest is to deal with than
the preceding one. Living as it does in the boll and in the ground for a
great part of its existence, it will be exceedingly difficult to get
at.
In Mexico what is known as the Cotton-Boll Weevil (_Anthonomus grundis_)
appears to do great mischief to the Cotton plant. It does most damage
during the larvae stage, eating up the tender portions of the boll while
in residence here. When matured it is only a little under half an inch
in length.
Many other insects act injuriously upon the Cotton plant, but the
following may be taken as the chief: Cotton Cutworm (_Feltia malefida_);
Cotton lice (_Aphis gossypii_). Among the lepidoptera may be mentioned,
_Cocaecia rosaceana_, or "Leaf-roller," so called from its habit of
curiously rolling the leaves of the Cotton plant and then feeding inside
the roll. Then grasshoppers and locusts occasionally do some damage, as
well as a beetle named _Ataxia crypta_, which is noted for attacking the
stalks of the Cotton plants, but it should be pointed out this beetle
does not prey upon healthy and vigorous plants at all.
Scores of other insects could be mentioned as injurious, though some of
them do but very slight damage indeed to the Cotton plant.
It does appear, however, from long years of experiment and observations,
that little damage needs to be feared if the plants, while growing, and
during the formation of the boll, can be carefully watched and guarded.
The plants when matured are better able to withstand the onslaughts
which these predaceous insects make upon them.
Then again, there are large numbers of physiological diseases of the
cotton due to inherent weakness of the plant or failure of assimilative
processes.
And lastly, vast numbers of fungi, too numerous to mention here, work
serious injury to leaf, flower and boll in certain seasons of the year.