PAPAVER
somniferum.
CULTIVATION
Diseases.
Fungoid:
Peronospora.
54
Extracted from the Dictionary of
Diseases of the Poppy Plant.
more than the poppy. They grow up from the roots of the crop sending,
above ground a tuft of beautiful spikes of bluish flowers. When very pre
-valent they do considerable injury to the crop, but as they are large and
easily seen can be exterminated. Indeed, unless when very prevalent, they
rarely do any appreciable injury.
(g) Peronospora.–– The fungoid pests are far more destructive. Mr.
Scott devotes, however, so many pages to this subject that it is impossible
to produce a brief abstract of his views. The chief disease is Peronospora
arborescens – the poppy-mould. This appeared the first year (1872-73), as
seen by Mr. Scott, to so slight an extent that he was disposed to view it of
as of no great moment. In the following season it was manifested to an
almost alarming extent. But Mr. Scott may be allowed to describe this
disease in his own words. Speaking of the disease as seen in 1873-74 he
says :—" This was quite a periodic phenomenon, and extended from about
the middle of December to the middle of February. At the latter period
fully more than half the leaf surface of every plant was invaded and dis
-coloured by the mould. The invaded portions of the leaf are readily dis--
tinguished by their dry, escharotic appearance, and dull-brownish colour.
On examining the lower surface of these in February 1874, I found every
patch crowded with spore-bearing filaments. The mould had apparently
exhausted itself in this high reproductive fertility : it made no further exten--
sion, and the invaded parts dried up and withered, without causing rot or
further injury to the uninvaded parts of the leaf. From the result of that
season's observations of the mould, I had concluded that it was not at all
likely to prove a serious enemy to the poppy. The less succulent structure,
as compared with that of the potato, as I then wrote, is evidently
unfavourable to any rapid or general extension of the mycelial processes,
and out of the many thousands of poppy plants which I have now seen,
with their whole leaf surface teeming more or less with the fertile shoots of
the mould, I have not seen a single plant succumb to it : all have flowered,
yielded drug,—I am indeed not prepared to say in undiminished quantity,
and borne their normal quantity of good seeds.' Well-founded, apparently,
though the above view was, the following season's observations proved it
to be anything but true ; and the escape of the crops from a virulent
blight, proved simply to be due to the mode of development, as I will now
attempt to show in the following resumé, of the mould's extension and
morbific action on the poppy crops in the season 1874-75.
" The first appearance of the mould on the poppy in the experimental
gardens for the above season was towards the close of November 1874,
and, as in the previous season, I found it entirely confined to the lower
and mature leaves. It had again a periodic extension from the lower to
the upper cycle of leaves, and by the middle of February the whole leaf
series presented patches and streaks of a dark-brown colour, indicative of
mould invasion. Hitherto it had given me no anxiety, my observations on
extensively-affected specimens in the preceding season having afforded me
grounds for the belief that the drug-yielding qualities of the poppy would
not be sensibly impaired by the infection, nor did it appear in any marked
way to have weakened the plants, as even those with the older leaves very
extensively affected (the mycelium, as I should here observe, being fertile
or spore-bearing) continued in good health. . . . Each mould-patch
fructified copiously, and thus, as it would appear, utterly exhausted the
mycelium or spawn in the inner tissues; so that the latter and its fostering
matrix simply dried up, without communicating disease or rot to any un
-invaded portion of the leaf tissues. On the other hand, in the season
1874-75, the inner tissues of the leaves appear to have been wholly inter-