Journal of Agricultural Research 
Vol. XXIX, No. 4 
160 
darker in color. (Sanford's brown to 
hazel brown for lightest color and ma¬ 
hogany brown to black for the dark¬ 
est (7). 3 These spots look quite like 
burned places, the margins especially 
resembling charcoal. The fibrovascu- 
lar bundles are not primarily attacked 
and stand out prominently in the 
sunken areas. Ordinarily the infected 
tissues are rather dry and firm, but if 
the plants are kept under unusually 
moist conditions the disease progresses 
rapidly like a general soft rot and 
without the brightly colored, definitely 
outlined spots. 
Infection is most general on the 
lower parts of the leaves, from ground 
level up to a height of 6 to 8 inches. 
Under favorable conditions the spots 
enlarge rather rapidly and soon destroy 
large areas of the soft tissues. The 
whole thickness of the leaf is involved, 
and protected from drying influences by 
the outer leaves, the rot progresses 
more rapidly in the interior and has 
here more of the appearance of a soft 
rot. Plants showing but slight exterior 
signs of disease often show a surprising 
amount of rot when the leaves are 
pulled apart. The underground stem¬ 
like part just above the corm usually 
shows evidence of the disease, either as 
tiny reddish-brown spots or as a more 
extensive rot. 
So long as the fibrovascular system 
functions the leaf parts above the 
lesions remain normal. The vascular 
system seems not to be directly af¬ 
fected, but eventually the vessels be¬ 
come blocked with a brownish, gum¬ 
like substance and the leaf parts above 
die. Sometimes only a narrow, dry, 
brown streak is present in a leaf; more 
often the whole leaf is brown arid dry. 
In some cases one or more brown leaves 
are seen in plants otherwise normal in 
appearance (PI. 2). 
In cases of severe infection, with 
destruction of large areas of cellular tis¬ 
sue, the whole plant falls over, bending 
at or near the ground level. At this 
stage of the disease the basal parts are 
dull brown in color, fibrous, and soft- 
rotted or drv-rotted, depending on the 
amount of moisture present (PI. 1, A). 
The upper parts of the leaves have 
but few infections. These remain small 
and cause no damage except to the 
appearance of the foliage (PI. 4, F). 
The date of the appearance of the 
disease depends largely on the tem¬ 
perature and moisture conditions. 
Warm, moist weather seems a neces¬ 
sary factor for infection. In the 
vicinity of Washington, D. C., the 
earliest noted appearance was June 6 r 
1921, on the variety America. The 
plants, about 1,300 in number, were 
from corms that had remained in the 
ground all winter. In 1920 the plants- 
in this bed were moderately infected 
with the disease. The 1921 shoots 
came up early in April and remained 
entirely normal, clean, and vigorous 
until June 6, when the first small but 
typical spots were found. Isolation 
plates from these spots produced the 
characteristic bacterial colonies. On 
June 8, about 20 per cent of the 
plants in this bed showed lesions on 
the lower leaves. After June 6, the 
disease gradually increased in number 
of plants infected and severity of 
attack. Many outer leaves and a few 
whole plants rotted off near the ground 
level. Plants with average or slight, 
infection produced fine flower spikes. 
It was observed that occasionally of 
two plants springing from the same 
corm one would be infected, the other 
entirely free from infection. An ad¬ 
joining bed of about 1,000 plants from 
newly purchased corms (varieties Au¬ 
gusta and Mrs. Francis King), growing 
on soil not recently, if ever, planted to 
gladioli, had on June 8, no indication 
of disease. Later in the season a few 
definite cases of the disease were found 
in this bed. 
In the fall of 1921 the corms from 
both beds were dug and placed in 
storage. In the spring of 1922 they 
were planted in the plats used the two 
previous seasons. The early growth 
was normal but as the season advanced 
the disease appeared and increased in 
severity until by September practically 
all the plants were more or less affected. 
Out of about 1,400 (all that survived of 
the two lots) only. 13 showed no out¬ 
ward sign of the disease. In 1923 the 
disease was again prevalent in the same 
plats of ground, planted with old and 
some new stock, but owing to cool 
weather in the early part of the season 
the disease was not evident until early 
July. 
In an examination of a large planting 
in Michigan, where this disease had 
caused more or less trouble for the past 
10 years, it was noted that the leaves of 
young stock were usually entirely free 
from the disease and that the older 
plants were affected in proportion to 
their age. This seems to indicate that a 
diseased plant carries the disease along 
from year to year, the disease increas¬ 
ing in severity until the plant suc¬ 
cumbs. The grower stated that he 
believed this disease to be the eventual 
3 Reference is made by number (italic) to Literature cited, p. 117. 
