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Copyright 2005, Board of Trustees, University
GULL COAST STATION J;Ii O REPORT 54-8
GLADIOLUS STROMATINIA DISEASE MAY 20 1954
R. 0. Magie
The gladiolus disease commonly called dry rot in other areas has been called
Sclerotinia neck rot in Florida because dry rotting of corms is not known to occur
in peninsular Florida. The fungus which causes this neck rot and dry rot was re-
cently found to belong to a closely related genus and is now named Stromatinia
gladioli (Drayton) Whet. This fungus was not known to cause a serious disease of
the roots until 1953-54 when losses were heavy in some Gulf Coast farms. The loss
in the Tampa Bay area alone is estimated to be over'$100,000.
Dry rot of corms and neck rot caused by Stromatinia is a major disease of
gladiolus in Western Washington, parts of Michigan and some other regions where
growing-season temperatures are relatively low and rainfall is plentiful. In Florida
the neck rot has been most severe when unusually cool weather occurs in October or
the first two weeks in November,
Moisture is an important factor in disease development. Root infection was
most severe in the lower and wetter parts of fields. Neck rot has been most prev-
alent in seasons of abundant rainfall. poot rot was found to be severe in some
fields where neck rot was scarce or absent.
DI SE S nYPTQOS
Stromatinia neck rot may appear similar to Fusarium yellows and the root rot
looks like other root rot troubles. However, the disease may be positively identi-
fied by the small, round, black sclerotia which are imbedded in the dead tissues.
These sclerotia can lie dormant in the soil for one or more years. Some of them
stay alive for many years. A magnifying glass should be used to find these shiny,
black, pimple-like bodies on the roots.
It is often difficult to find gclerotia on the roots because sclerotia are not
formed until the tissue has been dead for several days or weeks and because the outer
part of the root usually sloughs off, leaving the sclerotia in the soil. Sclerotia
are found only in the cortex or bark of the root, They are seen more readily when
the roots are washed and dried.
Infected roots turn yellow and brown. After the softer, outer part sloughs
off, the central, woody part of the root is often found to be white and tough with
a wiry, rough texture when dry.
In the neck rot phase of the disease the outer leaves are killed first. The
sclerotia usually are not formed until the whole neck is rotted. The rotted neck
tissues become very dark brown and shredded. The dead stalk may be pulled away
from the corm easily. In contrast to plants killed by Fusarium, the corm is found
to be sound but stunted.
Corms are usually attacked by way of the husks or leaf bases. Shallow black
lesions develop along the lines of husk attachment. Occasionally the disease fol-
lows the vascular tubes into the core. The infected vascular tissue is greenish
black or dark brown.
CARRIED ON CORIS
Corms which appear to be free of any infections may carry the fungus to the
soil. The fungus spreads from corm to corm and root to root. If the weather is
relatively dry and warm, there is little or no above-ground evidence of disease
but enough sclerotia may be produced on roots to initiate serious disease develop-
ment in future plantings on the infested land. Severe loss from Stromatinia was
experienced in a field planted with seedling corms. The infection came from the
soil, not from the corms, because they were grown from seed in a seedbed of methyl
bromide-treated soil. This field had been planted to gladiolus only once before
with untreated corms from an out-of-state source. Enough sclerotia to initiate
this severe epidemic were produced, probably on the roots, without any obvious, a-
bove-ground disease symptoms in the January planting of corms that preceded the epi-
The disease originates both from corms that carry the fungus and from sclero-
tia in the soil. When it originated from corms, neck rot appeared as early as Octo-
ber 1 in a September 8 planting on new land. When the disease originated only from
sclerotia carried in the soil, however, neck rot did not develop until November or
December, indicating that periods of cool weather are required to activate the dor-
Rotation of fields. -- In gladiolus areas on the Gulf Coast, new fields
should not be planted in consecutive years unless the corms are grown from corm-
lets and planting stocks produced on clean land. Fields which showed neck rot
or root rot should not be planted to gladiolus for at least two years. During
the years when gladiolus are not grown in a field, care must be taken to keep down
the growth of volunteer gladiolus by disking, at least during October, November,
December and January when sclerotia would be produced abundantly. This also ap"-
plies to fields in which late winter plantings are to be made. The infection could
spread from the volunteers to the new planting, even though the volunteers were
Time of planting. -- As mentioned above when clean corms were planted in
contaminated or diseased soil, neck rot symptoms did not appear in plantings made
before September 15 or after January 15. Cool temperatures which normally occur
in November apparently are required to activate many of the sclerotia remaining in
the soil. Field evidence also indicates that those sclerotia which are susceptible
to stimulation by cool weather have mostly germinated before January and are no
longer able to attack gladiolus. November and December plantings were most severe-
ly attacked, presumably because the plants became diseased during the early stages
of growth. When plants were not attacked until they were mature, disease development
was sparse but sclerotia were produced in numbers sufficient to initiate severe epi-
demics in future years.
Sanitation. -- Whenever possible, clean land should not be contaminated by
planting diseased corms, or corms that grew on contaminated land, if gladiolus are
to be grown in those fields in subsequent years. Such corms may be planted on con-
taminated or questionable land in August or after January 15 because the disease is
less severe in very early or in very late plantings.
Contamination of soil by sclerotia may be reduced somewhat by pulling out
plants at the first sign of neck rot, by harvesting early and by raking the tops
off the field immediately after corm harvest.
Drier soil, high beds and lower water table would probably help in control-
ling the disease because the fungus is reported to grow through wet soil more rapid-
ly than through drier soil. Corms planted during October through December may be
covered with as little as an inch of soil until the third week. This would reduce
neck rot infection. The planting furrows should be filled and the beds built up
gradually over a period of four weeks.
Corm treatment is very helpful in controlling Stromatinia disease, especially
when plantings are made in uncontaminated or relatively "clean" soil. Corm treat-
ment will not prevent all disease development and sclerotia formation. Dr. C. J.
Gould in western Washington found that the N. I. Ceresan dip is one of the most ef-
fective preplanting treatments. However, because Ceresan reduces flower yield in
that area, he recommends Tersan for treating corms in dry rot control.
Corms of all varieties and of all sizes should be treated. Since control of
Fusarium disease is of prime importance in Florida, the following treatments are
suggested for both diseases.
A. For Picardy corms and other varieties that are fairly tolerant of N. I. Ceresan
1. After cleaning corms wait 4 to 18 hours and then soak them 15 minutes in solu-
tion of 2 pounds Dowicide B in 50 gallons water plus 1/2 cup of detergent such
as Glim or Joy. Before planting these corms, soak them for one minute in 1
pound of N. I. Ceresan wetted with detergent and mixed in 50 gallons of water.
The one-minute treatment has resulted in better flower production and nearly
as good disease control as the ten-minute treatment.
2. Soak conms for 10 minutes just before planting in 1 pound N. I. Ceresan wetted
with detergent and mixed in 50 gallons of water.
B. For Valeria corms and possibly other varieties that are injured by the regular 10
or 15-minute N. I. Ceresan treatment.
1. Same as No. 1 above
2. Soak corms 15 minutes in mixture of 5 pounds thiram 75 percent wettable (Tersan
75) in 50 gallons water. Stir before' each batch of corms and agitate corms in
the dip. This chemical is expensive but the dip can be re-used indefinitely if
more of the fresh dip is added to maintain volume.
C. No treatment is recommended for cormlets. Tests are being made to find an effec-
tive but safe treatment.
Soil treatment, using 1500 lb. calcium cyanamid per acre, was fairly effec-
tive in one test. A period of at least 60 days must elapse between the broadcast
application and the planting of gladiolus. Wait another month if the soil is not
continuously moist following treatment. A waiting period of 90 days is suggested
for winter and spring applications because gladiolus are very sensitive to the break-
down products of cyanamid.
Flooding may prove to be very helpful in controlling the gladiolus Stroma-
tinia disease because it is effective against sclerotia of similar fungi. Flooding
of soil for three weeks during summer or early fall is effective in killing the glad-
iolus Fusarium. If the water can be held high e;icuh to cover the surface for at
least three weeks, gladiolus fields which have been cropped several times would be
This disease is much more damaging and widespread than previously recognized
and will probably tend to become more severe as fields and corm stocks become more
generally infested. It appears that some cases of gladiolus root rot which were
blamed on nematodes were probably caused by Stromatinia. The fact that the fungus
becomes established in the soil so quickly and spreads from plant to plant so read-
ily makes this a major disease. The most important considerations in avoiding heavy
losses from Stromatinia are 1) Rotate fields, planting gladiolus once in three years;
2) Avoid planting corms from "diseased" land in "new" land; 3) Plant infested corms
or infested fields very early or very late in planting season; 4) Treat corms and 5)
Use the minimum irrigation riter necessary to produce quality spikes.