The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
AGRICULTURAL RESEARCH EDUCATION CENTER
GCS Mimeo Report GCS71-8 December, 1971
CHEMICAL TREATMENT OF GLADIOLUS CORMS AND HOT-WATER TREATMENT
OF CORMELS AND SMALL CORMS
R. 0. Magie
The mercury chemicals relied on for 35 years in the preplant treatment of
gladiolus corms were taken off the market in recent years. Among the highly
effective non-mercuric fungicides labeled for gladiolus corm treatment and still
available are Busan 72, Benlate and Mertect 160. Fortunately, these were de-
veloped and marketed before the last of the mercury fungicides were discontinued.
Another very effective chemical used by growers for prestorage and pre-
plant treatments is Dowicide B. Other fungicides which are still available but
less effective against Fusarium disease are captain, Phaltan and Arasan or
All of these chemicals may be used to treat corms after harvest or be-
fore storage as well as before planting. The after-cleaning treatment is
standard for commercial flower growers who clean jumbo corms at harvest. Two
dip treatments, one after cleaning and one before planting, may be used on
varieties or stocks with a history of corm rotting. Also, corms dusted after
cleaning may be dipped before planting. In tests of double treatments, the
results show that the fungicide used for the preplant treatment should be dif-
ferent than that used after cleaning. Benlate or Mertect 160, for instance,
might be used as a dust or dip at cleaning time followed by a Busan 72 dip
before planting. The efficacy of Benlate and especially of Mertect is greatly
improved in disease control by raising the temperature for the 15 minute dip
to 1200F (490C).
Many of the fungus infections that result in rotting of corms in storage
take place through wounds at digging time. To prevent these infections, it is
very important to use a fungicide the same day that corms are dug, immediately
if possible. Either a dip or dust treatment is effective if applied immediately
after the wounding. Quick drying of corms does not prevent all of these in-
Large flower growers clean jumbo corms at harvest and dip or dust them
immediately. However, if corms are to be cured before cleaning, they should be
washed with running water as they are harvested, drained, and dipped for 15
minutes in one of the recommended fungicides mentioned above. After the corms
are cured and cleaned they may be dusted with Benlate or Mertect 160 which may
be used full strength, or diluted with a non-toxic dust to a concentration of
In treating corms, there has been no trouble with incompatibilities be-
tween any two of the recommended fungicides when mixed or used in succession.
Also Botran is compatible with those fungicides and may be added to the dip
or dust, or applied in the furrow at planting.
Where thrips are a problem, USDA workers suggest that corms to be stored
may be dusted with any one of the following insecticides: 1% lindane, 4% mala-
thion, 5% carbaryl, 5% diazanon. These percentages refer to active ingredient
only. Also a 1 to 2 gram strip of dichlorvos (VaponaR) killed thrips in a
closed bag of 100 corms in the USDA tests. Aphids are more difficult to con-
trol than thrips on corms. Lindane as a 5% dust or a wettable formulation or
liquid added to the fungicidal dip might be tried where aphids are a problem.
Growers of corms are finding that the least expensive and most effective
way to control corm diseases is to use the hot-water treatment. In fact, with-
out proper use of this treatment, it is becoming difficult if not impossible
to adequately control Fusarium rot disease in larger operations. With the new
systemic fungicides, Mertect 160 and Benlate, we can now greatly improve the
hot-water treatment, making it more effective and practical for large and small
growers to use in all growing areas.
Small corms as well as cormels should be treated in hot water. In the
past, hot water has often killed them so caution must be exercised. Unless corms
and cormels are sufficiently dormant, they may not tolerate the higher tempera-
tures used to eliminate the fungi carried in and on corms.
During the past 3 seasons our experiments have shown that the addition
of Mertect or Benlate to the hot water allows a lower temperature to be used
effectively and also tends to protect corms or cormels from injury at temperatures
that kill them in water alone. These systemic chemicals therefore improve the
hot water treatment in two ways.
Last year Mr. Alex Summerville of New Jersey supplied a bushel each of
'Angel Eyes' and '7-59V' for our experiments on corms and cormels with less
dormancy or heat tolerance than those grown in Florida. The small corms and
cormels were grown in New Jersey from cormels that had been treated early in
February 1970 in hot water at 1300F. The corms were dug between October 10-20
and held at room temperature until December 1, then held at 48-550F in New Jersey
until treated with hot water plus chemicals in Florida on February 18, 1971.
Half were planted on February 25 and half on September 8, 1971. Having been
stored at low temperatures, these northern-grown corms were mostly killed by
the higher temperatures (133-1370F) usually used to kill Fusarium fungus. Cor-
mels too were damaged by the higher temperatures. The addition of one ounce of
Mertect 160 or Benlate 50W per 10 gallons of heated water reduced the damage
and increased production of corms and cormels. When 1 1/2 tablespoons of
Ethrel were added also, the production of corms and cormels was increased again
by as much as 100%. Ethrel also improved corm yields vhen added to water alone
The results of these and other tests during the past 3 years can be sum-
marized as follows: After harvest, hold corms and cormels at about 68 to 780F
for 7 to 11 weeks in order to develop a dormant condition. Just before the
hot-water treatment, soak both corms and small cormels in running water for 1
or 2 days. Put the corms or cormels into boxes or bags made of plastic or
wire screening material because cloth bags remove too much of the fungicide
powder from the hot water. Plastic mesh sacks are quite suitable. Leave a
third of the sack empty for cormels to float and to allow circulation of water.
Use a large volume of hot water so that the temperature is not appreciably
lowered when the cold material is added. It is very important to circulate the
hot water strongly through the corms and cormels for the full 30 minutes of
the treatment. Add 1 to 1 1/2 ounces of Benlate or Mertect 160 per 10 gallons
of the hot water. Replenish the fungicide as it is removed by the cormels,
containers, etc. and make up a fresh mixture after each half day's use. After
30 minutes immersion at the desired temperature, place corms and cormels in
shallow layers to cool and dry. Do not cool in water, which would remove the
fungicide. When surface-dried, place in cool storage.
Where cormels are hot-water treated in cloth sacks the problem of fungicide
removal and lowering of fungicidal concentration by sacks and cormels may be
solved by dissolving Mertect with alum. For each pound of the 60W powder add 6
pounds of ammonium alum and stir for about 30 minutes. The inert 40% of the
powder does not dissolve. Mertect solutions have been more effective and as
safe as suspensions of the wettable powder in cool and in hot water treatments
for corms and cormels. Benlate has not been dissolved.
Treatment temperatures suggested: For small corms harvested in warm wea-
ther, use a water temperature of 133-134F (56.5C) and for the cormels, use
135-136F (57.5C). For small corms dug in cool soils use 129-1300F (54.30C) and
for cormels use 131-132F (55.30C). Treat the larger, partly naked cormels the
same as for corms because cormels with cracked husks do not tolerate the high
temperatures as do cormels with intact husks.
Several tests show that Benlate produces more healthy corms and cormels than
Mertect at 1330F, but that Mertect is better than Benlate at 136.
After cormels and corms have been in cool storage (36-450F) for at least
4 weeks and about 2 weeks before time to plant, remove to a warm room if root
swellings have not developed. This development is accelerated as the temperature
of the room is raised. The air should be circulated through the containers of
corms and cormels and the temperature should not go over 860F. They should be
planted when root "buds" are well developed and before soft roots begin to grow.
Cormels should be soaked in water to soften husks just before planting. To re-
place the fungicide removed by the water, dip them in Benlate or Mertect as
suggested in the labels.