HISTORIC NOTE

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
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site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

GULF COAST STATION MIMEO REPORT 55-1
Bradenton, Florida

NOTES ON GLADIOLUS DISEASE RESEARCH 1954

R. 0. Magie

Controlling Leaf and Flower Diseases

Manzate and Orthocide 50W were compared with Parzate and Parzate Liquid-.zinc

sulfate sprays in plots of Picardy bulblets, planting stock and large bulbs where

the Botrytis and Curvularia diseases were encouraged by inoculations and overhead

irrigations. Maneb (Manzate) was more effective than nabam (Dithane D-14 and

Parzate Liquid) and captain (Orthocide). Zineb (Parzate and Dithane Z-78) was

almost as effective as maneb and was definitely more effective than nabam + zinc

sulfate (tank mix as used by most growers), especially in controlling Botrytis.

Captan gave poorer control than the other spray materials. Maneb and zineb were

used at 2-100, captain 50W at 3-100 and nabam at 2 quarts + 3/4 lb. zinc sulfate

in 100 gallons.

Last year's report recommended maneb in controlling Stemphylium leaf spot.

Enough information now is at hand to recommend maneb for controlling Curvularia

and Botrytis. It is clear also that zineb should be used instead of nabam. The

indications are that better disease control and less plant injury will result from

a spray schedule using both zineb and maneb. Zineb will give longer protection than

maneb. Therefore, use zineb in dry weather or before the diseases appear, spraying

once a week. After the disease begins to spread and wetting periods are frequent,

maneb should be alternated with zineb, using 1 1/2 lb. maneb powder in 100 gallons

and spraying twice each week, once with nmneb and once with zineb. When rains

occur frequently and the plants are growing rapidly, especially young bulblets and

flower spikes, it will probably be necessary to spray three times each week, onco

with zineb and twice with maneb.

In order to keep the spray droplets from running together on the new, waxy

growths, a wetting agent is added to the spray mixture. Use only enough wetter to

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cause the droplets to flatten out slightly.

Maneb is able to kill some of the newly-started infections. Therefore, if

a disease is spreading and a prolonged rain occurs when the plants are not re-

cently sprayed, use maneb spray as soon as the plants dry off. The main reliance,

however, should always be placed on the protective action of zineb and maneb be-

cause maneb's curative action is only partial. The aim should be to have the newly-

exposed leaf and flower tissue covered with spray before the rain or dew periods

and to use the curative action of maneb to help out in emergencies.

Maneb has been used by several growers during the past two years with little

or no injury. In this year's spray test the plants were sprayed heavier than

necessary and some injury was seen on the middle section of spikes where spray col-

lected inside the short leaves attached just below the head. This injury may

occur when temperatures are high and the spray dries off slowly. Therefore, the

following precautions should be taken with maneb spray:

Do not over-spray spikes.

If temperatures are over 800F., spray spikes early enough
so they will dry completely before night.

If the plants cannot be sprayed, dust them with zineb or maneb. The dust

mixtures should contain 5 to 6 percent of active ingredient. Light dustings ap-

plied every second or third day are more effective than a heavy dusting made once

a week.

Flower Dip for Botrytis Control

Soft rot of petals and slimy breakdown of spikes in transit and cold storage

can be held fairly ell under control by dipping the heads and part of the stems

in Parzate or Dithane Z-78 spray mixture. Use one pound of the wettable powder in

50 gallons of water. Keep it stirred up and dip the bunches for about two seconds

as soon as they are received at the packing house. Before packing, shake the spray

out of the buds because excess spray inside the bud sheaths may cause burning in

warm weather.

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Other materials which hold down the spread of Botrytis in the package are

Vancide "51", 1/2 pint to 50 gal., and Puratized Agricultural Spray, 1/2 pint in

50 gal. The spike dip is not a substitute for regular and thorough spraying or

dusting in the field because dipping will not stop the development of infections

which have already taken place.

New Strain of Curvularia Fungus

Curvularia infection was found on planting stock of Snow Princess, Valeria,

Hopmans Glory, Morning Kiss and other varieties for the first time in North

Florida. This appears to be a new strain capable of attacking varieties which have

been free of infection. Therefore, spraying for Curvularia control should now in-

clude all varieties. This new strain may explain the severe rotting of bulbs by

Curvularia now showing up.

Fusarium Control

Practically all bulb treatment tests show that flower and bulb yields are

increased by treating the bulbs. This is true for all varieties tested.

Cleaning-time Treatment

Large and medium-sized bulbs should be treated after being cleaned. Dowicide

B has been best in the tests. Wait about 4 to 18 hours after cleaning so that the

scar is dry before dipping. In warm weather soak for 15 minutes in 1 1/2 lb.

Dowicide B in 50 gallons + wetting agent (see below). Increase the time to 30

minutes or the dosage to 2 lb. in cool weather. Increase to 2 lb. if the bulbs

are not to be treated again before planting, as suggested below. At the 1 1/2 to

2 lb. dosage, Dowicide B may burn the exposed bulb tissue, skin-deep, and retard

flowering. However, flower yield and quality apparently are not affected adversely.

If a dust is preferred, use Spergon wettable diluted with an equal amount

of pyrophyllite dust. Bulbs must be dusted immediately after cleaning.

Treat Again Before Planting?

The short Ceresan dip makes it possible to treat the bulbs again before

planting without noticeable chemical injury. Older bulb stocks, badly diseased

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Other materials which hold down the spread of Botrytis in the package are

Vancide "51", 1/2 pint to 50 gal., and Puratized Agricultural Spray, 1/2 pint in

50 gal. The spike dip is not a substitute for regular and thorough spraying or

dusting in the field because dipping will not stop the development of infections

which have already taken place.

New Strain of Curvularia Fungus

Curvularia infection was found on planting stock of Snow Princess, Valeria,

Hopmans Glory, Morning Kiss and other varieties for the first time in North

Florida. This appears to be a new strain capable of attacking varieties which have

been free of infection. Therefore, spraying for Curvularia control should now in-

clude all varieties. This new strain may explain the severe rotting of bulbs by

Curvularia now showing up.

Fusarium Control

Practically all bulb treatment tests show that flower and bulb yields are

increased by treating the bulbs. This is true for all varieties tested.

Cleaning-time Treatment

Large and medium-sized bulbs should be treated after being cleaned. Dowicide

B has been best in the tests. Wait about 4 to 18 hours after cleaning so that the

scar is dry before dipping. In warm weather soak for 15 minutes in 1 1/2 lb.

Dowicide B in 50 gallons + wetting agent (see below). Increase the time to 30

minutes or the dosage to 2 lb. in cool weather. Increase to 2 lb. if the bulbs

are not to be treated again before planting, as suggested below. At the 1 1/2 to

2 lb. dosage, Dowicide B may burn the exposed bulb tissue, skin-deep, and retard

flowering. However, flower yield and quality apparently are not affected adversely.

If a dust is preferred, use Spergon wettable diluted with an equal amount

of pyrophyllite dust. Bulbs must be dusted immediately after cleaning.

Treat Again Before Planting?

The short Ceresan dip makes it possible to treat the bulbs again before

planting without noticeable chemical injury. Older bulb stocks, badly diseased

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stocks and bulbs dug from Stromatinia-infested land should be dipped for 1/2 to

1 minute in the standard N.I.Ceresan solution, 1 lb. per 50 gal. + wetting agent.

This is for bulbs treated with Dowicide B or Spergon at cleaning time.

Preplanting Treatment

Bulbs not treated at time of cleaning should be treated before planting.

Also bulblets should be treated before planting.

For jumbo and large bulbs use one of the following:

1. N.I.Ceresan, 1 lb.-50 gal. + wetting agent, 1 minute. Plant immediately.

Recommended especially for Picardy. (Make fresh solution daily or oftener.

See below).

2. Dowicide B, 3 lb. 50 gal. + wetting agent, 30 minutes. (Increase to 4 lb. in

cold weather). Make fresh solution weekly.

3. Captan 75 (Orthocide) 4 lb. 50 gal. or captain 50 W, 6 lb. 50 gal. Soak

bulbs 30 minutes. Stir the mixture before dipping. Renew mixture every

week or oftener,

Dip planting stock for 1 minute in N.I.Ceresan solution, 1 lb.-50 gal. +

wetting agent. Plant immediately.

Soak bulblets for 30 minutes in N.I.Ceresan solution, 1 lb. 50 gal. +

wetting agent before planting.

Treatments for Sprouted Bulbs

Do not use Dowicide B or 'the 10-minute Ceresar 'treatment on rooted bulbs.

On large and jumbo bulbs with long roots, use captain 75, 3 lb. 50 gal., 15-minute

soak. On small and medium bulbs use the 1-minute dip in N.I.Ceresan.

When To Make Fresh Ceresan Dip

It was found that the strength of N.I.Ceresan solution is gradually lowered

as successive batches of bulbs are dipped. With the 10 to 15 minute dip, discard

old solution when its level in tank drops by 20 percent or one-fifth of the origi-

nal volume. When using the one-minute dip, renew solution after the volume drops

by one-seventh; for instance, from 100 to 85 gallons.

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Wetting Agent for Bulb Dips

It has been difficult for growers to obtain a concentrated wetting agent in

quantity. A Florida distributor is now making "Tergitol" Dispersant TMN available

in 1, 5, and 50-gallon quantities at several retail stores in flower-growing areas

of the State. Use less of TMN than you have used of detergents available at

grocery stores.

The amount of TMN to use will depend on how long bulbs are to be in the dip

solution and on how tight and dry the husks are. One-third of a cup in 50 gallons

is an effective dose for most bulbs.

Other Corm Treatments Tested

Fungicides mentioned last year as promising were generally disappointing

this year when bulbs were soaked in the solutions for shorter periods (30 minutes

or less). These materials include Crag Industrial Fungicide 974, Vancide F-845

and Phygon XL. Peracetic acid was good but not outstanding in disease control.

Experimental Fungicide 5400 diluted 1-1 looked very promising again when dusted

on bulbs after cleaning or before planting. A 30-minute, pre-planting soak in

EMMI (Velsocol 50-cs-46) 1 pint 50 gal. was promising.

Field testing of antibiotics and systemic fungicides has not turned up any-

thing of value for Fusarium control. This phase of the investigation is being

abandoned for the present.

Hot Water Treatment of Bulblets

Bulblets of Picardy, Valeria, Dr. Bennett and Snow Princess were treated in

hot water a year ago as suggested by Bald of Southern California. The planting was

recently dug but no results on disease control could be obtained because the bulbs

were badly infected with Curvularia. Since the plants were kept free of infection

above-ground through the winter and spring, the bulb infection had to come from the

soil. The soil in this field became infested two years ago when a bulblet crop

was killed by Curvularia.

This test did show that dormant bulblets of these varieties can be treated

for 30 minutes in water at 135 F. with very little, if any, reduction in

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germination. Bifblots lug before May or held in cold storage were usually injured

by the treatment because they were not fully dormant. This treatment is being used

commercially in California to grow disease-free gladiolus planting stock. The heat

is supposed to kill Fusariurn as well as other diseases. To obtain maximum benefit

from the treatment, the bulblets must be planted in soil that has not been contami-

nated by a previous crop of gladiolus.

For the benefit of growers who are intorosted in trying the hot4water treat-

ment on gladiolus bulblets, the latest suggestions on procedure are:

1. Use bulblets from clean young stock, preferably planting stock, grown on clean
land and dug after May 15.

2. Cure in shallow layers in an open shed for 8 to 10 weeks after digging.

3. Soak them in cold water for 2 days. Skim off all bulblots which float. This will
eliminate the mummified bulblots rotted by Fusgrium which contain trapped air.
The air Ifsulates against the heat and -prevontsa gOodi kill.

4. Put the bulblets in sacks, only half filled, and soak them for 3 or 4 hours in
formalin solution 1-200 (1 quart formalin in 50 gal. wator). Formalin contains
40% formaldehyde.

5. Then treat at 1350 F. for 30 minutes. Have the water temperature up to 137" or
more so that the cold bulblets will drop the temperature to 1350. Then mnin-
tnin heat by adding hot nwter or by direct hosting of water in tank. Keep hot
water stirred while treating.

6. Romovo the sacks promptly and immodiatoly plunge them into a large volume of
cold water in order to stop the treatment at 30 min.

7. Pour bulblots into clonn trays. Whon dried, place them in cold storage for
about 3 or 4 months.

Soil Treatments for Controlling Fusarium

Some chemicals wore found to kill Fusarium in the soil but none are practical

to use on a field scale as yet. A pot test indicated that flooding the soil with

water for a month or more reduces Fusnrium infection in the subsequent crop. The

deeper the field is covered, the sooner the Fusorium is killed. Some growers who

can manage to flood a field during the summer will be interested in trying this lead.

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Now Type of Rot

Picardy bulbs dug in May and Juno frequently showed a wet rot of husk, bulb-

lots, and sometimes the bulb. The husk and bulblots wore dark brown and a whito or

gray mold was soon on them. Two or more of the following fungi were found in the

bulblots and rotted bulbs: Curvularia, Pollicularia rolfsii (Southern Blight), Fusa-

rium and unidentified fungus. This rot was found mainly on jumbo Picardy as the

bulbs approach maturity. Digging the bulbs a wook or two earlier than usual may

S help to control it.

Curvularia infection of bulbs is becoming more severe each year. The infoc-

ion shows up mainly at the base and sides and frequently along the lines where the

husks are attached. The smaller spots are black, sunken and irregular in shape.

Large spots are sometimes split open long the husk attachment. The evidence sug-

gosts that Curvularia infection may open the way to fusarium infection.

Keep bulblets and planting stocks off land for three years or more after a

crop is attacked by Curvularia. No tests were made on bulb treatment or soil treat-

mont for Curvularia control.