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Group Title: Mimeo report - Bradenton Agricultural Research & Education Center - GC-1972-3
Title: Ascochyta blight of chrysanthemum
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067674/00001
 Material Information
Title: Ascochyta blight of chrysanthemum symptoms and control with fungicides
Series Title: Bradenton AREC mimeo report
Physical Description: 3, 4 leaves : ; 28 cm.
Language: English
Creator: Engelhard, Arthur W
Agricultural Research & Education Center (Bradenton, Fla.)
Publisher: Agricultural Research & Education Center
Place of Publication: Bradenton Fla
Publication Date: 1972
 Subjects
Subject: Chrysanthemums -- Diseases and pests -- Florida   ( lcsh )
Chrysanthemums -- Diseases and pests -- Control -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaf 3).
Statement of Responsibility: Arthur W. Engelhard.
General Note: Caption title.
General Note: "April, 1972."
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00067674
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 71837489

Table of Contents
    Copyright
        Copyright
    Foliage fungicides for Ascochyta blight control
        Page 1
        Page 2
    Bibliography
        Page 3
    Tables
        Page 4
        Page 5
        Page 6
        Page 7
Full Text





HISTORIC NOTE


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Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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Copyright 2005, Board of Trustees, University
of Florida






AGRICULTURAL RESEARCH & EDUCATION CENTER
Bradenton, Florida

Bradenton AREC Mimeo Report GC-1972-3 April, 1972

ASCOCHYTA BLIGHT OF CHRYSANTHEMUM: SYMPTOMS AND CONTROL WITH FUNGICIDES

Arthur W. Engelhard

Ascochyta blight is one of the most important diseases of chrysanthemums in
Florida, affecting flowers, leaves, stems and cuttings. The disease occurs on
plants in the field, in stock beds, and in transit, also under mist propagation,
on cuttings in cold storage and on potted plants.

Much variation occurs in symptom development among cultivars. The cultivars
Mrs. Roy and Oregon are so susceptible that plants may be killed. Disease control
in the field is nearly impossible under conditions ideal for disease development.
Other cultivars such as Beauregard, Iceland, Pink Marble, Yellow Knight and Yellow
Shasta are so resistant that foliage and stem infections seldom occur in the field
even on unsprayed inoculated plants.

Symptoms on the leaves commonly occur as wedge shaped, dark brown to black
lesions starting either at the tips of lobes or between lobes. A chlorotic or
yellow halo surrounds the infected area. Stem lesions are dark brown to black
and may occur at any point but frequently start at nodes. When stem lesions occur
generally in the upper 12 inches of standard type cultivars, the bloom character-
istically curves toward the affected side and does not develop completely.

Leaf and stem infections also result in a "systemic" foliage reaction on some
cultivars. Interveinal chlorosis of leaves occurs on the cultivars Albatross,
Mrs. Roy, Telstar, and Indianapolis following.leaf and stem infections. The
Ascochyta lesion(s) may occur near the base of the plant but the leaf symptoms
may occur on all the leaves, or especially those on the side of the plant directly
above the infection.

The symptoms on the flowers vary considerably. Early infection results in
bud blight in which the entire bud and flower stem or peduncle turns black.
Later flower infections result in one-sided development of flowers from which
the name ray blight originated. Development of disease on the flower receptacle
results in a black decay of the entire flower head.

Infection on cuttings results in a soft, black decay under mist propagation
or in cold storage. The source of the infection may be stock plants or from the
medium in the propagation bench. Ascochyta can be spread to the field even on
lightly infected cuttings.

Spores of the Ascochyta fungus are developed in abundance on all diseased
tissues. Both conidia and ascospores may be produced; the conidia appear to be
the most common spore type produced in Florida. Both kinds of spores are pro-
duced in minute round, black bodies in which they are protected from fungicides
until they are released by rain, overhead irrigation, dew, etc. New conidial in-
fections are visible in the field 24-30 hours after spore release. Optimum dis-
ease development occurs in a temperature range of 65-80 F, but infection can occur
in the range of 45 to 950F.

Foliage fungicides for Ascochyta blight control

Chemicals are discussed on the basis of data obtained on chrysanthemums grown
in ground beds in a saran cloth house at the University of Florida, Agricultural








Research and Education Center, Bradenton. Registration status of the products
is not included in this report.

Benlate benomyll) ,501W is a systemic fungicide that has provided good disease
control at 0.75 to 1.0 lb/100 (Tables 1, 2, 3, 4, 6) with the latter rate pre-
ferred with very susceptible cultivars such as Mrs. Roy. This fungicide performed
well when evaluated for eradicant or after infection fungicidal activity on the
foliage (Table 3), It also provided control of two spotted mites and green peach
aphids when used in a full season program (3). No evidence of phytotoxicity to
foliage or flowers has been observed.

Botran 75W at 0.75 lb/100 was phytotoxic to both leaves and flowers. Data
are not included in the tables.

Daconil 2787 (chlorothalonil) 75W gave Ascochyta control but considerable
variation in disease control was experienced (Tables 1, 2, 3, 4). Rates in the
1.0 to 1.5 lb/100 range would be expected to give good Ascochyta blight control
with the latter the better rate with very susceptible cultivars. Daconil sprayed
alone or in combinations with insecticides is not phytotoxic to foliage but
should not be sprayed more than once on open flowers as repeated applications
are phytotoxic to flowers. Daconil plus Guthion mixtures are phytotoxic to
flowers (3).

Difolatan 4F is a relatively new fungicide that provided good control of
Ascochyta blight at 1 pt/100 (Tables 2, 6). More tests are needed to determine
efficacy, especially safety to flowers.

Dithane M-45 80W or Manzate 200 (zinc ion maneb) provided good disease con-
trol (Tables 1, 2, 3, 4, 5, 6). With very susceptible varieties, 1.5 lb/100 gave
control. No evidence of phytotoxicity to foliage or flowers was observed when
foliage and flowers were sprayed either when they were wet or when they were dry.
Reduction in weight of plants resulting from spraying full season with Citcop 4E
(a liquid copper-containing fungicide) did not occur in Dithane M-45-Citcop 4E
mixtures (Table 5).

Mertect (thiabendazole) 60W, a systemic fungicide, was phytotoxic to chrysan-
themum plants when sprayed at rates as low as 0.125 lb/100 (Tables 1, 2). Drench-
ing 6 inch pots of chrysanthemum plants with 200 ml (7 ounces) two times at 0.25
lb/100 killed the plants (data not shown). Mertect is not safe on chrysanthemum
plants.

Orthocide 50W (Captan 50W) gave good control of Ascochyta blight when sprayed
at 1.5 lb/100 before infection occurred (Tables 1, 2, 3). No phytotoxicity to
the foliage was observed. Rates up to 6 lb/100 were safe to open flowers (2)
except in one experiment when flowers were injured at 2 lb/100 (1).

Citcop 4E (formerly TC 904), a liquid containing 4% copper, provided equal
disease control at both the 1.0 and 0.5 gal/100 (Tables 1, 5). The weight of
the plants sprayed full-season at 0.5 gal/100 at weekly intervals was reduced
but not when Citcop 4E at 0.5 gal/100 was combined with Dithane M-45 80W at
0.5 lb/100. This fungicide-copper combination needs to be evaluated for poten-
tial broadscale selected use for disease control when both fungal and bacterial
diseases are a problem. Complete information on safety to flowers is not avail-
able.

Dithane Z-78 (zineb) 75W, (Table 2), Polyram 80W (Table 2), and Thynon 75W
(Table 6), were each included in only one experiment for the control of Ascochyta
blight. They all showed promise for disease control.









BIBLIOGRAPHY


1. Engelhard, Arthur W. 1967.
themum flowers in Florida.


Safety of fungicides and Meta-Systox-R to chrysan-
Proc. Fla. State Hort. Soc. 80:443-448.


2. Engelhard, Arthur W. 1969. Effects of fungicides and insecticides on flower
quality of commercial chrysanthemums in Florida. Proc. Fla. State Hort.
Soc. 82:381-385.

3. Engelhard, Arthur W. and S. L. Poe. 1971. Combinations of fungicides and
insecticides for control of disease, insects and mites on chrysanthemums.
Proc. Fla. State Hort. Soc. 84: (in press).


TABLE 1.
ASCOCHYTA BLIGHT
SYSTEMIC & PREVENTIVE FUNGICIDES CHRYSANTHEMUMS


AVERAGE OF TWO CULTIVARS1
RATE ASCOCHYTA HEIGHT WEIGHT
FUNGICIDE LB/100 7 DISEASE INCHES POUNDS

Dithane M-45 80W 1.5 weekly 2 25 5.3
S0.75 weekly 3 26 5.4

Daconil 75W 1.5 weekly 3 26 5.3
0.75 weekly 4 26 5.2

Orthocide 50W 1.5 weekly 5 27 5.4
0.75 weekly 11 26 5.3

Benlate 50W 0.75 weekly 13 25 5.2
0.75 2 weeks 14 26 5.5

Citcop 4E 4% copper 1 gal weekly 14 24 3.8
0.5 gal weekly 15 25 4.2

Mertect 60W 1.5 weekly 24 3.1
0.75 weekly -1 24 3.5
1.5 2 weeks -i 24 4.0
0.75 2 weeks -i 25 4.4

Control 100 26 4.9


1Severe chemical injury as marginal chlorosis and necrosis


Planted 9/5/69
Rated 12/16/69
Replications 4
Plants/replication 9


Cultivars No. 2 Red Humdinger
Neptune
Grown in ground beds under saran
cloth


















SYSTEMIC &


ASCOCHYTA BLIGHT
PREVENTIVE FUNGICIDES CHRYSANTHEMUMS


AVERAGE OF TWO CULTIVARS
RATE PER TOTAL ASCOCHYTA LESIONS ON STEMS,
FUNGICIDE 100 GAL LEAVES AND FLOWERS

Difolatan 4F 1.0 pt 42a1
Benlate 50W 1.0 Ib 72ab
Dithane M-45 80W 1.0 Ib 80ab
Orthocide 50 1.0 lb 83ab
Polyram 80W 1.0 Ib 98abc
Daconil 2787 75W 1.0 lb 109 bc
Dithane Z-78 75W 1.0 Ib 156 c
Control Water 338 d
Mertect 60W 1.0 Ib -2
Mertect 60W 0.5 Ib -2
Mertect 60W 0.25 Ib .2
Mertect 60W 0.125 Ib -2
Mertect 60W + ZnSO4.H20 1.0 + 0.1 -2
Mertect 60W + ZnSO4.H20 0.5 + 0.05 .2
Mertect 60W + ZnSO4.H20 0.25 + 0.025 _2


1The small letters in columns or rows indicate Duncan's multiple range
of treatments which do not differ significantly at the 5% level.
2Severe chemical injury on leaves as marginal chlorosis and necrosis.


groupings


Planted 1/20/70
Rated 5/14/70
Replications 4
Plants/replication 9


Cultivars Albatross, No. 2 Red
Humdinger
Grown in ground beds under natural
saran cloth
Sprayed weekly


TABLE 2.














TABLE 3.


ASCOCHYTA BLIGHT
FUNGICIDE-INSECTICIDE MIXTURES CHRYSANTHEMUMS


INSECTICIDES AND RATE/100 GALLONS
FUNGICIDES AND GUTHION 2E DIPEL W PYRENONE 6% CHECK
RATE/100 GALLONS 2.0 PT 0.5 LB 6 FL OZ WATER


Benlate 50W 0.75 Ib
Orthocide 50W 1.5 Ib
Dithane M-45 80W 1.5 Ib
Daconil 75W 1.5 lb
Check Water

Average Ascochyta


Benlate 50W 0.75 Ib
Orthocide 50' 1.5 lb
Dithane 1M-45 80W 1.5 Ib
Daconil 75W 1.5 Ib
Check Water

Average No. salable flowers


ASCOCHYTA BLIGHT 0-9
1,2 2.7 2.5 3.2
1.8 4.7 4.8 4.3
3.5 3.5 3.8 5.0
1.5 5.0 5.8 5.3
5.3 4.3 5.7 7.7

2.7a 4.0 b 4.5 b 5.1 b

SALABLE FLOWERS NO./54 STEMS
46 36 38 31
36 8 11 16
35 21 15 24
25 11 10 21
22 9 8 4


17 b


16 b


AVG. ASCOCHYTA
RATING
2.4a1
3.9 b
3.9 b
4.4 b
5.7 c


AVG. NO.
SALABLE FLOWERS
38a
18 bc
24 b
17 bc
11 c


19 b


The small letters in columns or rows indicate Duncan's multiple range groupings
of treatments which do not differ significantly at the 5% level.


Planted 2/2/71
Rated 5/18/71
Replications 3
Plants/replication 9


Cultivar Mrs. Roy
Grown in ground beds under natural
saran cloth
Sprayed weekly after infection became
apparent following field inocu-
lation







TABLE 4.


ASCOCHYTA BLIGHT
FUNGICIDE-INSECTICIDE MIXTURES CHRYSANTHEMUMS


INSECTICIDE TREATMENT AND RATE PER 100 GAL
FUNGICIDE AND AZODRIN 3.2E DIAZINON 50W DIPEL W GARDONA 75W GUTHION 2E PYRENONE 6% AVERAGE
RATE PER 100 GALLONS 1.5 PT 2 LB 0.5 LB 0.7 LB 2.0 PT 7 LIQ OZ %

PERCENT ASCOCHYTA
Benlate 50W, 1 lb -2 8 18 7 6 5 9a1
Daconil 75W, 2 lb 2 8 17 7 5 12 10a
Dithane M-45 80W, 2 lb -2 10 19 11 5 10 lla
Orthocide 50W, 2 Ib -2 5 11 7 2 11 7a
Check, H20 76 76 37 51 74 63 b

Average % Ascochyta -2 21 b 28 b 14a 14a 22 b


The small letters indicate
5% level.

Chemical injury on foliage

Planted 9/8/70
Rated 12/15/70
Replications 2
Plants/replication 9


Duncan's Multiple Range groupings of treatments which do not differ significantly at the


too severe to make disease counts.

Cultivars Mrs. Roy, Inferno
Grown in ground beds under natural saran cloth
Sprayed weekly






TABLE 5.


ASCOCIHTA BLIGHT
FUNGICIDES CHRYSANTHEMUMS


RATE PER TOTAL NO. AVG. HT. AVG. WT.
NO. TREATMENT 100 GALLONS OF LESIONS IN/PLANT OZ/PLANT

1 Dithane M-45 80W 1.0 lb 155 35 7.5
2 Citcop 4E (4% copper) 0.5 gal 169 35 6.7
3 Dithane M-45 + Citcop 4E 0.5 Ib + 0.5 gal 183 35 7.7
4 Dithane M-45 80U 0.5 Ib 189 34 7.2
5 Bay 78175 systemic fung. 1.0 lb 235 35 7.0
6 Control 389 35 6.8


Planted 1/20/70 Cultivars Mrs. Roy, Albatross
Rated 5/11/70 Grown in ground beds under natural
Replications 3 saran cloth
Plants/replication 9 Sprayed weekly
Inoculated Sprayed with Ascochyta conidia
on 3/12, 3/22 and 4/10/70




TABLE 6

ASCOCHYTA BLIGHT
FUNGICIDES CHRYSANTHEMUMS


RATE PER AVERAGE OF 2 CULTIVARS
NO. TCr..TIIT 100 GAL PERCENT ASCOCYTA

1 Ditbane M-45 80W + Trem 014 1.0 Ib + 0.5 pt 32
2 Difolatan 4F 1.0 pt 45
3 Difolatan 4F 0.5 pt 67
4 Thynon 75W 1.0 lb 68
5 Benlate 50W 0.5 lb 73
6 Dithane M-45 80W 1.0 Ib 84
7 Control 100


Planted 9/8/70
Rated 12/16/70
Replications 3
Plants/replication 12
Inoculated Sprayed with Ascochyta conidia
on 11/10/70, 11/13/70, 11/20/70
and 12/1/70. Disease severe


Cultivars Mrs. Roy, Showoff
Grown in ground beds under natural
saran cloth
Sprayed weekly no phytotoxicity
observed




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