Group Title: CFREC-Apopka research report
Title: 1990 fungicide trials for control of Alternaria, Helminthosporium, Phytophthora, and Rhizoctonia diseases of ornamentals
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Permanent Link: http://ufdc.ufl.edu/UF00074491/00001
 Material Information
Title: 1990 fungicide trials for control of Alternaria, Helminthosporium, Phytophthora, and Rhizoctonia diseases of ornamentals
Series Title: CFREC-Apopka research report
Physical Description: 8 p. : ill. ; 28 cm.
Language: English
Creator: Chase, A. R ( Ann Renee )
Central Florida Research and Education Center--Apopka
Publisher: University of Florida, Central Florida Research and Education Center-Apopka
Place of Publication: Apopka FL
Publication Date: 1990
 Subjects
Subject: Plants, Ornamental -- Diseases and pests -- Control -- Florida   ( lcsh )
Fungicides -- Testing -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: A.R. Chase.
General Note: Caption title.
 Record Information
Bibliographic ID: UF00074491
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 70118224

Full Text

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1990 Fungicide trials for control of Alternaria, Helminthosporium,
Phytophthora, and Rhizoctonia diseases of ornamentals

A. R. Chase'

University of Florida, IFAS,
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Report, RH-90-25

Research conducted during the past 10 years on disease control for ornamental plants
has included screening new fungicides and bactericides as well as testing expansion of labels
necessary for existing products. Several new fungicides have become available for testing
on ornamental crops during the past two years. These chemicals were tested on some of
the following diseases: Alternaria leaf spot of schefflera, Helminthosporium leaf spot of
areca palm, Phytophthora stem rot of aphelandra, Rhizoctonia aerial blight of Boston fern,
and Rhizoctonia stem rots of impatiens and vinca.

ALTERNARIA LEAF SPOT OF SCHEFFLERA

Alternaria leaf spot of scheffleras (Brassaia actinophylla) is caused byAltemariapanax
which is also a pathogen of aralias and dwarf schefflera. Plants were sprayed with fungicides
to the point of drip on a weekly interval between 27 September and 11 October.
Treatments included triflumizole at two rates (Terraguard 50WP at 4 or 8 oz/100 gal), an
experimental compound (G696 at 30 oz/100 gal), and iprodione (Chipco 26019 50WP at 24
oz/100 gal). Plants were inoculated with spores of the pathogen on 2 October and the
number of spots per plant was determined on 12 October. Only Chipco gave a significant
degree of disease control (Figure 1). G696 caused severe stunting and marginal chlorosis
and necrosis.

HELMINTHOSPORIUM LEAF SPOT OF ARECA PALM

Helminthosporium leaf spot is the most common disease of areca palm
(Chrysalidocarpus lutescens) and is frequently caused by Exserohilum rostratum
(=Helminthosporium rostratum). In the 1990 test, two rates of triflumizole (Terraguard
50WP, 4 and 8 oz/100 gal), one rate of mancozeb (Manzate 200 80WP, 1.5 lb/100 gal), and
one rate of iprodione (Chipco 26019 50WP, 1 lb/100 gal) were tested. Fungicides were
applied as a spray on a weekly interval from 28 June to 9 August. Plants were naturally
infected and number of lesions per plant was recorded on 10 August. Best disease control
was achieved with Manzate 200, Chipco 26019 or Terraguard at the lower rate (Figure 2).
Control with the higher rate of Terraguard was not acceptable. It is not clear why a lower


'Professor of Plant Pathology, Central Florida Research and Education Center Apopka,
2807 Binion Road, Apopka, FL 32703.
1 /









rate of this compound gave good disease control when a higher rate failed to give any
disease control.

PHYTOPHTHORA STEM ROT OF APHELANDRA

Phytophthora stem rot of many foliage plants is caused by Phytophthora parasitica.
In 1990, a trial on zebra plant (Aphelandra squarrosa 'Dania') was performed with both
foliar sprays and drenches of a number of fungicides. Sprays were applied to the point of
drip and drenches were applied at the rate of 1 pint per ft2 on 4 September. Fungicide
treatments applied as a foliar spray included: a combination of fosetyl aluminum and
iprodione (Aliette 80WP at 2.5 lb and Chipco 26019 50WP at 1.0 lb/100 gal), Aliette 80WP
alone at 2.5 or 5.0 lb/100 gal, and Aliette 80WG at 5.0 lb/100 gal. Fungicides applied as
drenches were a combination of fosetyl aluminum and iprodione (Aliette 80WP at 0.4 lb and
Chipco 26019 50WP at 0.5 lb/100 gal), Aliette 80WP alone at 0.4 or 0.8 lb/100 gal, Aliette
80WG at 0.8 lb/100 gal, metalaxyl (Subdue 2E at 2.0 oz/100 gal), and a combination
product of benomyl and metalaxyl (Varsity 42WP at 1 lb/100 gal). Plants were inoculated
with a mycelial slurry (added to the potting medium) on 10 September and symptoms were
monitored every three days for about three weeks. Disease severity was rated from 1 (no
disease) to 5 (dead). Symptoms of stem rot are given for 24 September (Figures 3,4). Best
disease control was achieved with the foliar spray of Aliette 80WP at the high rate, the
drench of Aliette 80WP at the high rate, and the spray and drench of Aliette 80WG. The
combination of Chipco and Aliette as a drench and the Aliette 80WP as a drench at the low
rate gave poorest disease control. Other fungicides gave intermediate degrees of control.
Unfortunately, by the end of the trial none of the fungicides gave significant disease control
(statistically), although all plants treated with the Aliette 80WG as a spray remained healthy.

RHIZOCTONIA DISEASES OF BOSTON FERN, VINCA AND IMPATIENS

A series of trials was conducted on Rhizoctonia diseases of ornamentals since these
diseases are not all caused by the same organism and different plants show different
symptoms. Two types of trials on Rhizoctonia diseases are included in this report. The
most common disease caused by Rhizoctonia on Boston fern (Nephrolepis exaltata) is called
aerial blight. The second trial series employed two bedding plants, vinca (Catharanthus
roseus and common impatiens (Impatiens Wallerana) which commonly suffer from
Rhizoctonia stem rot. Plants were obtained from commercial producers, established in
Vergro potting medium and grown under standard conditions. Ten single plant replicates
were used for each of the treatments in each trial.

Control of aerial blight of Boston fern was attempted as a foliar spray with a variety
of chemicals (Figure 5). Plants were sprayed weekly from 27 September to 11 October.
Treatments included two rates of triflumizole (Terraguard 50WP at 4 and 8 oz/100 gal), one
rate of an experimental compound (G696 at 30 oz/100 gal), and one rate of benomyl
(Benlate 50DF at 16 oz/100 gal). Inoculation with an isolate of R. solani AG4 from fern
occurred four days after the first fungicide treatment. The percent of the plant foliage with









symptoms of aerial blight was recorded on 15 October. Excellent control was seen on plants
sprayed with any fungicide (Figure 5). Both rates of Terraguard gave a high degree of
control although G696 and Benlate 50DF gave a slightly higher degree of control. Ferns
sprayed with G696 showed severe phytotoxicity as evidenced by stunting, marginal chlorosis
and marginal necrosis.

Rhizoctonia stem rot trials were conducted with vinca and common impatiens.
Fungicides were applied as drenches (about 1 pint/ft2) on 28 June (first trial) or 2 August
(second trial). Inoculations with a mycelial slurry occurred 4 days after the fungicide
application. Fungicides used in the first trial were two formulations of PCNB
(pentachloronitrobenzene) (Terraclor 75WP at 4 oz/100 gal) and (Terraclor 50DF at 6 oz/
100 gal) and triflumizole (Terraguard 50WP at 4 oz/100 gal). The percentage of the plant
with stem rot was rated between 1 and 2 weeks after inoculation for impatiens and about
2 to 3 weeks after inoculation for vinca. Some disease control was achieved in the week
following the inoculation but it rapidly collapsed as disease pressure increased for both
impatiens and vinca (Figure 6). Since disease pressure may have been too high to properly
evaluate control of Rhizoctonia stem rot on these bedding plants, a second test was
performed.

The same treatment was used in the second trial with the following two new ones
added: benomyl (Benlate 50DF at 16 oz/100 gal), and a combination product of benomyl
and metalaxyl (Varsity 42WP at 16 oz/100 gal). In this trial, fungicides were applied on 2
August and plants were inoculated with a lower dosage of the pathogen on 6 August. As
with the first trial disease control for the impatiens was initially good but generally failed
to maintain control for even four weeks. Both Varsity 42WP and Benlate 50DF gave
excellent disease control with the other fungicides giving slight control (Figure 7). With the
exception of Terraguard, stem rot of vinca was more readily controlled with all fungicides,
giving a significant degree of control (Figure 7). Apparently, none of these fungicides can
control Rhizoctonia stem rot on these bedding plants when disease pressure is high.
Prevention of this disease through use of clean plants, pots and potting media is the most
important method of control.









CONCLUSIONS


1. Chipco 26019 50WP gives excellent control of Alternaria leaf spot of schefflera.

2. Manzate 200 80WP, Chipco 26019 50WP, and Terraguard 50WP (at 4-8 oz based on
previous year's data) give excellent control of Exserohilum leaf spot of Areca
palm.

3. Phytophthora stem rot of zebra plant was best controlled by a foliar spray of a new
formulation of Aliette (80WG).

4. Benlate 50DF and Terraguard 50WP gave excellent control, without phytotoxicity,
of aerial blight on Boston fern.

5. Controlling Rhizoctonia stem rot on impatiens and vinca is dependent on disease
pressure. Under conditions of very high pressure none of our fungicides can control
this disease.









Figure 1. Effect of fungicides on severity of Alternaria leaf spot of schefflera (Brassaia
actinophylla) caused by Altemaria panax.


No. lesions/plant


Noninoculated Inoculated Terraguard Terraguard G696 Chlpco 26019
4 oz 8 oz 30 oz 24 oz


Treatment
Figure 2. Effect of fungicides on severity of Helminthosporium leaf spot of areca palm
(Chrysalidocarpus lutescens) caused by Exserohilum rostratum.


No. lesions/plant


Water Terraguard Terraguard Manzate 200 Chlpco 26019
4 oz 8 oz 24 oz 24 oz
Treatment










Figure 3. Effect of fungicide sprays on severity of Phytophthora stem rot of zebra plant
(Aphelandra squarrosa) caused by Phytophthora parasitica.


Disease severity


Noninoculated Inoculated Chlpco Aliette Allette Allette
Allette 80WP80WP 2.5 Ib 80WP 5.0 Ib 80WG 5.0 Ib

Treatment
Disease severity was rated from 1
(no symptoms) to 5 (dead).



Figure 4. Effect of fungicide drenches on severity of Phytophthora stem rot of zebra plant
(Aphelandra squarrosa) caused by Phytophthora parasitica.


Disease severity
3.5

3-

2.5-

2-

1.5-



0.5 -


Nonlnoc Inoc Chlpco Al 80WP Al 80WP AI 80WG Subdue
Al 80WP 0.4 Ib 0.8 Ib 0.8 Ib 2 oz
Treatment
Disease severity was rated from 1
(no symptoms) to 5 (dead). 6


varsity
1.0 Ib









Figure 5. Effect of fungicides on severity of Rhizoctonia aerial blight of Boston fern
(Nephrolepis exaltata) caused by Rhizoctonia solani.


Percent foliage with symptoms


Noninoculated Inoculated


Terraguard Terraguard
4 oz 8 oz


- -M


G696
30 oz


Benlate
16 oz


Treatment
Figure 6. Effect of fungicides on severity of Rhizoctonia stem rot of common impatiens
(Impatiens Wallerana) and vinca (Catharanthus roses) caused by Rhizoctonia solani
AG4 Test 1.




Disease severity


S Impatiens I Vinca











1 i


Inoculated Terraclor
75WP


Terraclor Terraguard
50DF 4 oz


Treatment


Disease severity was rated from 1
(no disease) to 5 (dead)


Noninoc
lated










Figure 7. Effect of fungicides on severity of Rhizoctonia stem rot of common impatiens
(Impatiens Wallerana) and vinca (Catharanthus roseus) caused by Rhizoctonia solani
AG4 Test 2.
Percent infection
1inn


H Impatiens I Vinca














IncltdTralr TralrTraur elt


80-


60-


40-


20-


Noninoc
lated


Inoculated Terraclor Terraclor Terraguard Benlate
75WP 50DF 4 oz 16 oz

Treatment


Varsity
16 oz




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