Group Title: TREC-H research report - Tropical Research and Education Center-Homestead ; SB-86-1
Title: Chemical control of snap bean rust at Homestead, Florida in 1986
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Permanent Link: http://ufdc.ufl.edu/UF00067851/00001
 Material Information
Title: Chemical control of snap bean rust at Homestead, Florida in 1986
Series Title: Homestead TREC research report
Physical Description: 8 leaves : ; 28 cm.
Language: English
Creator: Pohronezny, Ken, 1946-
Dankers, Wilbur
Gregory, Nancy Fisher
TREC (Agency)
Publisher: IFAS, University of Florida, Tropical Research and Education Center (TREC)
Place of Publication: Homestead (Fla.)
Publication Date: 1986
 Subjects
Subject: Beans -- Diseases and pests -- Control -- Florida   ( lcsh )
Rust fungi -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Ken Pohronezny, Wilbur Dankers, and Nancy Fisher Gregory.
General Note: "08 September 1986"
 Record Information
Bibliographic ID: UF00067851
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 72823612

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Agricultural Sciences and should be
used only to trace the historic work of
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Copyright 2005, Board of Trustees, University
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Homestead TREC Research Report SB86-1 4 WB 6

Chemical Control of Snap Bean Ru SEP 25 1986
at Homestead, FLorida in 198

KEN POHRONEZNY, Associate Professor, WILBUR DA uK IS.B SOli.o floib
Scientist II, and NANCY FISHER GREGORY, Agrici -ra1 Tchnjia&,
IFAS, University of Florida, Tropical Researce and Education
Center (TREC), Homestead.
INTRODUCTION

Snap bean rust, caused by the fungus Uromyces phaseoli
(Rehen) Wint., continues to be a serious problem for commercial
producers in south Florida. Powdery mildew is also an
occasional problem in the spring crop. Therefore, these studies
were conducted to evaluate the efficacy of several registered
and experimental compounds for control of rust, powdery mildew,
and other foliar diseases.
MATERIALS AND METHODS

Beans, cv Sprite, were direct-seeded into a Rockdale series
soil (pH approximately 7.8) at the TREC, Homestead on 13
February 1986. Some replanting was necessary on 5 March 1986
due to losses in the frost of 1 March. Test plots consisted of
4 rows, 20 ft (6.1 m) long on 3 ft (0.91 m) centers. Six
treatments were replicated 4 times in a randomized complete
block design. Thirty ft (9.1 m) were left between blocks to
reduce interplot interference. Specific treatments are shown in
Table 1.

All chemicals were applied with a tractor-mounted hydraulic
boom sprayer at a pressure of 180 Ib/in (124 nt/cm ) delivering
80 gal finished spray/acre (745 L/ha). The arrangement of cone
nozzles was 5 per row (2 drop nozzles included).

The water control, maneb and sulfur tank mix, maneb, sulfur
treatments were applied 20 March, 27 March, 3 April, 10 April,
17 April, 25 April, and 29 April. The bitertanol and HWG 1608
treatments were applied 20 March, 27 March, 10 April, and 25
April.

Weed control consisted of a pre-emergence application of
trifluralin at 0.75 lb a.i./acre (0.84 kg a.i./ha) and
metolachlor at 1.15 lb a.i./acre (1.29 kg a.i./ha), and periodic
mechanical cultivation and hard-weeding. Benomyl applications
were made as recommended for white mold control, and
applications of insecticide (primarily methamidophos and
cyfluthrin) were made as needed, based on field scouting
it results.








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Table 1. Fungicide treatments in rust control experiment, Homestead Florida in 1986.



Active Active
Treatment ingredient ingredient Number, of
generic chemical trade name (1b a.i ./acre) (kg a.i./ha) applications

1) H20 (control) Water 7


2) Bitertanolx Baycor 50WP 0.125 0.14 4

3) HWG 1608 0.019 0.021 4

4) Maneby & sulfur Dithane M-22
Special 80WP
& THAT flowable 1.2 & 2.0 1.34 & 2.24 7

5) Maneb Dithane M-22
Special 80WP 1.2 1.34 7

6) Sulfur THAT flowable 2.0 2.24 7

XBitertanol applications were made with 0.5.pt/acre (0.58 L/ha) p.enatrator as an adjuvant.
YManeb applications were made with 8oz/acre (545 ml/ha) Nu-film 17 as an adjuvant.









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Rust disease severity was evaluated 3 times in the later
stages of the experiment. Rust pustules were counted on the
underside of 5 midcanopy trifoliate leaves per plot. On 2
dates, Horsfall-Barratt ratings were also taken of disease
severity on both the adaxial and abaxial surfaces of these same
leaves.

Plots were harvested once on 5 May. Twenty row-ft (6.1
row-m) from the interior rows were used for yield
determinations. Records were taken of the weight of marketable
beans and culls. The culls were further sorted into several
defect categories and the percent culls were calculated.

All disease severity and yield data were analyzed by
analysis of variance, followed by a series of preplanned
single-degree-of-freedom orthogonal contrasts. Data for number
of pustules were converted to (log 1+1) and the percent cull
data to arcsineVx+0.5 equivalents before analysis.
RESULTS AND DISCUSSION

The ergosterol biosynthesis inhibitor fungicides were
superior to the other fungicides for control of bean rust
(Tables 2 and 3). For example, on 25 April, the mean number of
rust pustules in the bitertanol and HWG 1608 plots were 70% and
11%, respectively, of those in the maneb plus sulfur tank-mix
plots. On 2 May, bitertanol and HWG 1608 reduced postule
numbers by 95% and 97%, respectively, over the control (Table
2).

The numbered compound HWG 1608 was more efficacious than
bitertanol (Tables 2,3,4) for the first two sampling dates.
Both the mean number of rust pustules (Table 3) and the
Horsfall-Baratt ratings on both upper and lower leaf surfaces
(Table 4) were significantly lower (P=0.01) for HWG 1608
compared to bitertanol. Since bitertanol and HWG 1608 were used
only 4 times, compared to 7 sprays of the standard fungicides,
both materials should be very competitive economically.

Use of sulfur alone seemed as effective for control of rust
as a tank-mix of maneb and sulfur. In some cases, maneb by
itself did not appear to do as well as either sulfur or the
maneb + sulfur tank-mix. On 25 April and 2 May,
Horsfall-Barratt ratings on abaxial leaf surfaces were
significantly lower (P=0.05) in sulfur-treated plots that in
maneb-treated plots (Table 4). It may be that the major
advantage of tank-mixing maneb and sulfur when spraying snap
beans is not enhancement of rust control, but rather an increase










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in the spectrum of foliar disease control. In particular, maneb
s needed to prevent serious damage from sporadic outbreaks of
Iternaria leaf spot, caused by Alternaria alternate, since
ulfur offers little protection against this disease.

No significant differences were found between treatment
means for marketable and total yield (Table 5). Incidence of
culls due to disease was generally low and few differences
between treatments were found. However, the incidence of
powdery mildew pod damage was significantly higher in plots
treated with maneb alone compared to plots treated with either
sulfur alone or the maneb + sulfur tank-mix.

Both bitertanol and HWG 1608 did an excellent job of
controlling pod damage by the powdery mildew fungus.

The results of these tests indicate the potential for HWG
1608 and bitertanol in the disease management programs of South
Florida snap bean growers. They provided superior control of
rust and powdery mildew compared to the maneb and sulfur
standards with fewer applications, and with no observable
phytotoxic effects on the crop.








L










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Table 2. Control of snap bean rust in experimental plots at Homestead, Florida in 1986.


18 April 25 April 2 May
number of number of Horstall/Barratty number of Horsfall/Barratt
Treatments pustules pustules adaxial abaxial pustules adaxial abaxial

Control (water) 727 1694 5.75 5.75 4237 6.25 7.50

Bitertanol 322 581 4.75 4.50 235 2.00 2.25

HWG 1608 51 96 2.25 2.00 120 2.25 2.50

Maneb & sulfur 368 829 4.75 4.75 2279 5.75 6.25

Maneb 1576 2062 6.00 6.00 3417 6.50 7.25

Sulfur 820 981 5.00 5.00 3336 6.25 6.50
XValues are numbers of pustules on abaxial surface of five midcanopy leaves plot and are the means of
four replications.

YValues are the means of four replications of leaves used for pustules counts.









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Table 3. Preplanned single degree of freedom orthogonal contrasts, orthogonal contrast sum of
squares (CSS), and F-test values (F) for snap bean rust severity in experimental plots at
Homestead, Florida 1986.


Statistics for transformed (1og10+1) of rust pustulesx


18 April 25 April 2 May
Preplanned contrasts CSS F CSS F CSS F
Control vs. all
treatments 0.1732 1.3453 0.4465 9.8497** 1.7184 24.2942**

Sterol inhibitors vs
other fungicides 3.1622 24.5516** 2.5696 56.6826** 8.5760 121.2448**

Bitertanol vs HWG
1608 1.8818 14.6102** 1.1858 26.1573** 0.2887 4.0829

Maneb + sulfur vs
maneb or sulfur 0.8970 6.9648* 0.1872 4.1308 0.2320 3.2808

Maneb vs sulfur 0.1799 1.3975 0.2177 4.8044*', 0.0001 0.0028

XBased on numbers of pustules on abaxial surface of five midcanopy trifoliate leaves, for four
replications.
Denotes significant differences) at P=0.05.

**Denotes significant differences) at P=0.01.
**Denotes significant differences) at P=0.01.


I I





C.


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Table 4. Preplanned single degree of freedom orthogonal contrasts, orthogonal contrast sum of squares
(CSS) and F-test values (F) for snap bean rust severity in experimental plots at Homestead, Florida 1986.

Statistics for Horsfall/Barratt Ratingsx
25 April 2 May
adaxial abaxial adaxial a b axial
Preplanned contrasts CSS FCSS FT CSS F CSS F

Control vs all
treatments 4.80 9.60** 5.63 16.34** 9.63 39.37** 20.83 52.08*

Sterol inhibitors vs
other fungicides 14.70 29.40** 19.20 55.71** 78.41 320.47** 91.88 229.69*

Bitertanol vs HWG
1608 12.50 25.00** 12.50 36.27** 0.12 0.51 0.12 0.31

Maneb + sulfur vs
maneb or sulfur 1.5 3.0 1.5 4.35 1.04 4.26 1.5 3.75

Maneb + sulfur 2.0 4.0 2.0 5.80* 0.12 0.51 2.0 5.00*
xBased on Horsfall/Barrett ratings on adaxial and abaxial surfaces of five midcanopy trifoliate
leaves, for four replications.

Denotes significant differences) at P=0.05.

**Denotes significant differences) at P=0.01.









-8-


Table 5. Yields and cull incidence in snap bean rust control experiment, Homestead,
Florida in 1986.

Yield (g/plot) Cull incidence (%)

Rhizoctonia Powdery Alternaria
Treatments Marketable Total pod rot mildew pod blemish

Control (water) 2265 2338 1.8 0.79 0.42

Bitertanol 3035 3108 1.6 0.48 0.30

HWG 1608 2980 3020 0.55 0.43 0.17

Maneb + sulfur 2730 2818 2.7 0.12 0.17

Maneb 2478 2641 1.6 3.8 0.63

Sulfur 2415 2463 1.5 0.45 0.06
XMeans of 4 replications, based on harvest of 20 row-ft of beans.




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