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Publication #PP268

Black Spot of Rose1

Jozer Mangandi and Natalia A. Peres2

Introduction

Black spot is, a fungal disease that affects nearly all rose cultivars worldwide. It is a frequent problem for roses grown outdoors and reduces the quality and life span of the plants. However, the poor performance of roses in Florida can also be associated with various factors such as inadequate fertilization and water deficiency during the warm season, as well as the use of root stocks and scions not well-adapted to Florida's conditions.

Causal Agent and Geographical Distribution

The black spot pathogen, Marssonina rosae (Diplocarpon rosae, sexual stage), is a parasite specific to roses and is considered the most serious disease of roses in Florida. The disease was first reported in Sweden in 1815 and in the United States in 1830. Since then, it has been reported in South America, Canada, Australia, and China, among other countries.

Different genotypes or races of M. rosae, i.e., isolates that infect a specific cultivar or group of cultivars, have been identified. Certain species of roses and cultivars of old garden roses are considered more resistant to the disease than modern cultivars. Modern roses and especially the popular hybrid teas are not only more susceptible to the disease, but also considered high maintenance roses in Florida requiring more attention to disease control, fertilization, and irrigation.

Symptoms

M. rosae produces black spots of about two to 12 mm in diameter usually in the upper surface of the leaves (Fig. 1a). Often, those spots may have irregular, radiate, feathery borders (Fig. 1b). In older lesions, black spore-bearing structures, called acervuli, can be observed as well as white, slimy masses of conidia (Fig. 2a). Yellowing around the lesions on infected leaves can occur and severe defoliation occurs in the most susceptible cultivars. While leaves are the most susceptible part of the plant, stipules and pedicels can also be infected. Spots can also be found also in peduncles, fruits, and sepals. Symptoms of black spot are usually confused with those of Cercospora leaf spot (See EDIS publication Cercospora Leaf Spot of Rose at http://edis.ifas.ufl.edu/PP267).

Figure 1a. 

Leaves of 'Old Blush' rose infected with Marsonina rosae.


Credit:

J. Mangandi, UF-GREC


[Click thumbnail to enlarge.]

Figure 1b. 

Typical lesion of black spot on a rose leaf.


Credit:

J. Mangandi, UF-GREC


[Click thumbnail to enlarge.]

The infection cycle starts when spores are spread by rain or overhead irrigation from leaves or canes infected from the previous season. The conidia must be wet for several hours to infect plant tissues. Symptoms begin to appear in three to 16 days after infection. Mature conidia can be produced 10 to 18 days after infection and initiate a new cycle. Conidia are colorless and two-celled (Fig. 2b). A temperature of 64°F is optimal for black spot development, but conidia germination still occurs from 59 to 81°F. This wide temperature range allows the disease to continue to develop as long as the moisture is adequate during the season.

Figure 2a. 

Black acervuli on a lesion caused by Marsonina rosae. Note the white masses of conidia (arrows), 50x.


Credit:

J. Mangandi, UF-GREC


[Click thumbnail to enlarge.]

Figure 2b. 

Microscopic view of two-celled conidia of Marsonina rosae, 400x.


Credit:

J. Mangandi, UF-GREC


[Click thumbnail to enlarge.]

Control

Black spot can be controlled by planting cultivars with resistance to the disease such as WEKcisbako (HomeRun®) or RADrazz (Knock Out®). These cultivars are, however, susceptible to Cercospora leaf spot. Old garden roses 'Mrs. B.R. Cant' and 'Spice' have shown good levels of resistance to both diseases in our trials. Sanitation practices, such as removal and burning of fallen leaves and pruning of canes late in the winter before new shoots are produced, help reduce the amount of inoculum. Plants should not be allowed to remain wet for long periods of time and overhead irrigation should be avoided or minimized. If this is not possible, plants should be irrigated early in the morning to allow leaves to dry.

For chemical control, an initial application of a protectant fungicide should be made at bud break, followed by bimonthly applications until leaves are completely expanded. During the summer, applications every 7-14 days may be necessary to successfully manage the disease. Fungicides labeled for the control of black spot of roses in Florida are listed in Tables 1 and 2. For managing fungicide resistance, the best strategy is to rotate among products with different modes of action. All fungicides within the same group (with the same number or letter) have the same active ingredient or a similar mode of action. Fungicide resistance is usually low with multi-site inhibitor fungicides group (M).

Tables

Table 1. 

Fungicide products marketed for use by professional pesticide applicators for control of black spot on roses

Active ingredient

Fungicide group

Trade name

Copper ammonium compex

M1

Copper-Count®- N

Copper hydroxide

M1

Champ® Dry Prill, Champ® Formula 2, Kentan® DF

Copper hydroxide + Copper oxychloride

M1

Badge® SC, Badge® X2

Copper oxychloride

M1

Agri Star® COC DF, Agri Star® COC WP

Copper oxychloride + Copper sulfate

M1

C-O-C-S® WDG

Sulfur

M2

Arysta Sulfur 6L, Cosavet-DF®, Kumulus® DF, Stoller® THAT® flowable sulfur, Thiolux Jet, Wettable sulphur, Micro Sulf®, Microthiol® Disperss®

Mancozeb

M3

Dithane® 75DF Rainshield®, Fore™ 80WP Rainshield®, Koverall™, Penncozeb™ 75DF

Maneb

M3

Maneb 75DF, Maneb 80WP

Ziram

M3

Ziram 76DF

Captan

M4

Captan 50WP, Captan 50W, Captec 4L®

Chlorothalonil

M5

Daconil Ultrex® Turf Care®, Daconil Weatherstik®, Echo® 720 T&O, Echo® Zn T&O, Ensign™ 720, Ensign® 82.5% T&O, Initiate® 720, Prokoz Mainsail™ 6.0 F, Prokoz Mainsail™ WDG

Chlorotalonil + thiophanate-methyl

M5+1

Spectro™ 90WDG T&O

Thiophanate-methyl

1

3336® F, Nufarm T-Methyl SPC 4.5 F, Nufarm T-Methyl SPC 50 WSB, Quali-Pro® TM 85 WDG

Myclobutanil

3

Eagle® 20EW, Prokoz, Quali-Pro® Myclobutanil 20 EW T&O

Propiconazole

3

AmTide Propiconazole 41.8% EC, Banner Maxx®, Banner Maxx® II, Fitness™, Nufarm Propiconazole SPC 14.3 MEC, Procon-Z™, Prokoz® Hoist™, Propensity® 1.3ME T&O, Quali-Pro® Propiconazole 14.3

Tebuconazole

3

Clearscape T&O, Quali-Pro® Tebuconazole 3.6F, Monsoon® Turf, Offset™ 3.6F, Torque™

Azoxystrobin

11

Heritage®

Trifloxystrobin

11

Compass® Fungicide, Compass® O 50WDG

Thiophanate-methyl + Iprodine

1 + 2

Nufarm TM+IP SPC

Bacillus subtilis

NC

Cease®

Clove oil+ Rosemary Oil+ Thyme oil

NC

Sporan™, Sporatec®

Mineral Oil

NC

Tritek™

Parafinic Oil

NC

JMS Stylet-oil®

Petroleum Oil

NC

Saf-T-Side®

Potassium bicarbonate

NC

Milstop®

Reynoutria sachalinensis

NC

Regalia®

Neem Oil

NC

Trilogy®

Fungicide Group (FRAC Code): Numbers (1-37) and letters (M) are used to distinguish the fungicidal mode of action groups. All fungicides within the same group (with same number or letter) indicate same active ingredient or similar mode of action. This information must be considered in making decisions about how to manage fungicide resistance. M=Multi-site inhibitors, fungicide resistance is low; NC= not classified. Source: http://www.frac.info/ (Fungicide Resistance Action Committee, FRAC).

Always read a current product label before applying any chemicals.

Table 2. 

Fungicide products marketed toward homeowners for control of black spot on roses

Active ingredient

Fungicide group

Trade name

Copper hydroxide

M1

Hi-Yield ® Copper

Copper Sulfate

M1

Bonide® Copper Dust

Copper Octanoate

M1

Bonide® Liquid Copper, Natural Guard Copper Soap, Ortho® Disease B Gon® Copper Fungicide

Sulfur

M2

Bonide® Sulfur Dust, Ferti-lome® Dusting Sulfur, Green Light, Hi-Yield® Dusting Wettable Sulphur, Ortho® Bug-B-Gon® Rose & Flower Care

Mancozeb

M3

Bonide® Mancozeb

Captan

M4

Bonide® Captan 50WP, Hi-Yield® Captan 50W Fungicide

Chlorothalonil

M5

Bonide® Fungonil, Ferti-lome® Broad Spectrum, Hi-Yield® Vegetable, Flower, Fruit and Ornamental Fungicide, Monterey, Ortho® Disease B Gon™ Garden Fungicide , Monterey Fruit Tree, Vegetable & Ornamental Fungicide

Myclobutanil

3

Spectracide Immunox® Multi-Purpose Fungicide

Propiconazole

3

Ferti-lome® Liquid Systemic Fungicide, Monterey Fungi-Fighter

Tebuconazole

3

Bayer Advanced™ Disease Control for Roses, Flowers & Shrubs

Tebuconazole + Imidacloprid

3 +

Bonide® Rose RX Systemic Drench, Feti-lome® 2-N-1 Systemic

Triforine

3

Ortho® RosePride® Disease Control

Calcium Polysulfide

NC

Hi-Yield® Lime Sulfur Spray

Neem Oil

NC

Bonide® RX 3 in 1, Green Light® Neem Concentrate, Green Light® Rose Defense®, Monterey

Acetamiprid + Triticonazole

NC + 3

Ortho® Bug B Gon® Insect & Disease Control

Acephate + Resmethrin + Triforine

NC + NC + 3

Ortho® RosePride® Insect, Disease & Mite Control

Fungicide Group (FRAC Code): Numbers (1-37) and letters (M) are used to distinguish the fungicidal mode of action groups. All fungicides within the same group (with same number or letter) indicate same active ingredient or similar mode of action. This information must be considered in making decisions about how to manage fungicide resistance. M=Multi-site inhibitors, fungicide resistance is low; NC= not classified. Source: http://www.frac.info/ (Fungicide Resistance Action Committee, FRAC).

Always read a current product label before applying any chemicals.

Footnotes

1.

This document is PP268, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May 2009. Revised July 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Jozer Mangandi, graduate student, Department of Horticultural Sciences; Natalia A. Peres, associate professor, Department of Plant Pathology, Gulf Coast Research and Education Center (REC)--Balm; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label.


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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.