Managing Gladiolus Rust in Mexico with Fungicides A. VALENCIA-BOTÍN, Univ de Guadalajara, Guadalajara, Jalisco, MEXICO; J. W. Buck, University of Georgia, Griffin, GA, U.S.A;

S. N. Jeffers, Clemson University, Clemson, SC, U.S.A.; C. L. Palmer, IR-4, Princeton, NJ, U.S.A. Phytopathology 101:S181

State Harvested area (ha)

Production (ton)

Mean price at the producer level

(Mexican $/Ton)

Production value (in thousand)

Mexican Pesos U.S.A. $ z Guerrero 402 271,200 $156 $42,380 $3,620 Mexico 1,037 1,118,362 $173 $193,388 $16,521 Michoacan 501 407,795 $90 $36,646 $3,131 Morelos 657 768,530 $141 $108,577 $9,275 Oaxaca 11 5,503 $251 $1,381 $118 Puebla 954 1,653,200 $306 $505,259 $43,163 Veracruz 90 77,850 $125 $9,731 $831 Total 3,652 4,302,440 $209 $897,362 $76,659

Uromyces transversalis, the causal agent of gladiolus rust, is an invasive pathogen of gladiolus. U. transversalis infects other members of the Iridaceae family including Crocosmia, Tritonia, and Watsonia. Gladiolus is grown in the U.S.A. as an ornamental plant for cut flowers and for commercial and residential landscaping, while Crocosmia and Tritonia are more recent introductions for commercial and residential landscapes. The wholesale or farmgate value of gladiolus cut flower production in the U.S.A. is $24 million (2009 USDA NASS Census of Horticulture, 2010) with the bulk of this production occurring in Florida. Gladiolus flowers are imported into the U.S.A. from several countries including Mexico. The farmgate value for gladiolus production in Mexico in U.S.A. dollars is $77 million. U. transversalis is endemic in Mexican gladiolus production areas and the importation of this fungus along with cut flowers is an identified introduction pathway of concern. When this rust disease is found in the U.S.A., gladiolus plants are destroyed and growers undergo a regime of fungicide applications to eradicate U. transversalis. Currently, U. transversalis has been found infecting gladiolus in California, Florida, and Minnesota. In California, these infections have been restricted to residential and landscaped areas. In Florida, infections have been discovered in production fields. Crop destruction and use of preventative application of fungicides have been the tools to eradicate this invasive disease. Fungicides in the triazole class along with chlorothalonil and azoxystrobin are the primary fungicides applied in Florida. Triazoles and strobilurins target single sites for their modes of action and thus are more susceptible to the development of resistance in target populations. The results presented here are the first in a series of planned experiments to identify additional effective fungicides which are important for the long term management of gladiolus rust.

Fall 2010. During Sept. to Nov., 2010, two trials were conducted in commercial gladiolus fields in Cuautla, Morelos and Atlixco, Puebla states of Mexico. Natural infections were augmented with inoculations of U. transversalis spores. Four applications of 11 fungicides (Tables 2 and 3) plus two controls (non-inoculated and inoculated untreated plants) were made every 14 days using a hand-held CO2 backpack sprayer. Disease severity in each plot was recorded each week for 7 weeks after first application. Spring 2011. From Mar. to May, 2011, one trial was conducted in commercial gladiolus field in Tlayacapan, Morelos, Mexico. Natural infections were augmented with inoculations of U. transversalis spores. Six applications of 14 fungicides (Table 4) plus two controls (non-inoculated and inoculated untreated plants) were made every 14 days using a hand-held CO2 backpack sprayer. Disease severity in each plot was recorded each week for 10 weeks after first application.

Fall 2010, Cuautla, Morelos Inoculum pressure was high with disease severity starting at 9.8% and finishing at 76.8% in the non-inoculated, non-treated plots (Table 2). All fungicide treatments significantly reduced disease severity compared to the inoculated, non-treated plots. Disease development was least with three triazole fungicides: epoxiconazole, propiconazole and tebuconazole. The addition of boscalid to pyraclostrobin did not improve performance.

Active Ingredient(s)

Trade Name

Product rate per liter (per 100 gal)

Disease Severity AUDPC 10/1 z 10/16 10/30 11/13

Azoxystrobin Amistar 750 mg (10.3 oz) 8.6 a 13.8 b 27.9 cd 45.5 bc 171 b Boscalid + Pyraclostrobin Cabrio 2g/L (27.3 oz) 13.7 a 20.0 b 34.2 bcd 51.0 b 208 b

Epoxiconazole Opus 1.875 ml (24.6 fl oz) 9.1 a 21.3 b 25.9 cd 23.3 d 135 c Fluoxastrobin Vigold 750 mg (10.3 oz) 8.5 a 19.5 b 35.0 bcd 58.5 b 219 b Kresoxim-methyl Stroby 625 mg (8.5 oz) 7.4 a 22.8 b 45.4 b 51.8 b 223 b Myclobutanil Rally 200 mg (2.7 oz) 8.0 a 19.0 b 30.0 bcd 49.3 b 192 b Oxycarboxin Plant Vax 3750 mg (51 oz) 6.8 a 16.5 b 33.8 bcd 44.0 bc 186 b Propiconazole Tilt 2.5 ml (32.8 fl oz) 10.5 a 17.0 b 22.3 d 29.8 cd 138 c Pyraclostrobin Headline 1 ml (13.1 fl oz) 10.5 a 26.8 b 41.1 bc 53.8 b 234 b Tebuconazole Tebucur 1.5 ml (19.7 fl oz) 8.3 a 17.8 b 27.6 cd 28.8 cd 140 c Trifloxystrobin Flint 625 mg (8.5 oz) 12.8 a 20.0 b 40.0 bc 51.3 b 220 b Non-inoculated Control 9.8 a 48.5 a 66.0 a 76.8 a 356 a Inoculated Control 13.8 a 46.0 a 65.8 a 79.8 a 354 a

Fall 2010, Atlixco, Puebla Inoculum pressure was high with disease severity starting at 16.8% and finishing at 75.3% in the non-inoculated, non-treated plots (Table 3). Starting Oct. 16, epoxiconazole and tebuconazole exhibited statistically less disease severity than the inoculated, untreated plots. As the season progressed, propiconazole and trifloxystrobin reduced disease, and by Nov. 13, 2010 all treatments significantly reduced disease severity, with epoxiconazole providing the best season-long efficacy.

Active Ingredient(s)

Trade Name

Product tate per liter (per 100 gal)

Disease Severity AUDPC 10/1 10/16 10/30 11/13

Azoxystrobin Amistar 750 mg (10.3 oz) 16.1 a 29.3 abc 39.5 abc 48.3 b 238 abc Boscalid + Pyraclostrobin Cabrio 2g/L (27.3 oz) 14.9 a 32.8 abc 40.7 ab 41.3 b 240 abc

Epoxiconazole Opus 1.875 ml (24.6 fl oz) 13.6 a 17.3 c 21.8 c 22.5 c 129 d Fluoxastrobin Vigold 750 mg (10.3 oz) 15.1 a 26.8 abc 42.7 ab 43.5 b 226 abcd Kresoxim-methyl Stroby 625 mg (8.5 oz) 11.8 a 28.5 abc 47.4 ab 41.3 b 222 bcd Myclobutanil Rally 200 mg (2.7 oz) 17.5 a 28.0 abc 32.8 abc 48.8 b 228 abcd Oxycarboxin Plant Vax 3750 mg (51 oz) 18.7 a 27.5 abc 39.7 abc 37.8 b 187 cd Propiconazole Tilt 2.5 ml (32.8 fl oz) 20.3 a 24.0 bc 30.1 bc 34.8 b 180 cd Pyraclostrobin Headline 1 ml (13.1 fl oz) 13.1 a 31.8 abc 33.1 abc 39.0 b 220 bcd Tebuconazole Tebucur 1.5 ml (19.7 fl oz) 12.9 a 23.0 c 31.0 bc 31.3 b 178 cd Trifloxystrobin Flint 625 mg (8.5 oz) 16.7 a 24.8 bc 31.0 bc 32.5 b 214 cd Non-inoculated Control 16.8 a 43.8 a 50.4 a 75.3 a 319 ab Inoculated Control 16.5 a 42.8 ab 51.2 a 72.0 a 325 a z Means followed by same letter do not differ significantly based on Fisher’s LSD (p=0.05); shaded averages are significantly different from the untreated inoculated treatments.

Spring 2011, Tlayacapan, Morelos Disease pressure was low with the uninoculated, untreated plots starting with no disease and ending with 9.8% disease severity (Table 4). There were no differences in disease severity until the final data collection date, where all products reduced disease severity in comparison to the inoculated untreated plots. The best treatments were cyproconazole alone and combinations with strobilurins, with acibenzolar-s-methyl, chlorothalonil, chlorothalonil + propiconazole, flutolanil, and oxycarboxin + tebuconazole statistically equivalent to the best performing treatments.

Active Ingredient(s) Trade Name Product rate per liter

(per 100 gal) Disease Severity

AUDPC 4/30 5/14 5/28 Acibenzolar-s-methyl Actigard 50 GS 75 mg (1 oz) 0.0 a 0.5 a 2.0 cdef 4.0 b Azoxystrobin + Difenconazole Amistar + Score 0.75 g + 1.25 ml

(10.3 oz + 16.4 fl oz) 0.0 a 0.5 a 1.3 ef 3.3 b

Azoxystrobin + Epoxiconazole

Amistar + Opus 125

0.75 g + 1.875 ml (10.3 oz + 24.6 fl oz) 0.0 a 0.8 a 0.3 f 1.0 b

Azoxystrobin + Propiconazole Amistar + Tilt 0.75 g + 2.25 ml

(10.3 oz + 29.5 fl oz) 0.0 a 0.8 a 0.3 f 1.3 b

Clorothalonil Daconil 2787 3.75 g (51 oz) 0.0 a 0.5 a 2.8 cdef 4.5 b Clorothalonil + Propiconazole Daconil 2787+Tilt 3.75 g + 2.25 ml

(51 oz + 29.5 fl oz) 0.0 a 1.8 a 5.0 bcdef 10.0 b

Cyproconazole Alto 100 SL 1 ml (13.1 fl oz) 0.0 a 0.8 a 1.5 def 2.5 b Difenconazole Score 1.25 ml (16.4 fl oz) 0.0 a 0.8 a 6.8 bc 9.5 b Epoxiconazole Opus 125 1.875 ml (24.6 fl oz) 0.0 a 1.3 a 6.3 bcd 11.0 b Epoxiconazole + Clorothalonil

Opus 125+ Daconil 2787

1.875 ml + 3.75 g (24.6 fl oz + 51 oz) 0.0 a 0.5 a 2.8 cdef 5.3 b

Fluoxastrobin + Myclobutanil Disarm M 1.928 g (26.4 oz) 0.0 a 1.0 a 5.5 bcde 10.0 b

Flutalonil Contrast; Moncut 5 g (68 oz) 0.0 a 0.5 a 3.0 cdef 5.3 b Oxycarboxin + Tebuconazole

Plant Vax + Folicur

3.75 g + 1.5 ml (51 oz + 20 fl oz) 0.0 a 1.0 a 2.0 cdef 4.3 b

Trifloxystrobin + Oxycarboxin Flint + Plant Vax 0.625 g + 3.75 g

(8.5 oz + 51 oz) 0.0 a 0.5 a 1.0 ef 1.8 b

Non-inoculated Control 0.0 a 1.3 a 9.8 b 16.0 ab Inoculated Control 0.0 a 2.5 a 18.3 a 30.8 a z Means followed by same letter do not differ significantly based on Fisher’s LSD (p=0.05); shaded averages are significantly different from the untreated inoculated treatments.

Active Ingredient U.S.A. Trade Name for Ornamental Horticulture

Rusts for Ornamental Horticulture Plants as Listed on the Currently U.S.A. EPA Registered Label

Acibenzolar-s-methyl not registered -- Azoxystrobin Heritage Melampsora occidentalis, Phragmidium spp., Puccinia spp. Boscalid + Pyraclostrobin Pageant Puccinia spp., Uromyces spp., Coleopsporium spp.,

Gymnosporangium spp. Clorothalonil Daconil, and others Gymnosporangium spp., Pucciniastrum hydrangeae, Puccinia spp. Cyproconazole Alto 100 SL Rose Rust (Phragmidium spp.) Difenconazole Thesis (landscape uses only) Gladiolus Rust, Carnation Rust, Iris Rust, Rose Rust Epoxiconazole Not registered --

Fluoxastrobin Disarm 480SC Needle Rusts (Melampsora spp.), Phragmidium spp., Puccinia spp., Uromyces spp.

Fluoxastrobin + Myclobutanil not registered --

Flutolanil ProStar Rusts

Kresoxim-methyl Cygnus Carnation Rust (Puccinia dianthi), Chrysanthemum Rust (Puccinia horiana), Quince Rust (Gymnosporangium sp.) Rose Rust (Phragmidium sp.), Snapdragon Rust (Puccinia antirrhini)

Mycloblutanil Eagle Rusts Oxycarboxin not registered --

Propiconazole Banner Maxx Gymnosporangium juniper-virginia, Melampsora occidentalis, Phragmidium spp., Puccinia spp., Puccinastrum goeppertianum, Uromyces dianthi

Pyraclostrobin not registered -- Tebuconazole Torque Rusts including “Flower” rusts Trifloxystrobin Insignia Puccinia spp., Gymnosporangium spp., Melampsora spp.

Table 5. U.S.A. Registration Status and Labeled Rust Diseases for Tested Active Ingredients

• Triazole fungicides provided good control of gladiolus rust.

• Combinations of strobilurins and triazoles exhibited good efficacy.

• Growers in Mexico routinely use trifloxystrobin + oxycarboxin, oxycarboxin + tebuconazole, bitertanol + tebuconazole, epoxiconazole and sometimes mancozeb; this research may lead to additional compounds being registered and available in Mexico.

• Growers in the U.S.A. have several registered options for managing gladiolus rust including Pageant (boscalid + pyraclostrobin), DisArm 480SC (fluoxastrobin), ProStar (flutolanil), Eagle (myclobutanil), and Torque (tebuconazole). An option for management of gladiolus rust in the landscape is Thesis (difenconazole).

• Additional effective active ingredients where labels can be updated for Uromyces transversalis include Heritage (azoxystrobin), chlorothalonil, cyproconazole, Cygnus (kresoxim-methyl), Banner Maxx (propiconazole), Insignia (pyraclostrobin).

• Products not yet registered in the U.S.A. for application by growers but should be considered include acibenzolar-s-methyl, Thesis (difenconazole), epoxiconzaole, and oxycarboxin.

Table 4. Gladiolus rust disease severity after spring fungicide applications in commercial fields in Tlayacapan, Morelos, Mexico

z Exchange rate on 7/20/2011 of 1.0 U.S.A. Dollar = 0.085427 Mexican Pesos

United States Department of Agriculture Animal and Plant Health Inspection Service

Safeguarding American Agriculture

Table 2. Gladiolus rust disease severity after fall fungicide applications in commercial fields in Cuautla, Morelos, Mexico Table 3. Gladiolus rust disease severity after fall fungicide

applications in commercial fields in Atlixco, Puebla, Mexico

z Means followed by same letter do not differ significantly based on Fisher’s LSD (p=0.05); shaded averages are significantly different from the untreated inoculated treatments.

Table 1. Gladiolus Production in Mexico

Results

Introduction Materials & Methods Conclusions

Fig. 1.Severely infected gladiolus plant near experimental plot in Tlayacapan

Fig. 2. Experimental plots in Cuautla

This material was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS). It may not express APHIS’ views.