Proceedings of the 2007 CPM Short Course and MCPR Trade Show

Proceedings of the 2007 CPM Short Course and MCPR Trade Show December 4 6, 2007 Minneapolis Convention Center Do not Reproduce or Redistribute Without Written Consent of the Author(s)

W. R. Stevenson UW - Madison Dept of Plant Pathology

Chemical Control A critical component of many disease management programs Chemical controls complement other control measures such as regulatory (quarantines, seed tolerances), cultural (planting date, rotation, sanitation, irrigation and nutrition management), host resistance, biological and physical methods Chemicals are toxic to pathogens May be lethal to pathogen or inhibit germination, growth, multiplication of pathogen Some may affect quality of inoculum (survival, amount) Some are multiple-site toxicants, others are single site General groups include - Fungicides, bactericides, nematicides, viricides,, fumigants

Chemical Control Fungicides Common Uses Seed treatments Soil applications broadcast, in-furrow Foliar sprays, dusts, paints, systemics Post harvest sprays, dips, aerosols Use of fungicides requires thorough knowledge of host, pathogen and effect of environment Goal is to eliminate the pathogen or at least slow the rate of disease development

Examples of fungal diseases: Soybean Asian Rust

Potato Late Blight Sporangia, Zoospores, Lesions

Potato Early Blight

Alternaria solani conidia

Alternaria solani conidia germination

Conidia adversely affected by fungicide

Chemical controls have an important place in the history of plant pathology Sulfur for control of wheat rust 1000 B.C. Lime sulfur for control of grape downy mildew early 1800 s Bordeaux Mixture (copper sulfate and quicklime for control of downy mildew)(millardet 1883) 1932 Dawn of organic fungicide era

Chemical Control Effect of fungicide on disease development

Early Blight Control - Hancock, 1998 100 % Foliage Infection Untreated 80 60 40 20 0 6/29/1999 7/6/1999 7/13/1999 7/20/1999 7/27/1999 8/3/1999 8/10/1999 8/17/1999 8/24/1999 Bravo/Curzate+Bravo/ Bravo+Super Tin Bravo/ Curzate + Bravo Quadris / Curzate + Bravo Bravo/Curzate+ Manzate +Bravo Super Tin + cymoxanil BAS 500 Quadris (lo) + Bond/ Bravo

Chemical Control Key Terms Preventative prevents establishment of pathogen Curative interrupts development of established infection which is not showing symptoms Eradicant interrupts further development of established infection which is showing symptoms Antisporulant prevents or decreases inoculum production without stopping vegetative growth Systemic movement of fungicide in plant; locally systemic or translocated through plant via xylem or phloem

Major events in disease development vs. type of fungicide useful at each event

Preventative Fungicides Preventative prevents establishment of an infection (sometimes termed protectant) Provides chemical barrier to pathogen Must be present on plant before infection Not absorbed or translocated by plant Can t t stop established disease, but slow spread Complete coverage is critical Affected by environmental variables Insurance treatment

Curative Fungicide Curative interrupts development of established infection which is not showing symptoms Can cure disease Systemic (e.g. local, translaminar,, whole plant) Coverage not as critical as for preventatives Kickback activity window of opportunity Often used after disease appears Resistance in pathogen population more likely than with preventatives

Grouping Fungicides By Mode of Action Currently there are over 40 groups of fungicides classified by Mode of Action Reference: www.frac.info for complete listing Additional fungicides and Mode of Action groups added when discovered or identified

Grouping Fungicides By Mode of Action Dow AgroSciences

Table Legend Table Cell # common name Chemical Structure Major Supplier or Originator Mode of action Efficacy FRAC Group LD50 (rat) mg/kg WHO toxicity class Main Crop/Use Main Crop/Use Main Crop/Use

Fungicide Groupings FRAC Fungicide Grouping: 1-37; U, M, P Modes of Action: A - Y

Preventative Fungicide - Inorganic Elemental sulfur and copper Sulfur used since early Roman times Elemental copper rarely used because of phytotoxicity

Preventative Fungicide - Organic Multisite inhibitor Broad spectrum Used on wide array of crops Sold as Dithane, Manzate, Penncozeb

Preventative Fungicide - Organic Multisite inhibitor Broad spectrum Treatment of seed and potato seedpieces Sold as Captan

Copper Hydroxide Sold as Kocide, Champ Preventative Fungicide - Organic Multisite inhibitor Prevents spore germination Broad spectrum Organometallic/fixed copper Used on wide array of crops

Preventative Fungicide - Organic Inhibits sulfur-containing enzymes Used on many crops Sold as Bravo, Echo, Equus

Curative Fungicide - Organic Inhibition of mitosis Single site of action Used as postharvest treatment on potatoes Resistance risk is high Sold as Mertect

Curative Fungicide - Organic Inhibits RNA synthesis Primarily for control of Oomycetes Multiple sites of action Low resistance risk Used on potatoes and grapes Sold as Curzate

Curative Fungicide - Organic Inhibition of ergosterol synthesis Group 3 Single site of action Risk of resistance - Medium Useful for control of powdery mildew and rust Used on cucurbits, mint and fruit Sold as Rally and Nova

Curative Fungicide - Organic Inhibition of ergosterol synthesis Group 3 Single site of action Risk of resistance - Medium Useful for control of powdery mildew and rust Used on grasses, peanut Sold as Folicur

Curative Fungicide - Organic Inhibition of ergosterol synthesis Group 3 Single site of action Risk of resistance - Medium Useful for control of powdery mildew and rust Used on celery, sweet corn, corn, cereals Sold alone as Tilt, Stratego as mix with trifloxystrobin, Quilt as mix with azoxystrobin

Curative Fungicide - Organic Inhibition of ergosterol synthesis Group 3 Single site of action Risk of resistance - Medium Useful for control of powdery mildew and rust Sold as Domark

Strobilurin Chemistry Preventative and Curative Properties Broad spectrum Disrupts electron transport in mitochondrial cytochrome bc 1 complex Systemic Translaminar movement High risk for resistance Used on wide array of crops Sold as Quadris, Heritage, Abound

Strobilurin Chemistry Preventative and Curative Properties Broad spectrum Disrupts electron transport in mitochondrial cytochrome bc 1 complex Systemic Translaminar movement High risk for resistance Used on wide array of crops Sold as Cabrio, Headline

Critical Issues in Use of Fungicides Coverage Timing Growth phases of crop Equipment choice and calibration Weathering Weather variables Complete protection - start to finish Resistance management Safety Environment, applicator, consumer Economics of use

Fungicide Resistance Defined Inherited change in pathogen s susceptibility to a fungicide Factors: Fungicide mode of activity Multi-site e.g. mancozeb, chlorothalonil Single-site e.g. metalaxyl, members of strobilurin group Pathogen Single-cycle e.g. White mold Multi-cycle e.g. Late blight, Early blight

Late Blight Foliage Loss Reduced Yields Storage Losses Leaf Infection Tuber Decay Terminal Death Resistance To: metalaxyl mefenoxam

WI Case Example Late Blight Prior to 1992 Late blight a periodic problem 1/5 yrs US#1 genotype, A1 mating type metalaxyl sensitive Outstanding control with Ridomil MZ treatment Beginning in late 1992, appearance of new genotypes 1993 Appearance of US#8 genotype Highly aggressive, A2 mating type metalaxyl insensitive By 1996 and thereafter only US#8 genotype Effect on Control Tools Removal of metalaxyl from recommended list Addition of cymoxanil, propamocarb hydrochloride, zoxamide and dimethomorph as late blight products Heavy dependence on protectant materials old standbys

WI Case Example Late Blight The Tragedy of Late Blight 1. Loss of valuable chemistry metalaxyl/mefenoxam because of resistant pathogen genotypes 2. Some growers continued to use ineffective metalaxyl sprays heavy loss of yield and tuber quality 3. Multimillion $$ loss attributed to late blight when trusted chemicals were ineffective 4. Sudden increase in control costs $50/A control bills ballooned to >$300/A Market did not compensate for higher control costs 5. A few long established growers quit the potato business when production expenses exceeded returns

Potato Early Blight Early Blight Defoliation Reduced Yields Tuber Quality Loss Resistance To: strobilurin group

WI Case Example Early Blight Annual appearance on irrigated sands Progressive loss in foliage Affect on yield and tuber quality Traditional fungicide program included: Mancozeb, metiram, chlorothalonil, triphenyl tin hydroxide Arrival of strobilurin class of fungicides Field plot evaluation best early blight control ever seen Experimental Use Permit Quadris - 1998 - ~5,000 acres Outstanding control in split field trials Full Label (national) Quadris 1999 Thereafter - Additional strobilurin products released Amistar, Headline, Gem, Tanos (also contains cymoxanil), Reason, Evito

Comparison of Treatment Efficacy Hancock Potato Trial, 1997 Foliar Disease AUDPC Severity Early Blight 0 0.1 0.2 0.3 100 80 60 40 Untreated Bravo WS Zn 1.5 pt Quadris,.38 pt/bravo Quadris,.76 pt/bravo Early blight Late blight U Br Q.38 pt Q.76 pt 20 0 Combined 7/1 7/8 7/15 7/22 7/29 8/5 8/12 8/19 8/26 9/2 Figure 2. Spray programs in 1997 that contained azoxystrobin (Quadris) and chlorothalonil (Bravo) flattened the early blight progress curve in comparison with the untreated check and plots sprayed with chlorothalonil (Bravo) alone.

WI Case Example Early Blight Resistance risk of strobilurin group Initially considered low Resistance management wording on label Number of sprays per season, Seasonal use of products Resistance began to emerge Most cases, gradual loss of efficacy over years Other states, rapid loss of efficacy 1-2 seasons Resistance associated with site mutation Mutation at site F129L in cytochrome b gene Distribution of mutation throughout several states A 10-20 fold change in sensitivity to strobilurins Control of early blight with standard protectants Difficult with standard old time protectants

Azoxystrobin Treatment, Hancock Potato Trials, 1997-2005 Foliar Disease Severity Early Blight 100 80 60 1997 Untreated 1998 Untreated 1999 Untreated 2000 Untreated 2001 Untreated 2004 2003 2005 2002 2001 2002 Untreated 2000 40 20 0 6/22 6/28 2003 Untreated 2004 Untreated 2005 Untreated 7/4 7/10 7/16 7/22 7/28 8/3 8/9 8/15 8/21 8/27 9/2 1999 1998 1997 Figure 3A. Early blight progress in field trials conducted in 1997-2005 in plots left untreated with fungicide

Azoxystrobin Treatment, Hancock Potato Trials, 1997-2005 Foliar Disease Severity Early Blight 100 1997 Q/B 1998 Q/B 2004 2003 2005 80 1999 Q/B 2000 Q/B 2002 60 40 2001 Q/B 2002 Q/B 2003 Q/B 2001 2000 20 2004 Q/B 2005 Amistar/B 1999 1998 0 1997 6/19 6/26 7/3 7/10 7/17 7/24 7/31 8/7 8/14 8/21 8/28 9/4 Figure 3B. Early blight progress in field trials conducted in 1997-2005 in plots treated with a seasonal program containing both azoxystrobin (Quadris) (Q) and chlorothalonil (Bravo) (B)

WI Case Example Early Blight What Does Resistance To Group 11 Materials Mean For Future Management Of Early Blight? Introduction of new chemistries E.g. boscalid (Endura) Use of multiple chemistries (modes of action) in season-long control programs Reduction in number of sprays with any single mode of action, especially newer chemistries with single site activity Programs using base program of chlorothalonil or mancozeb Add 2 sprays with strobilurin mixed with protectant Add 1-2 sprays with boscalid mixed with protectant Add 1-2 sprays with triphenyltin hydroxide mixed with protectant Cost goal - <$100/A for chemical inputs in disease management program

Resistance Management Doesn t Cost It Pays Treatments Include: Total Yield cwt/a Fungicide Cost ($/A) Gross Crop Value ($) Processing Net Crop Value ($) Processing Effect on Crop Value ($ Processing) Untreated 469 0 1865 1865 0 Bravo Zn 529 65 2081 2016 151 Penncozeb 4F 521 33 1997 1964 99 Echo Zn, Headline, Endura, Dithane DF, Super Tin 622 92 2463 2371 506 $5.50 Value/Cost Table 1. Comparison of yield, fungicide cost, crop values and benefit to crop value of selected treatments Russet Burbank - 2005 field trial - Hancock WI Ag Research Station

Resistance Management Doesn t Cost It Pays Treatments Include: Total Yield cwt/a Fungicide Cost ($/A) Gross Crop Value ($) Processing Net Crop Value ($) Processing Effect on Crop Value ($ Processing) Untreated 529 0 2250 2250 0 Bravo Zn 556 62 2389 2327 77 Penncozeb 4F 576 42 2484 2442 192 Echo Zn, Headline, Endura, Dithane DF, Super Tin 618 87 2921 2834 584 $6.71 Value/Cost Table 1B. Comparison of yield, fungicide cost, crop values and benefit to crop value of selected treatments Russet Burbank - 2006 field trial - Hancock WI Ag Research Station.

How Can Growers Reduce The Risk Of Pathogen Resistance To Fungicides? Crop rotation - as long as possible Use cultivars with early blight resistance fewer inputs Use disease predictive models to time fungicide applications. Scout fields frequently Practice crop hygiene by elimination of primary inoculum sources, e.g. volunteer management, proper cull disposal and alternate host management including weeds. Monitor factors such as soil moisture and crop nutrition to avoid crop stress throughout the season. Follow label guidelines for application of all fungicides. Note label information on resistance management. Look for the Fungicide Group Code on labels and on the fungicide containers.

Resistance Risk of Fungicide Groups Group Code 1 Chemical Group Common Name Product Names Resistance Risk benzimidazoles thiabendazole Mertect High thiophanates thiophanate, thiophanate-methyl Tops, Topsin M 2 dicarboximides iprodione Rovral M to High 4 phenylamides metalaxyl mefenoxam 7 carboxamides boscalid flutolanil Ridomil Ridomil Gold, Ultra Flourish Endura Moncut, Moncoat High High Medium 9 anilino-pyrimidines pyrimethanil Scala Medium 11 strobilurins methoxy acrylate methoxy carbamate oximino acetate ozazolidine dione imidazolinone dihydro-dioxazine azoxystrobin pyraclostrobin trifloxystrobin famoxadone fenamidone fluoxastrobin Quadris, Amistar, Quadris Opti Headline Gem Tanos (contains cymoxanil) Reason Evito 12 phenylpyrroles fludioxonil Maxim L to Med High 14 aromatic hydrocarbons quintozene (PCNB) Blocker L to Med

Group Code Chemical Group Common Name Product Names Resistance Risk 15 cinnamic acids dimethomorph Forum L to Med 21 cyanoimidazole cyazofamid Ranman M to High 22 benzamides zoxamide Gavel (also contains mancozeb) L to Med 27 cyanoacetamide oximes 28 carbamates propamocarb hydrochloride cymoxanil Curzate L to Med Previcur Flex 29 2,6-dinitro-anilines fluazinam Omega Low 30 organotin compounds triphenyltin hydroxide SuperTin M M1 copper copper hydroxide Kocide, Champ Low M M3 ethylenebis dithiocarbamates (EBDC s) Resistance Risk of Fungicide Groups mancozeb maneb metiram Dithane, Manzate, Penncozeb Maneb Polyram M M4 phthalimides captan Captan Low M M5 phthalonitriles chlorothalonil Bravo, Echo, Equus Low L to Med L to Med Low Source: FRAC Website - http://www.frac.info/frac/index.htm

Useful References on the Web Greenbook source of labels and MSDS safety information on all pesticides used in U.S. http://www.greenbook.net www.greenbook.net/ CDMS Ag Chem Information Services http:// www.cdms.net/ Fungicide Resistance Action Committee (FRAC) http://www.frac.info www.frac.info/ University of Wisconsin Extension Publications http://www.uwex.edu www.uwex.edu/topics/publications/ Dow Agroscience Periodic Table of Fungicides http://learningstore.uwex.edu/plants-c16.aspx

Questions?