Effect of Evaluation Method on Efficacy of Fungicides for Managing Phytophthora

Crown and Root Rot on Peppers

Michael E. Matheron

Extension Plant Pathologist & Professor

Yuma Agricultural Centermatheron@cals.arizona.edu

Phytophthora root and crown rot on peppers

Disease cycle for Phytophthora capsici on pepper

Ristaino and Johnston

Oospore

Disease cycle for P. capsici on pepper

Oospore producessporangium

Zoospores develop in sporangium and are released

Root and crown rot

Stem lesionFruit rot

Leaf lesions

Oospore

Disease cycle for P. capsici on pepper

Oospore producessporangium

Zoospores develop in sporangium and are released

Root and crown rot

Stem lesionFruit rot

Leaf lesions

Fungicide efficacy trialsFungicide efficacy trialsInoculation of pepper plant stems with Inoculation of pepper plant stems with P. capsici P. capsici – Fungicides applied to foliage and stemsFungicides applied to foliage and stems

Soil infestation with Soil infestation with P. capsici P. capsici for plants grown in for plants grown in pots in the greenhousepots in the greenhouse– Fungicides applied by soil drenchFungicides applied by soil drench

Soil infestation with Soil infestation with P. capsici P. capsici for plants seeded for plants seeded and grown in the fieldand grown in the field– Fungicides applied to soil surface and base of plantsFungicides applied to soil surface and base of plants

Fungicides evaluatedFungicides evaluated

Product trade name (Source)

FRAC number

Active ingredient

Actigard (Syngenta) P Acibenzolar-S-methyl

Aliette (Bayer) 33 Fosetyl-Al

Forum (BASF) 40 Dimethomorph

Omega (Syngenta) 29 Fluazinam

Presidio (Valent) 43 Fluopicolide

Previcur Flex (Bayer) 28 Propamocarb

Ranman (FMC) 21 Cyazofamid

Reason (Bayer) 11 Fenamidone

Ridomil Gold (Syngenta) 4 Mefenoxam

Revus (Syngenta) 40 Mandipropamid

Protocol for pepper stem inoculationProtocol for pepper stem inoculation

4-month-old chile pepper plants used in this trial4-month-old chile pepper plants used in this trial

A circular area of epidermis removed from stem A circular area of epidermis removed from stem with a 5-mm diameter cork borer about 8 cm with a 5-mm diameter cork borer about 8 cm from potting mix surfacefrom potting mix surface

Plant foliage and stem submerged for 2 seconds Plant foliage and stem submerged for 2 seconds in a test fungicide solution, then laid horizontally in a test fungicide solution, then laid horizontally on paper towel until dryon paper towel until dry

Protocol for pepper stem inoculationProtocol for pepper stem inoculation(continued)(continued)

Plants maintained in lath house for 7 days, then Plants maintained in lath house for 7 days, then inoculated with a 5-mm-diameter agar disk inoculated with a 5-mm-diameter agar disk containing mycelium of containing mycelium of P. capsiciP. capsici, which was , which was held in place with plastic tapeheld in place with plastic tape

7 days after incubation at 7 days after incubation at 27°C, the length of resultant 27°C, the length of resultant stem cankers was recorded stem cankers was recorded

Suppression of stem canker growthSuppression of stem canker growth2009 Growth chamber trials2009 Growth chamber trials

Mean length of canker on untreated stems was 99 mm

D CD CD C C C BC BC BCA

Greenhouse studies - 2009Greenhouse studies - 2009

2-month-old pepper plants transplanted into 500 2-month-old pepper plants transplanted into 500 ml capacity pots containing potting mix infested ml capacity pots containing potting mix infested with with P. capsiciP. capsici

Tested products applied as a soil drench in Tested products applied as a soil drench in 200 ml of water per pot200 ml of water per pot

At transplanting and 14, 28 and 42 days laterAt transplanting and 14, 28 and 42 days later

Greenhouse studies - 2009Greenhouse studies - 2009(continued)(continued)

Each pot was placed in a shallow container (4 Each pot was placed in a shallow container (4 cm deep), which was filled with water dailycm deep), which was filled with water daily

Plants maintained in Plants maintained in greenhouse for about 2 months greenhouse for about 2 months

10 replicate plants per 10 replicate plants per treatment for each of 2 trialstreatment for each of 2 trials

Greenhouse studiesGreenhouse studies

The following data were collected either during or The following data were collected either during or at the end of the experimentat the end of the experiment– Duration of plant survivalDuration of plant survival– Fresh weight of plant shootsFresh weight of plant shoots– Incidence of crown rotIncidence of crown rot– Final plant mortalityFinal plant mortality

Suppression of root and crown infectionSuppression of root and crown infection2009 Greenhouse trials2009 Greenhouse trials

All nontreated plants were dead by 3 weeks after beginning of trial

Inoculated field trialsInoculated field trialsChile pepper seed planted early AprilChile pepper seed planted early April in a single in a single row on beds 106 cm apart, then thinned to a 30 row on beds 106 cm apart, then thinned to a 30 cm spacing (at UA Yuma Agricultural Center)cm spacing (at UA Yuma Agricultural Center)

Each treatment consisted of five replicate plots, Each treatment consisted of five replicate plots, each 4.6 m longeach 4.6 m long

Inoculated plots each received 150 cmInoculated plots each received 150 cm33 of of vermiculite infested with vermiculite infested with P. capsiciP. capsici, placed 5 cm , placed 5 cm deep and 8 cm from plant stems in late Junedeep and 8 cm from plant stems in late June

Tested products applied to soil and base of Tested products applied to soil and base of plants as a drench in 750 ml of water per plants as a drench in 750 ml of water per

15-plant plot when inoculated and 14, 28, and 42 15-plant plot when inoculated and 14, 28, and 42 days laterdays later

Inoculated field trialsInoculated field trialsPepper plants were generously irrigated weeklyPepper plants were generously irrigated weekly

Final disease incidence recorded in late Final disease incidence recorded in late SeptemberSeptember by counting the number of dead by counting the number of dead plants in each plotplants in each plot

Suppression of root and crown infectionSuppression of root and crown infectionSummary of three field trialsSummary of three field trials

Mean percentage of untreated plants that died per plot was 53%

Suppression of root and crown infectionSuppression of root and crown infectionSummary of three field trialsSummary of three field trials

Mean percentage of untreated plants that died per plot was 53%

Fungicide efficacy from different trialsFungicide efficacy from different trials

Possible reasons for differences in Possible reasons for differences in fungicide efficacy among experimentsfungicide efficacy among experiments

Omega is known to be a weak inhibitor of Omega is known to be a weak inhibitor of mycelial growth (stem inoculation), but very mycelial growth (stem inoculation), but very active against sporangia and zoospores (soil active against sporangia and zoospores (soil application)application)

Generally higher disease control observed in Generally higher disease control observed in greenhouse compared to field trials greenhouse compared to field trials – More thorough incorporation of fungicides within soil More thorough incorporation of fungicides within soil

in a pot compared to application to soil in the fieldin a pot compared to application to soil in the field

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