Impacts of strobilurin fungicides on yield and soil microbial processes in Minnesota strawberry

production

K. Spokas and B. JacobsonUSDA-ARS

St. Paul, MN

Pine Tree Apple Orchard

White Bear Lake, MN

Presented at the Upper Midwest Regional Fruit & Vegetable

Growers Conference & Trade Show (Jan 21)

Background – Strobilurin fungicides

• Many of the newest and most important disease-control chemicals are in the strobilurin class of fungicides

– In 1991, 10% of global fungicide market

– Estimates currently well over 65% of global fungicide market

• Initial fungicides were isolated from wood-rotting mushroom fungi (pine cone fungi), including one called Strobilurus tenacellus

• This is the origin of the name “strobilurin” fungicides

Background (continued)

• Designated: QoI fungicides (Vincelli, 2002)

– Interfere with the electron transfer during the energy production of ATP in the fungi mitochondrial cells

– Targets the electron transfer at the site of quinol oxidation (Qo site) in the cytochrome BC1 complex

• Referred to as the QoI fungicides based on this mechanism

– Specific activity Microbial resistance issues

Why are strobilurin fungicides so effective?

1. QoI site mode of action

2. Translaminar movement

– “Across the lamina” or chemical can move through the leaf (top to bottom)

– If sprayed on the top of the leave can be found on the bottom of the leaf

3. Also can move Systemically

– Through the plant's vascular system

• leaf stem roots

• Leads to several advantages

– e.g. Compensates for incomplete spray coverage

Increasing Strobilurin (QoI) Fungicides Use

• Effective against a wide range of fungal diseases

– Water molds, downy mildews, powdery mildews, leaf spotting and blighting fungi, fruit rotters, and rusts

• Labeled for use on a variety of crops

– Berries, carrots, grapes, onions and other bulb vegetables, pome fruit, stone fruit, strawberries, tree nuts, hops, turfgrasses, and ornamentals

Strobilurin Impacts

• Several strobilurin (QoI) fungicides have been cited to cause positive plant growth and yield effects

• Testimonials of higher yielding “field trials”

– Strobilurin fungicides have been linked to changes in the hormonal balance of wheat

• Results in increased grain yield, delayed leaf senescence and reduced stomata conductance (water-conserving effects)

– Claims for other crops

• However, these positive effects are not universally observed (e.g. Vincelli and Hershman. 2009)

Still influencing the increasing popularity

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Pyraclostrobin

All Strobilurin fungicides

Strobilurin Use Across Different Commodities(US – 2006 data)

Note: Data from USDA-National Agriculture Statistics Service (NASS) Chemical Use Database located at http://www.pestmanagement.info/nass/

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California

Minnesota

Strobilurin Use in Strawberries

Note: Data from USDA-NASS:\Chemical Use Database and Reports

Most Recent Data 2006

Importance of fungi

• Fungi have many vital roles

– Soil water dynamics

• Physically bind soil particles together (hyphae)

– increase water infiltration and soil water holding capacity.

– Nutrient cycling

– Natural disease suppression

– Decomposers in the soil food web

• Particularly for hard-to-digest organic materials

– cellulose and lignin crop residues

• Any impact on fungal populations could have large ramifications on the balance of the soil system

Objectives of Current Project

1. Observe impacts on strawberry yield as a consequence of strobilurin use

2. Observe alterations in soil microbial community both in terms of structure and functionality

3. Observe fate and transport of strobilurin fungicide under irrigation

• Worst case scenario: Sandy soil + irrigation

Fungicide* evaluated

• Pristine® [BASF]#

– Contains pyraclostrobin

– Recall: Over 60% of strawberry production acres apply pyraclostrobin

– Applied at label recommended rates for strawberry*

# - Names are necessary to report factually on available data; however, the USDA neither

guarantees nor warrants the standard of the product, and the use of the name by USDA implies no

approval of the product to the exclusion of others that may also be suitable

* - This presentation reports research involving fungicides. It does not contain recommendations for

their use nor does it imply that uses discussed here have been registered. All uses of pesticides

must be registered by appropriate State and/or Federal agencies before they can be recommended

Field Plots

Control Area – No Pristine

Post with weather station

Treated Plots (Pristine)

No plot

• Triplicate plots (random placement)

• 20 ft x 4 rows of strawberry plants

• Located at edge of field to minimize impacts on management and operations at collaborator field site

• Manual fungicide application with backpack sprayer

Field Data Collected

• Continuous weather station

– Air temperature

– Precipitation

– Soil temperature (in-row and between-row)

– Soil moistures (in-row and between-row)

• Soil microbial community profiles

• Greenhouse gas fluxes (bi-weekly)

• 10 cm soil gas concentrations

1. Impacts on Strawberry Yield

• Sampling occurred close to identical growing degree days (GDD)

– 2008 – June 27

• 1172 GDD

– 2009 – June 22

• 1193 GDD

• Differences in precipitation

– Not significant due to irrigation

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Strawberry Sampling

• Sampling

• All berries picked in 1 m (3 ft) long row sections

• 4 sections per plot (randomly selected from 2 middle rows)

• Excluded 5 ft from plot edge

• Separated out ripe berries (red) within 1 day of picking

• Total berries counted and weighed

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Control Agro-K (Vigor Cal Phos with Boron)

Agro-K+Pristine

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Total Strawberry Production

Ripe Berries

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1. Impacts on Yield

• June 26, 2008: 1172 GDD

32% increase

over control

64% increase

over control

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1012

1. Impacts on Yield

• June 22, 2009: 1193 GGD

– Without fertilizer effect

Treated Control

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Treated Control

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700Ripe Berries

• Although increased production, no statisticallysignificant differences observed

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• No difference observed in individual berry size

– Control : 8.19 ± 2.3 g/berry

– Pristine treated : 9.95 ± 3.0 g/berry

• Highest observed yield of ripe berries

in 2009 (887 g/1 m row) was

observed in a Pristine treated plot

However, results for all plots were

not statistically different

• Stresses the importance of looking at replicated field plotsas well as multiple years of data for fungicide yield effects

Yield Notes

g ripe berries (1 m row)-1

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Control

2. Impacts on Soil Microbial Community

• Some alterations in the field were seen immediately following Pristine application (surface soil)

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Heterotrophic Bacteria

Anaerobic Bacteria Yeast/Molds Actinomycetes Pseudomonads Nitrogen-f ixing bacteria

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ounts

Control Pristine Treatment

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2. Impacts on Soil Microbial Community

Summary –

Differences between field and laboratory testing:

Fungicide decreases yeasts/molds (fungi):

75% reduction in laboratory incubations

37% reduction in field plots

Pseudomonads (aerobic gram-negative bacteria)

240% increase in field sampling

No significant increases seen in laboratory incubations

Heterotrophic bacteria

No significant differences were observed in the field

Laboratory incubations increased heterotrophic bacteria nearly 2-fold (90% increase)

Possible explanation Field behavior of fungicide

2. Greenhouse Gas Fluxes(functionality)

• No differences observed for nitrous oxide (N2O), carbon dioxide (CO2) or methane (CH4) surface flux

5/4/09 5/18/09 6/1/09 6/15/09 6/29/09 7/13/09

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Pristine Application

Insignificant decreases in CO2 flux

• Agrees with microbial sampling results

Soil Gas Sampling (10 cm)

• Driving force (concentration gradient) of surface emissions

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Pristine Application

Contrast to other soil incubations

• Soils with 10+ year history of strobilurin application have also been evaluated in the laboratory

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• Strobilurin applications decreased CO2 and N2O production

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3. Pristine fate and leaching potential

µg pyraclostrobin per g soil (or straw)

2008 20091 day after application 3 days after application

Surface Straw Mulch 1.5 1.0

0-5 cm <1.0 <1.0

5-10 cm <1.0 <1.0

10-15 cm <1.0 <1.0

15-20 cm <1.0 <1.0

20-25 cm <1.0 <1.0

25-50 cm <1.0 <1.0

Fungicide only detected in straw mulch immediately after application

Strobilurin fate and leaching potential

µg pyraclostrobin per g soil (or straw)

2008 2009>7 days after application >7 days after application

Surface Straw Mulch <1.0 <1.0

0-5 cm <1.0 <1.0

5-10 cm <1.0 <1.0

10-15 cm <1.0 <1.0

15-20 cm <1.0 <1.0

20-25 cm <1.0 <1.0

25-50 cm <1.0 <1.0

After 1 week and following No detection of fungicide

in soil or mulch

3. Pristine Leaching

• No leaching observed in the 2 years of field sampling

• Fungicide was not detected in the soil beneath the straw mulch

– Could explain differences between impacts seen in laboratory soil incubations and field observations

– Also could explain observed differences between soils from fields with long history (10+ years) of strobilurin use (no mulch present) and soil from current strawberry production

– Could straw mulch protect the soil from fungicide impacts?

Summary

• Strobilurin use is increasing at exponential rates

– Particularly high percent use in fruit and vegetable production

• No statistically significant yield increases observed in the first two years of project as a result of fungicide applications

• Only significant observation: fertilizer + fungicide vs. control(2008)

• 65% increase in total production

• All other yields of fungicide to control were not significantly different due to natural variability in the production rates across the field

– Differences did not exceed those that were expected by chance

Summary

• Minor alteration seen in field soil microbial community structure

– Differences did disappear with time

– Results were different than laboratory incubations

• No fungicide in the field soil

• No leaching of fungicide was detected into the soil system

– Strobilurin fungicide only detected in straw mulch immediately after application & dissipated quickly (7 days)

– Could be one of the reasons for lack of significant microbial impacts

• Current plan is for one more year of monitoring

Acknowledgements

• Bill Jacobson and the entire staff at Pine Tree Apple Orchards for their assistance

• Martin du Saire, Tia Phan, Lianne Endo, Lindsey Watson and Matt Montgomery for their assistance with laboratory gas analyses and field sampling

• Brian Barber for his assistance in running the LC-MS analyses of the soil and straw extractions