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

K. Spokas and B. Jacobson USDA-ARS Tree Apple Orchard St. Paul, MN 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 fungi (pine cone fungi), including one called 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 Strobilurin Use Across Different Commodities (US – 2006 data)

100 90 91 80 70 Pyraclostrobin 60 All Strobilurin fungicides 50 56

40 43 42 40 30 32

20 21 % of Crop Acreage Treated Acreage Cropof % 7 10 3 0

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

100

90 US 80 California 70 Minnesota 60 50 40 30

20 % Strawberry % AcreageTreated 10 0 1990 1995 2000 2005 2010

Most Recent Data 2006 Note: Data from USDA-NASS:\Chemical Use Database and Reports 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

Treated Plots (Pristine)

Control Area – No Pristine

• 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

No plot • Manual fungicide application with Post with weather station 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) 4000 (A) – 2008 – June 27 3500 2008 • 1172 GDD 3000 2500 2009 2000

(GDD) 1500 – 2009 – June 22 1000 500

• 1193 GDD CumulativeDays growingDegree 0 0 100 200 300 400 Day of Year • Differences in precipitation

60 – Not significant due to irrigation (B) 50

40

30

20

10

Cumulative(cm)Precipitation 0 0 100 200 300 400 Day of Year 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 1. Impacts on Yield

• June 26, 2008: 1172 GDD

1400 Total Strawberry Production 1200 Ripe Berries

b 1000

aab 800 1012

a 822 600 a 616

Yield (g/m_row) Yield 400

a a 200 a

0 Control Agro-K (Vigor Cal Phos with Agro-K+Pristine Boron) 64% 32% increase increase over control over control 1. Impacts on Yield

• June 22, 2009: 1193 GGD – Without fertilizer effect

Total Production Ripe Berries 1800 700 1600 600

-1 -1 1400 500 1200 1000 1197 400 800 920 300 352 600 200 260

grams (1 m row) grams (1 m row) 400 200 100 0 0 Treated Control Treated Control

• Although increased production, no statistically significant differences observed Yield Notes

• No difference observed in individual berry size – Control : 8.19 ± 2.3 g/berry – Pristine treated : 9.95 ± 3.0 g/berry

2.5

• Highest observed yield of ripe berries Pristine Treated 2.0 Control

in 2009 (887 g/1 m row) was 1.5

observed in a Pristine treated plot Count 1.0 0.5 However, results for all plots were 0.0 0 100 200 300 400 500 600 700 800 900 not statistically different g ripe berries (1 m row)-1

• Stresses the importance of looking at replicated field plots as well as multiple years of data for fungicide yield effects 2. Impacts on Soil Microbial Community

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

Control Pristine Treatment 1.00E+09

1.00E+08

1.00E+07

1.00E+06 *

1.00E+05 *

1.00E+04 logCounts Plate 1.00E+03

1.00E+02

1.00E+01

1.00E+00 Heterotrophic Anaerobic Bacteria Yeast/Molds Actinomycetes Pseudomonads Nitrogen-fixing Bacteria bacteria 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

18 16 Pristine Control Application 14 Pristine 12

10 8

6 4

CO2 Flux (g/m2/day) CO2 Flux 2 Insignificant decreases in CO flux 0 2 5/4/09 5/18/09 6/1/09 6/15/09 6/29/09 7/13/09

• Agrees with microbial sampling results Soil Gas Sampling (10 cm)

• Driving force (concentration gradient) of surface emissions

25000

Control 20000 Pristine

15000 Pristine Application 10000

CO2 (ppm)

5000

0 5/4/09 5/18/09 6/1/09 6/15/09 6/29/09 7/13/09

2200 2000 1800 1600 1400 1200 1000

N2O (ppb) 800 600 400 200 5/4/09 5/18/09 6/1/09 6/15/09 6/29/09 7/13/09 Contrast to other soil incubations

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

CO 7 2 1.2 N2O

6 1.0

-1

5 d

-1 0.8

-1

d

soil

-1

soil 0.6

4 O g

g

2

2

3 0.4

g N-N g

mg mg C-CO 0.2

2

Control Control

0.0 Control

1 Control

-0.2 0

no strob CM no strob SW no strob CM no strob SW strob 0708 CM strob 0809 CM strob 0708 CM strob 0809 CM strob 0708 SW strob 0809 SW strob 0708 SW strob 0809 SW

• Strobilurin applications decreased CO2 and N2O production 3. Pristine fate and leaching potential

µg pyraclostrobin per g soil (or straw) 2008 2009 1 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