Potted strawberry plants color-coded for different treatments.  Photo by Surendra Dara

Charcoal rot, caused by Macrophomina phaseolina, is one of the important fungal diseases of strawberry in California.  Macrophomina phaseolina is a soilborne fungus and has a wide host range, including alfalfa, cabbage, corn, pepper, and potato, some of which are cultivated in the strawberry production areas in California.  The fungus infects the vascular system of the plant roots, obstructing the nutrient and water supply and ultimately resulting in stunted growth, wilting, and death of the plant.  The fungus survives in the soil and infected plant debris as microsclerotia (resting structures made of hyphal bodies) and can persist for up to three years.  Microslerotia germinate and penetrate the root system to initiate infection.  Plants are more vulnerable to fungal infection when they are experiencing environmental (extreme weather or drought conditions) and physiological (heavy fruit bearing) stress.

Soil fumigation is the primary management option for addressing charcoal rot in strawberry.  Crop rotation with broccoli can also reduce the risk of charcoal rot due to glucosinolates and isothiocyanates in broccoli crop residue that have fungicidal properties.  Beneficial microorganisms such as Bacillus spp. and Trichoderma spp. are also considered, especially in organic strawberries, to antagonize M. phaseolina and other soilborne pathogens and provide some protection.  The role of beneficial microbes in disease management or improving crop growth and health is gaining popularity in the recent years with the commercial availability of biofungicide, biostimulant, and soil amendment products.  In a couple of recent strawberry field studies in Santa Maria, some of the beneficial microbial products improved fruit yield or crop health.  These treatments can be administered by inoculating the transplants prior to planting, immediately after planting or periodically applying to the plants and or the soil.  Adding beneficial microbes can help improve the soil microbiome especially after chemical or bio-fumigation and anaerobic soil disinfestation. 

Similar to the benefits of traditionally used bacteria (e.g., Bacillus spp. and Pseudomonas spp.) and fungi (e.g., Glomus spp. and Trichoderma spp.), studies with entomopathogenic fungi such as Beauveria bassiana, Isaria fumosorosea, and Metarhizium spp. also demonstrated their role in improving water and nutrient absorption or antagonizing plant pathogens.  The advantage of entomopathogenic fungi is that they are already used for arthropod pest management in multiple crops, including strawberry; now, there are the additional benefits of promoting crop growth and antagonizing plant pathogens.  In light of some promising recent studies exploring these roles, a study was conducted using potted strawberry plants to evaluate the efficacy of two California isolates of Beauveria bassiana and Metarhizium anisopliae s.l. and their application strategies against M. phaseolina.

Methodology

About 6 week old strawberry plants (cultivar Albion) from a strawberry field at the Shafter Research Station were transplanted into 1.6-gallon pots with Miracle-Gro All Purpose Garden Soil (0.09-0.05-0.07 N-P-K) and maintained in an outdoor environment.  They were regularly watered, and their health was monitored for about 5 months prior to the commencement of the study.  Conidial suspensions of the California isolates of B. bassiana and M. anisopliae s.l. were applied one week before, after, or at the time of applying microsclerotia of M. phaseolina to the potting mix.  The following treatments were evaluated in the study:

1. Untreated control
2. Soil inoculated with M. phaseolina
3. Soil inoculated with  B. bassiana 1 week prior to M. phaseolina inoculation
4. Soil inoculated with  M. anisopliae s.l. 1 week prior to M. phaseolina inoculation
5. Soil inoculated with  B. bassiana at the time of M. phaseolina inoculation
6. Soil inoculated with  M. anisopliae s.l. at the time of M. phaseolina inoculation
7. Soil inoculated with  B. bassiana 1 week after to M. phaseolina inoculation
8. Soil inoculated with  M. anisopliae s.l. 1 week after to M. phaseolina inoculation

Entomopathogenic fungi were applied as 1X10¹⁰ viable conidia in 100 ml of 0.01% Dyne-Amic (surfactant) solution distributed around the plant base.  To apply M. phaseolina, 5 grams of infested cornmeal-sand inoculum containing 2,500 CFU/gram was added to four 5 cm deep holes around the base of the plant.  Each treatment had six pots each planted with a single strawberry plant representing a replication.  Treatments were randomly arranged within each replication.  The study was repeated once a few days after the initiation of the first experiment.

Plant health was monitored starting from the first week after the M. phaseolina inoculation and continued for seven weeks.  Plant health was rated on a scale of 0 to 5 where 0=dead and 5=very healthy and the rest of the ratings in between depending on the extent of wilting.  Data from both experiments were combined and analyzed by ANOVA using Statistix software and significant means were separated using LSD test.  The influence of entomopathogenic fungal treatments applied at different times as well as the combined effect of different applications within each fungus were compared for seven weeks.  Ratings for some plants that were scorched from hot summer temperatures and died abruptly were removed from the analyses.

Results

Untreated control plants maintained good health throughout the observation period varying between the rating of 4.3 and 4.9.  In general, plant health declined considerably from the 5^th week after M. phaseolina inoculation.  Plant health appeared to be slightly better in plants treated with entomopathogenic fungi, but there was no statistically significant difference in any except one instance.  Plants treated with M. anisopliae one week prior to the application of M. phaseolina had a rating of 3.0 compared to 1.6 rating of plants inoculated with M. phaseolina alone.  

Plant health rating each week after inoculating with Macrophomina phaseolina.  Bars followed by the same letter within each week are not statistically different.

When data from different treatments for each entomopathogenic fungus were compared, both B. bassiana and M. anisopliae s.l. appeared to reduce the wilting, but the plant health rating was not significantly different from the M. phaseolina treatment alone.

This is the first report of the impact of entomopathogenic fungi on M. phaseolina with some promise.  Additional studies under more uniform environmental conditions and with more treatment options would shed more light on this approach of using entomopathogenic fungi against M. phaseolina.  The current study evaluated single application of the entomopathogenic fungi and we plan to conduct additional studies with multiple applications.

Acknowledgements: We thank Dr. Kelly Ivors (previously at Cal Poly San Luis Obispo) for the pathogen inoculum and Dr. Stefan Jaronski, USDA-ARS, Sidney, MT for multiplying the entomopathogenic fungal inocula.

References

Dara, S. K. and D. Peck.  2017. Evaluating beneficial microbe-based products for their impact on strawberry plant growth, health, and fruit yield.  UC ANR eJournal Strawberries and Vegetables. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=25122

Dara, S. K. and D. Peck.  2018.  Evaluation of additive, soil amendment, and biostimulant products in Santa Maria strawberry.  CAPCA Adviser, 21(5): 44-50.

Dara, S. K., S.S.R. Dara, and S. S. Dara.  2017.  Impact of entomopathogenic fungi on the growth, development, and health of cabbage growing under water stress.  Amer. J. Plant Sci. 8: 1224-1233.  http://file.scirp.org/pdf/AJPS_2017051714172937.pdf

Dara, S. K., S. S. Dara, S.S.R. Dara, and T. Anderson.  2016.  First report of three entomopathogenic fungi offering protection against the plant pathogen, Fusarium oxysporum f.sp. vasinfectum.  UC ANR eJournal Strawberries and Vegetables. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22199

Koike, S. T., G. T. Browne, and T. R. Gordon.  2013.  UC IPM pest management guidelines: Strawberry diseases.  UC ANR Publication 3468. http://ipm.ucanr.edu/PMG/r734101511.html

Partridge, D. 2003. Macrophomina phaseolina.  PP728 Pathogen Profiles, Department of Plant Pathology, North Carolina State University.  https://projects.ncsu.edu/cals/course/pp728/Macrophomina/macrophominia_phaseolinia.HTM

Vasebi, Y., N. Safaie, and A. Alizadeh.  2013.  Biological control of soybean charcoal root rot disease using bacterial and fungal antagonists in vitro and greenhouse condition.  J. Crop Prot. 2(2): 139-150.

http://ucanr.edu/articlefeedback 

Experimental plots in mid January, 2018. Photo by Surendra Dara

In a continuous effort to explore the potential of additive, soil amendment, biostimulant, and other products, a new study was conducted in a conventional strawberry field at the Manzanita Berry Farms in Santa Maria.  The following treatments were administered at different times, from planting till the end of production season, as requested by the manufacturer.

1. Untreated control: Other than the soil incorporated fertilizers during the field preparation, no other nutrient inputs were added during the study.
2. Grower standard: Transplants were dipped in Switch 62.5WG (cyprodinil+fludioxonil, at 5 oz/100 gal) before planting and a proprietary nutrient regimen that included administration of a humic acid-based product was followed.
3. Innovak Global regimen: Nutrisorb-L (a blend of polyhydroxy carboxylic acids) at 28 fl oz/ac, starting 2 wk after planting and every 3 wk thereafter through drip.  Packhard (carboxylic acids with calcium and boron) at 28 fl oz/ac, starting at the first fruit set (early January) and every 2 wk thereafter as a foliar spray. 
4. TerraVesco regimen: A microbe-rich Vermi-extract (worm extract) at 10% vol/vol as a transplant dip for 3 hours, followed by application through drip at 7.5 gal/ac after planting, and again in December, 2017 and January, 2018.
5. Fertum regimen: Transplant dip in 1% vol/vol of Germinal Plus (a product from marine algae), followed by drip applications of Booster (a biostimulant and a natural organic fertilizer made from seaweed) at 0.5 gal/ac in late November and late December, 201; Silicium PK (a biostimulant and a natural organic fertilizer based on silicon enriched with phosphorus, potassium and seaweed extracts) at 0.5 gal/ac late December, 2017 and once a month starting from mid February to early July, 2018; and Foliar (a biostimulant and a natural organic fertilizer from marine algae) at 0.5 gal/ac in mid and late January.
6. Shemin Garden regimen: EcoSil (a silica fertilizer) at 800 ml/ac once a month starting from early December, 2017 to May, 2018 through drip, and at 200 ml/ac in early May and June, 2018 as a foliar spray; ComCat (based on a plant extract) at 20 gr/ac and EcoFlora (a consortium of Azotobacter spp., Bacillus spp., Paenibacillus spp., Pseudomonas sp., Trichoderma spp., and Streptomyces spp.) at 12 oz/ac one week after EcoSil through drip until May, 2018 and ComCat at 10 gr/ac and EcoFlora at 12 oz/ac as a foliar spray in May and June, 2018.
7. GrowCentia regimen-low: Yeti containing 1% bacterial culture (of Pseudomonas putida, Citrobacter freundii, Comamonas testosterone, and Enterobacter cloacae) and 2% alfalfa extract applied at 0.6 ml/gal through drip for 90 min weekly from the first drip application.
8. GrowCentia regimen-high: Yeti at 1 ml/gal through drip for 90 min weekly from the first drip application.
9. NanoChem regimen: EX10, a biodegradable fertilizer additive containing thermal polyaspartate at 1 qrt/ac through first drip after planting with follow up applications in early January (first bloom), mid February, and mid May, 2018.  The active ingredient binds with cations such as ammonium, calcium, copper, iron, magnesium, manganese, potassium, and zinc and improves their availability for the plant.
10. BiOWiSH regimen 1: Formula 1 at 1.33 oz/gal for transplant dip followed by 3.53 oz/ac through drip starting 2 wk after planting and every 4-5 wk thereafter.
11. BiOWiSH regimen 2: Formula 1 at 1.33 oz/gal for transplant dip followed by 3.53 oz/ac as a foliar srpay starting 2 wk after planting and every 4-5 wk thereafter.
12. BiOWiSH regimen 3: Formula 1 at 1.33 oz/gal for transplant dip followed by 3.53 oz/ac through drip starting 2 wk after planting alternated with a foliar spray every 4-5 wk.
13. BiOWiSH regimen 4: Formula 1 at 1.33 oz/gal for transplant dip followed by BiOWiSH Crop 16-40-0, a microbial consortium (Bacillus amyloliquefaciens, B. lichenoformis, B. pumilus, and B. subtilis)at 3.53 oz/ac through drip starting 2 wk after planting and every 4-5 wk thereafter.

Each treatment contained a 165' long 5.7' wide bed and replicated four times in a randomized complete block design.  A 15' long plot in the center of the bed was marked and netted for collecting yield and some other parameters that were compared.  Strawberry cultivar BG 6-30214 was planted on 7 November, 2017.  Other than the untreated control, all other products were administered on top of the grower standard fertility program.  However, only the grower standard transplants were dipped in Switch 62.5WG before planting. 

Various parameters were measured during the vegetative growth and fruit production periods to evaluate the impact of the treatments on crop growth, health, and yield.  Data were analyzed using ANOVA and LSD test was used to separate significant means.

Transplant treatment (above) and drip application (below).  Photos by Tamas Zold

Tamas Zold taking canopy measurements.  Photo by Surendra Dara

Canopy growth: Canopy growth was observed on 11 December, 2017, 7 and 30 January, and 8 February, 2018 by measuring the size of the canopy along and across the length of the bed from 20 random plants per bed and calculating the area.  Canopy size significantly (P = 0.0261) different among the treatments only on the last observation date where plants treated with EX10 and the GrowCentia product at the low concentration were larger than those in the grower standard.

Electrical conductivity and temperature of soil: From two random location on each bed, electrical conductivity (EC in dS/m) and temperature (^oC) were measured about 3 inches deep from the surface on 12 and 25 January, 7 February, 19 March, 18 April, and 29 May, 2018.  Only soil temperature on 25 January significantly (P = 0.0007) varied among treatments where the difference between the highest (untreated control) and the lowest (Vermi-extract) values was 0.8^oC.

Dead plants: The number of dead plants represents empty spots in the bed due to the death of transplants.  There were no obvious signs of disease or a particular stress factor associated with those plants except that they were randomly distributed within each bed and throughout the field.  When counted on 18 April, 2018, BiOWiSH regimen 4, Fertum regimen, GrowCentia product at the high rate, and Innovak Global regimen had 

Areas where transplants did not establish.  Photo by Surendra Dara

Fruit diseases: Fruit harvested on 12 March, 3 and 13 April, and 17 May, 2018 from each marked plot was incubated at room temperature in dark in plastic containers and the fungal growth was rated 3 and 5 days after harvest (DAH) using a scale of 0 to 4 where 0=no fungal growth, 1=1-25%, 2=26-50%, 3=51-75%, and 4=76-100% fungal growth. Botrytis fruit rot or grey mold was predominant during the first two observation dates and the growth of other fungi (possibly Rhizopus spp.) was also seen during the last two dates.  In general, fruit disease occurred at low levels throughout the observation period with

Sugar content in fruit: Sugar content was measured from two harvest-ready berries per bed on 17 May, 2018 using a handheld refractometer.  Sugar content varied from 8.06 ^oBx (Innovak Global regimen) to 9.53 ^oBx (grower standard).

Fruit firmness: Fruit firmness was measured from eight randomly collected harvest-ready berries from each bed on 28 June, 2018.  Firmness varied from 0.82 kgf (Fertum and Shemin Garden regimens) to 0.98 kgf (untreated control).

Fruit yield:Strawberries were harvested from 6 February to 22 June, 2018 on 36 dates.  When compared to the grower standard, the marketable berry yield was 16.2, 15.1, 13.7, and 13% higher in Fertum regimen, EX10 treatment, Innovak Global regimen, and BiOWiSH regimen 4, respectively.  The marketable berry yield was 9.8, 9, 7.5, and 6.8% higher in those respective treatments over the yield from untreated control.  

When data were analyzed without the untreated control, there was a significant difference (P = 0.0279) among the treatments where treatment 5 had significantly higher marketable yield than the grower standard and treatments 3, 8, and 11.  Percentage difference from grower standard yield was also significantly different (P = 0.0301) among treatments where the Fertum regimen had the highest increase of 16.25.

Seasonal marketable yields (above) and percentage difference compared to grower standard (below) when untreated control data were excluded from the analyses.

There was a significant difference (P = 0.0141) among treatments only in the number of marketable berries.  There were more than 1700 in Innovak Global regimen, EX10 treatment, and BiOWiSH regimen 4 while grower standard had 1485, Vermi-extract had 1563, and the rest of the treatments had marketable berries in 1600s.  

 

The average fruit weight was a little over 33 grams in the grower standard and the Fertum regimen whereas the weight varied between 31.9 and 32.7 grams in the rest of the treatments.  

 

It took 23 harvest dates in three months (from February to April, 2018) to obtain the first third of the total seasonal yield while the remaining two-thirds were obtained from seven harvest dates in May and six dates in June.  Marketable fruit yield was higher than the grower standard in all treatments and higher than the untreated control in most treatments. 

In general, fruit yields were higher and the pest and disease pressure was lower than usual during the study period.  Aleo, a garlic oil based fungicide, at lower label rates was periodically used for disease management and bug vacuums were operated a few times against the western tarnished plant bug as a standard across all treatments.

This study evaluated some treatment regimens as recommended by the collaborating manufacturers and some of them appear to have a potential for use in strawberry production.  These results help the manufacturers fine tune their recommendations for achieving better yields through additional studies.

Acknowledgments: We thank the planting and harvest crew at Manzanita Berry Farms for their help with the crop production aspects, Chris Martinez, Tamas Zold, and Maria Murrietta for their technical assistance, Sumanth Dara for statistical analysis, and the support of the industry collaborators who funded the study.

http://ucanr.edu/articlefeedback

The western tarnished plant bug (or lygus bug) and different species of spider mites are major arthropod pests in California strawberries. While predatory mite releases are very popular for controlling spider mites in both organic and conventional fields, a significant amount of chemical pesticides are used for arthropod pest management in conventional fields. Nearly 280,000 pounds of active ingredient of at least 30 chemical and botanical pesticides were used in 2016 in California strawberries (USDA-NASS, 2016; CDPR, 2017) and malathion, bifenazate, naled, acequinocyl, and fenpropathrin were the most common of about 79,000 pounds of chemical pesticides. A uniform and thorough coverage of pesticide sprays is essential for effective pest management and also for reducing excessive pesticide use that could lead to resistance and environmental health issues (Shi et al., 2013). Evaluation of pesticide spray applications and their performance will help improve current pest management strategies in strawberry as they did in other crops (Nansen et al., 2011; Nansen et al., 2015).

Several factors such as the tractor speed, spray nozzles, spray volume, boom height, adjuvants, pressure, canopy characters, micro and macroclimatic conditions influence the spray coverage. A better understanding of these factors will help improve the pesticide use and efficacy, optimize the cost, and reduce pesticide drift and other associated risks (Nansen and Ridsdill-Smith, 2013).

A study was conducted during 2016 and 2017 to evaluate multiple spray configurations under varying weather conditions where more than 4000 data points were collected. Data for only two spray configurations, using Albuz ATR 80 Lilac and Albuz ATR 80 Green nozzles, are shown here.

Collecting the spray cards for evaluating the spray coverage (above).  Photo by Elvira de Lange.

Water-sensible spray card in the strawberry canopy (above) and determining the spray coverage with the help of SnapCard app (below).  Photos by Elvira de Lange.

Configuration 1: Albuz ATR 80 Lilac nozzles were used in 144 experimental applications delivering 32-80 gallons of spray volume per acre. Water-sensitive spray cards (TeeJet, Wheaton, IL) were clipped to the petioles of strawberry leaves in horizontal and vertical orientation (1 card per application for each orientation).  They were placed in the strawberry canopy prior to spray applications and the coverage was determined based on the pattern on the cards using the SnapCard smartphone application. Data suggested that spray volume does not always translate into a good spray coverage (Fig. 1). There was a wide variation in the coverage that ranged from 0-55% at 33 gpa and 5-80% at 80 gpa suggesting the influence of other factors. Taking the operational and weather conditions into account, a multiple linear regression analysis was conducted to measure the relationship between predicted and observed spray coverage which appeared to have a linear correlation (Adjusted R2=0.27; F+52.6; P < 0.001) (Fig. 2). Wind speed, wind gust, ambient temperature, pressure, and tractor speed were used as explanatory variables in this analysis. Based on this regression model, four possible scenarios were developed with predicted spray coverage values (Table 1). A 2 mph increase in the wind speed from 6 mph to 8 mph could reduce the spray coverage from 61 to 45% when the tractor runs at 1 mph or from 30 to 13% when the tractor runs at 2 mph.

Fig. 1. Spray coverage related to the volume using the Albuz ATR 80 Lilac nozzle.

Fig. 2. Modeling spray coverage under different conditions using the Albuz ATR 80 Lilac nozzle.

Configuration 2: Albuz ATR 80 Green nozzles were used in 276 experimental applications delivering 180-440 gallons of volume per acre. Since the droplet size from the Green nozzle is much larger than that from the Lilac nozzle, a better coverage is expected with the presumption of lesser sensitivity to environmental and operating conditions. However, data from the spray cards indicated a poor relationship between the spray volume and coverage under this configuration as well (Fig. 3).  For example, both 200 and 350 gpa had a similar spray coverage. Multiple linear regression analysis, using strawberry canopy characteristics (plant height and width, dry weight, and canopy coverage), operating and weather conditions as explanatory variables, showed a significant linear correlation  (Adjusted R2=0.45; F=199.5; P < 0.001) between observed and predicted spray coverages (Fig. 4). A prediction model under this configuration showed nearly 20% decline in spray coverage when the tractor speed increased from 1 to 2 mph (Table 2). Wind speed appeared to have a minimal impact, probably due to the droplet size.

Fig. 3. Spray coverage related to the volume using the Albuz ATR 80 Green nozzle.

Fig. 4. Modeling spray coverage under different conditions using the Albuz ATR 80 Lilac nozzle.

This study demonstrates the importance of weather and operating conditions on spray coverage.  Additional data will be collected in 2018 to expand our understanding of the factors that influence spray coverage. These studies will be useful to determine appropriate operating conditions such as the spray volume, tractor speed, and types of nozzles and identify weather conditions that are ideal to achieve good coverage. A free smartphone application is under development for the growers and PCAs to input weather and operating conditions to predict the spray coverage. This information will ultimately improve the pest control efficacy and contribute to sustainable pest management practices.

Acknowledgments: We thank the financial support of the California Strawberry Commission and the collaboration of several growers.  We also thank the technical assistance of Daniel Olivier, Marianna Castiaux, and Ariel Zajdband, California Strawberry Commission and Robert Starnes, Jessie Liu, Laurie Casebier, Haleh Khodaverdi, and Isaac Corral, UC Davis.

References

CDPR.  2017.  Summary of pesticide use report data 2016:  California Department of Pesticide Regulation, p. 909.

Nansen C, Ferguson JC, Moore J, Groves L, Emery R, Garel N and Hewitt A.  2015.  Optimizing pesticide spray coverage using a novel web and smartphone tool, SnapCard. Agronomy for Sustainable Development: 1-11. DOI: 10.1007/s13593-015-0309-y.

Nansen C & Ridsdill-Smith TJ (2013) The performance of insecticides – a critical review: Insecticides (ed. by S Trdan) InTech Europe, Croatia, pp. 195-232.

Nansen C, Vaughn K, Xue Y, Rush C, Workneh F, Goolsby J, Troxclair N, Anciso J, Gregory A, Holman D, Hammond A, Mirkov E, Tantravahi P and Martini X (2011) A decision-support tool to predict spray deposition of insecticides in commercial potato fields and its implications for their performance. Journal of Economic Entomology 104: 1138-1145. DOI: 10.1603/EC10452.

Shi M, Collins PJ, Ridsdill-Smith TJ, Emery RN and Renton M.  2013. Dosage consistency is the key factor in avoiding evolution of resistance to phosphine and population increase in stored-grain pests. Pest Management Science 69: 1049–1060. DOI: 10.1002/ps.3457.

USDA_NASS.  2016. Quick stats.

http://ucanr.edu/articlefeedback

Six-month old strawberry field.

Under the soil is a complex and dynamic world of moisture, pH, salinity, nutrients, microorganisms, and plant roots along with pests, pathogens, weeds and more.  A good balance of essential nutrients, moisture, and beneficial microorganisms provides optimal plant growth and yield.  These factors also influence natural plant defenses and help withstand stress caused by biotic and abiotic factors. 

Several beneficial microbe-based products are commercially available to promote plant growth and improve health, yield potential and quality.  Some of them improve nutrient and water absorption while others provide protection against plant pathogens or improve plant defense mechanism.  In addition to the macronutrients such as nitrogen, phosphorus, and potassium, several micronutrients are critical for optimal growth and yield potential.  Some of the micronutrient products are also useful in promoting beneficial microbes.  Understanding the plant-microbe-nutrient interactions and how different products help crop production are helpful for making appropriate decisions.

Mycorrhizae (fungi of roots) establish a symbiotic relationship with plants and serve as an extended network of the root system. They facilitate improved uptake of moisture and nutrients resulting in better plant growth and yield (Amerian and Stewart, 2001; Wu and Zou, 2009; Bolandnazar et al., 2007; Nedorost et al., 2014).  Mycorrhizae can also help absorb certain nutrients more efficiently than plants can and make them more readily available for the plant.  With increased moisture and nutrient absorption, plants can become more drought-tolerant.  Mycorrhizae also help plants to withstand saline conditions and protect from plant pathogens.  A healthy root system can fight soil diseases and weed invasion.  Additionally, mycorrhizae increase organic matter content and improve soil structure.

Considering an increasing need for fumigation alternatives to address soilborne pathogens in strawberry, mycorrhizae and other beneficial microbes could be potential tools in maintaining plant health.  Additionally, recent studies suggest that entomopathogenic fungi such as Beauveria bassiana, Metarhizium brunneum, and Isaria fumosorosea form mycorrhiza-like and endophytic relationships with various species of plants and could help with plant growth and health (Behie and Bidochka, 2014; Dara et al., 2016).  These fungi are currently used for pest management, but their interaction with plants is a new area of research.  Understanding this interaction will potentially expand the use of the biopesticides based on these fungi for improving plant growth and health.  A study was conducted at Manzanita Berry Farms, Santa Maria in fall-planted strawberry crop during the 2014-2015 production season to evaluate the impact of beneficial microbes on strawberry growth, health, mite infestations, powdery mildew, botrytis fruit rot, and yield.

Methodology:

List of treatments, their application rates and frequencies:

1. Untreated control: Received no supplemental treatments other than standard grower practices.
2. HealthySoil: NPK (0.1-0.1-0.1).
3. BotaniGard ES: Entomopathogenic fungus Beauveria bassiana strain GHA.  Rate - 1 qrt in 50 gal for a 30 min transplant dip and 1 qrt/ac every 15 days until January and once a month thereafter until April, 2015.
4. Met52: Entomopathogenic fungus Metarhizium brunneum strain F52.  Rate – 16 fl oz in 50 gal for a 30 min transplant dip and 16 fl oz/ac every 15 days until January and once a month thereafter until April, 2015.
5. NoFly: Entomopathogenic fungus Isaria fumosorosea strain FE9901.  Rate – 11.55 oz in 50 gal for a 30 min transplant dip and 11.55 oz/ac every 15 days until January and once a month thereafter until April, 2015.
6. Actinovate AG: Beneficial soilborne bacterium Streptomyces lydicus WYEC 108.  Rate – 6 oz in 50 gal for a 30 mintransplant dip and 6 oz/ac every month.
7. TerraClean 5.0: Hydrogen dioxide and peroxyacetic acid.  Rate – 1:256 dilution for a 1 min root dip followed by 2 gal/ac 10 days after planting and then 2 and 1 gal/ac alternated every 15 days until April, 2015.
8. TerraGrow: Humic acids, amino acids, sea kelp, glucose based carriers, bacteria – Bacillus licheniformis, B. subtilis, B. pumilus, B. amyloliquefaciens, and B. magaterium, and mycorrhizae – Trichoderma harzianum and T. reesei.  Rate – 1.13 g in 10 gal for a 1 min root dip followed by 1.5 lb/ac 10 days after planting and once every month until April, 2015.
9. TerraCelan and TerraGrow: Same as individual treatments at the time of planting, but TerraClean at 2 gal/ac and TerraGrow at 1.5 lb/ac 10 days after planting followed by monthly treatments until April, 2015.
10. O-MEGA: NPK (0.2-1.0-0.5), bacteria – Azotobacter chroococcum, Azospirillum lipoferum, Lactobacillus acidophilus, Pseudomonas fluorescens, Cellulomonas cellulans and the fungus Aspergillus niger.  Rate – 20 ml in 1 gal sprinkled on transplants 30 min before planting followed by 1 qrt/ac every week rest of the season.

Strawberry transplants (variety BG-6.3024) were treated at the time of planting on 6 November, 2014 and treatments are also administered periodically through the drip irrigation system following the abovementioned schedule.  Each treatment had two 330' long beds each with four rows of plants.  Treatments were randomly arranged in two blocks and two sampling plots (20' long) were established within each bed in a block.  The impact of the treatments on plant growth (canopy size), health, spider mite populations, botrytis and powdery mildew severity, and yield were monitored periodically.  Plant growth was determined by measuring the canopy size.  Plant health was rated on a scale of 0 to 5 where 0=dead, 1=weak, 2=moderate low, 3=moderate high, 4=good, and 5=very good.  Powdery mildew severity was determined by observing leaf samples under microscope and rating the severity on a scale of 0 to 4 where 0=no infection, 1=1-25%, 2=26-50%, 3=51-75%, and 4=76-100% of leaf area with powdery mildew.  Twenty plants or leaf samples per plot were used for these observations.  To monitor botrytis fruit rot, a box of fruits from each plot were held at room temperature and disease was rated 3 and 5 days after harvest on a scale of 0 to 4 where 0=no infection, 1=1-25%, 2=26-50%, 3=51-75%, and 4=76-100% of fruit with botrytis.  Yield data were also collected from the plots throughout the production season using grower's harvesting schedule.  Mite counts were also taken periodically.

Data were analyzed using analysis of variance and significant means were separated using Tukey's HSD means separation test.

Treating the transplants with different treatment materials and planting in respective beds

Newly transplanted experimental plots.

Chris Martinez (center, front row) and rest of the field crew at Manzanita Berry Farms

Results:

Canopy size: Significant differences (P = 0.002) among treatments were seen only on the first observation date on 26 January, 2015 where TerraClean-treated plants were smaller than some of the treatments.  There were no significant differences (P > 0.05) in treatments on the following observations in February and March, however TerraClean-treated plants recovered and plants were larger in some of the treatments.

Size of the plant canopy on three observation dates.

Plant health: Treatments did not have a significant (P > 0.05) impact on plant health.  Health ratings varied from 4.2 for TerraClean to 4.6 for untreated, BotaniGard, Actinovate, and O-Mega treatments in January.  In February, TerraGrow-treated plants had 4.5 rating and BotaniGard and O-Mega treatments had 4.8.  March ratings varied between 4.8 and 4.9 in all the treatments.  As there were no soilborne diseases during the study period, the impact of the treatments could not be determined, which was the main objective of the study.

 Plant health ratings on three observation dates.

Powdery mildew: Disease severity did not differ among treatments (P > 0.05) on 16 April and 16 June, but significant (P = 0.008) differences were observed on 26 June where BotaniGard-treated plants had the lowest.  When data were compared for the three observation dates, severity rating varied from 1.8 for BotaniGard to 2.24 for TerraClean.

Powdery mildew severity on individual observation dates (top) and combined for three observations (bottom)

Botrytis fruit rot: There were no significant (P > 0.05) differences among treatments on any of the four observation dates or when data were combined for all observations.  In general, fruit rot was less severe 3 days after harvest than 5 days after during the first three observation dates.  When data were combined for the observation dates, HealthySoil treatment had a rating of 1 followed by Met52, NoFly, Actinovate, and TerraClean+TerraGrow with a 1.3 rating for 3 days after harvest.

Severity of botrytis fruit rot 3 and 5 days after harvest on individual observation dates (above) and when data were combined (below).

Spider mites: Mite populations were very low in all the plots during observation period and data were not included.

Fruit yield: While the seasonal yield of total, marketable, or unmarketable berries was not significantly (P > 0.05) different for any of the treatments marketable yields had a wider range than unmarketable yields among treatments.  The lowest marketable fruit yield was seen in TerraClean (35.6 kg or 79.4 lb) and HealthySoil (35.8 kg or 79.8 lb) while the highest yield was seen in Actinovate (40.1 kg or 89.4 lb) followed by untreated control (39.4 kg or 87.9 lb), O-Mega (39.3 kg or 87.6 lb), Met52 (39.2 kg or 87.4 lb), and NoFly (38.7 kg or 86.3 lb) treatments.

Seasonal yields of total, marketable, and unmarketable strawberries per plot. 

This is the first field study evaluating the impact of three popular entomopathogenic fungi along with multiple beneficial microbes on strawberry plant growth, foliar and fruit diseases, and yield.  While differences among treatments were not pronounced, it appeared that some had a positive impact on some of the parameters measured.  It is interesting to note that yields were higher (although not statistically significant) than the grower standard, HealthySoil.  Compared to the grower standard, marketable yield was higher in many other treatments.  Since an untreated situation is not common in a commercial field, using beneficial microbes can be useful.  Although previous field studies evaluated the impact of with the entomopathogenic fungus B. bassiana in strawberries (Dara, 2013; Dara, 2016), a positive impact on plant growth or yield by I. fumosorosea and M. brunneum in commercial strawberries has never been reported earlier. 

Additional studies with different application rates would be useful to understand how beneficial microbes could be exploited more.

Acknowledgments: Thanks to Dave Peck, Manzanita Berry Farms for the collaboration and industry partners for the financial support.  Thanks to Chris Martinez and rest of the field crew at Manzanita Berry Farms and Fritz Light and Tamas Zold for the technical assistance.

http://ucanr.edu/articlefeedback 

References

Amerian, M.R., and W.S. Stewart. 2001. Effect of two species of arbuscular mycorrhizal fungi on growth, assimilation and leaf water relations in maize (Zea mays). Aspects of Appl. Biol. 63: 1-6.

Behie, S.W., and M.J. Bidochka. 2014. Nutrient transfer in plant-fungal symbioses. Trends in Plant Sci. 19: 734-740.

Bolandnazar, S., N. Aliasgarzad, M.R. Neishabury, and N. Chaparzadeh. 2007. Mycorrhizal colonization improves onion (Allium cepa L.) yield and water use efficiency under water deficit condition. Sci. Horticulturae 114: 11-15.

Dara, S. K.  2013.  Entomopathogenic fungus Beauveria bassiana promotes strawberry plant growth and health.  UCANR eJournal Strawberries and Vegetables, 30 September, 2013. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11624)

Dara, S. K. 2016. First field study evaluating the impact of the entomopathogenic fungus Beauveria bassiana on strawberry plant growth and yield.  UCANR eJournal Strawberrries and Vegetables, 7 November, 2016. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22546)

Dara, S. K., S.S.R. Dara, and S. S. Dara.  2016.  First report of entomopathogenic fungi, Beauveria bassiana, Isaria fumosorosea, and Metarhizium brunneum promoting the growth and health of cabbage plants growing under water stress.  UCANR eJournal Strawberries and Vegetables, 16 September, 2016.(http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22131)

Nedorost, L., J. Vojtiskova, and R. Pokluda. 2014. Influence of watering regime and mycorrhizal inoculation on growth and nutrient uptake of pepper (Capsicum annuum L.). VII International symposium on irrigation of horticultural crops, Braun P., M. Stoll, and J. Zinkernagel (eds). Acta Horticulturae 1038:559-564.

Wu, Q.S., and Y. Zou. 2009. Mycorrhizal influence on nutrient uptake of citrus exposed to drought stress. Philippine Agri. Scientist 92: 33-38.