Grower Notes and Pest News
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.
List of treatments, their application rates and frequencies:
- Untreated control: Received no supplemental treatments other than standard grower practices.
- HealthySoil: NPK (0.1-0.1-0.1).
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
Newsly transplanted experimental plots.
Chris Martinez (center, front row) and rest of the field crew at Manzanita Berry Farms
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.
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.
First field study evaluating the impact of the entomopathogenic fungus Beauveria bassiana on strawberry plant growth and yield
Beauveria bassiana is a soilborne entomopathogenic fungus which offers plant protection as a pathogen of arthropod pests (Feng et al., 1994; Dara, 2015). It also appears to have a direct association with plants as an endophyte, colonizing various plant tissues, or through a mycorrizha-like relationship promoting plant health and growth (Bing and Lewis, 1991; Posada and Vega, 2005; Dara, 2013; Dara and Dara, 2015; Lopez and Sword, 2015; Dara et al., 2016;). In a raised bed study conducted in 2013, treating strawberry transplants with B. bassiana resulted in a significant improvement in the plant growth compared to untreated control or treatment with a beneficial microbe-based product (Dara, 2013). To evaluate such an impact in a commercial strawberry field, a study was conducted at Manzanita Berry Farms in Santa Maria in conventional fall-planted strawberries.
Chris Martinez, Manzanita Berry Farms applying B. bassiana to newly planted strawberry crop.
Experimental design included five plots each of the grower standard and periodical soil application of B. bassiana (BotaniGard ES) alternated on consecutive beds. Each plot had 50 strawberry plants. Strawberry variety PS3108 was planted on 27 November, 2013 and B. bassiana treatment was initiated on 2 December, 2013. To prepare the treatment liquid, 0.64 fl oz (18.9 ml) of BotaniGard ES was mixed in 1 gal (3.78 L). About 0.4 fl oz (11.8 ml) of the liquid was applied near the base of each plant (5 cm deep and 2.5 cm away from the plant) in B. bassiana treatment using a handpump sprayer. Application was continued every week until 13 January, 2014 (a total of seven times) followed by six biweekly applications until 7 April, 2014.
To determine the impact of B. bassiana on plant growth, size of the strawberry canopy was measured across and along the length of the bed from every third plant (20 total) within each plot on 21 January, 11 February, and 7 March, 2014. Yield data were collected every 2-3 days from 8 March to 30 June, 2014 following the normal harvest schedule. Data were analyzed using analysis of variance and Tukey's HSD test was used to separate significant means.
Chris Martinez taking canopy measurements.
Canopy size was slightly higher for B. bassiana-treated plants on the first two sampling dates and for the grower standard plants on the last observation date although differences were not statistically significant (P > 0.05). Seasonal total for the marketable berries was slightly higher in the grower standard (101.1 lb or 45.9 kg) than in B. bassiana treatment (44.2 lb or 97.4 kg), but the difference was not statistically significant (P > 0.05). The average weight of marketable berries was 28.8 g from the B. bassiana-treated plots and 28.7 g from the grower standard.
Strawberry canopy (above) and seasonal yield (below) data in B. bassiana-treated and grower standard plots.
In the 2013 raised bed study, roots of the misted tip strawberry transplants were treated 48 hours before planting by applying 1 ml of the Mycotrol-O formulation (2.11X1011 conidia) in 1 ml of water per plant. In the current study, transplants could not be treated before planting and the commercial field application rate used (1.25X109 conidia) was much less than the rate used in the raised bed study. Although multiple applications were made for several weeks during the current study, B. bassiana did not have any impact on plant growth or fruit yields. This was the first commercial field study evaluating the impact of B. bassiana on strawberry plant growth and yield. Plant, soil, and microbe interaction is very complex and is influenced by multiple factors. Additional studies are necessary to understand the potential of B. bassiana and other entomopathogenic fungi in plant production in addition to its role in plant protection.
Acknowledgements: Thanks to Dave Peck, Manzanita Berry Farms for collaboration on the study and Chris Martinez for his technical assistance.
Bing, L. A., and L. C. Lewis. 1991. Suppression of Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae) by endophytic Beauveria bassiana (Balsamo) Vuillemin. Environ. Entomol. 20: 1207-1211.
Dara, S. K. 2013. Entomopathogenic fungus Beauveria bassiana promotes strawberry plant growth and health. UCANR eJournal Strawberries and Vegetables, 30 September, 2013.
Dara, S. K. 2016. IPM solutions of insect pests in California strawberries: efficacy of botanical, chemical, mechanical, and microbial options. CAPCA Adviser 19 (2): 40-46.
Dara, S. K. and S. R. Dara. 2015. Entomopathogenic fungus Beauveria bassiana endophytically colonizes strawberry plants. UCANR eJournal Strawberries and Vegetables, 17 February, 2015.
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, 19 September, 2016.
Feng, M. G., T. J. Poprawski, and G. G. Khachatourians. 1994. Production, formulation and application of the entomopathogenic fungus Beauveria bassiana for insect control: current status. Biocon. Sci. Tech. 4: 3-34.
Lopez, D. C. and G. A. Sword, G. A. 2015. The endophytic fungal entomopathogens Beauveria bassiana and Purpureocillium lilacinum enhance the growth of cultivated cotton (Gossypium hirsutum) and negatively affect survival of the cotton bollworm (Helicoverpa zea). Biol. Control 89: 53-60.
Posada, F. and F. E. Vega. 2005. Establishment of the fungal entomopathogen Beauveria bassiana (Ascomycota: Hypocreales) as an endophyte in cocoa seedlings (Theobroma cacao). Mycologia 97: 1195-1200.
After last year's release of the iOS version of the first IPMinfo app, several improvements have been made for the Android version, which was released on 30 September, 2016. One main difference is that the current app is a dynamic one, which requires Internet connection to access the content. This dynamic nature allows real-time updates to the contents of the app that will be reflected immediately.
Here are some key features of the app:
-An option to add content in multiple languages. Currently has strawberry pest information in English and Spanish and disease information in English. User can select the language of their choice and change as needed.
-Information about multiple crops can be accessed. Currently has strawberry and lettuce will be the next crop to be added. User will have the option to select the crop or crops they are interested so that device memory is used only for appropriate choices.
-In addition to pests and diseases, weed and disorder information will also be included.
-Search feature allows selection of a particular topic of interest.
-Access to extension meeting presentations, handouts, YouTube videos, and electronic journals “PestNews” and “Strawberries and Vegetables”.
-An option to provide feedback.
-The notification feature allows sending alerts about updates, new extension articles, meetings, and anything else to the users. Users must turn the notification feature on for this feature to work. These notifications are designed to show up on smart watches as well.
The main goal of IPMinfo is to provide a single point access to pest management information about multiple crops and other extension material so that users do not have to search multiple resources to obtain that information. When details of different crops in multiple languages are added, IPMinfo will serve as powerful resource for pests, diseases, weeds, and disorders and their identification and management.
User can select the crop/crops of their interest. A specific topic can also be searched.
List of diseases, and symptoms and management options for each disease.
Disease symptoms and management options.
List of arthropod pests and their biology (above), damage, and management options (below).
Feedback about the app can be submitted through this feature.
Different information sources can be access from the menu options (above). Articles from eJournals (below).
Adult and nymphs of the green peach aphid, Myzus persicae (Photo by Jack Kelly Clark, UC IPM)
Different species of aphids infest celery and celeriac crops in California. The black bean aphid, Aphis fabae, the foxglove aphid, Aulacorthum solani, the green peach aphid, Myzus persicae, the hawthorn or parsley aphid, Dysaphis apiifolia, and the cotton/melon aphid, Aphis gossypii are among the aphids that could cause damage. Damage includes distorted or stunted plant growth at high numbers, vectoring viral diseases, and contamination of the produce with honeydew secretion and debris.
A study was conducted at Babe Farms, Santa Maria to evaluate the efficacy of various chemical pesticides against aphids. Field was planted in celeriac variety Brilliant on 15 June, 2016. Treatments included i) untreated control, ii) Actara 4 oz/ac, Beleaf 50 SG 2.8 oz/ac, iii) Sequoia 4.5 fl oz/ac, v) Sivanto 200 SL 14 fl oz/ac, and vi) Actara 4 oz + Beleaf 2.8 oz + Radiant SC 8 fl oz/ac as the grower standard. Induce was used as a surfactant at 0.25% vol/vol rate. Treatments were administered on 14 and 25 July and 6 August in 80 gallons/acre of spray volume using a standard spray equipment. Each treatment had eight 38” wide and 100' long beds that were replicated four times and arranged in a randomized complete block design.
Experimental design - six treatments replicated four times
Pre-treatment aphid counts were taken on 13 July and post-treatment counts were taken on 22 and 29 July and 9 August, 2016. On each observation date, 20 random plants from the middle two rows of each plot were gently beaten with the lid of a plastic container and aphids dislodged into the container were recorded.
Data were analyzed using Analysis of Variance model in Statistix software and significant means were separated using Tukey's HSD test.
Only green peach aphids were seen on celeriac during the study. Their numbers were very low and uniform (P = 0.15) before the treatments were initiated (Table 1). After the first spray, there were no aphids in plots treated with Beleaf and it was significantly lower (P =0.0009) than untreated control and Actara treatment. Sequoia was the next best treatment, but it had significantly lower aphids than Actara treatment. Due to a sampling error, data collected after the second spray were excluded from the study. After the third spray, aphid numbers declined only in plots treated with Beleaf and Sequoia and increased at varying degrees in other treatments. Significantly lower (P < 0.00001) number of aphids were present in Beleaf and Sequoia than Actara, Sivanto, and Actara+Beleaf+Radiant treatments. Combination of different chemicals appeared to perform worse than some of the chemicals that were applied independently.
Mean number of aphids per plant (above) or 20 sampled plants (below) before and after pesticide treatments
When percent change in aphid numbers from pre-treatment counts to the counts after the third spray were compared, Beleaf was the only treatment that caused a 33% reduction. Sequoia treatment limited the population build up to a minimum level compared to the rest of the treatments.
Percent change in aphid numbers from pre-treatment counts to post-third spray application
This study demonstrated the efficacy of different chemical pesticides against green peach aphid in celeriac. It was not clear why the combination of some chemicals failed to bring down aphid populations, but results warrant caution while choosing compounds for tank mixes. It is important to avoid repeated use of the best chemical compounds to reduce the risk of resistance development. Select some of the effective chemicals and use them in combination or rotation with botanical and microbial pesticides. Regular monitoring, adopting cultural practices that might reduce pest populations, conservation of biological control agents, and timely application of botanical, microbial, and chemical pesticides, and other appropriate measures are critical components of a sound integrated pest management program.
This study was originally designed for evaluating the efficacy of chemical pesticides against the western tarnished plant bug (lygus bug), Lygus hesperus, which is becoming a problem in vegetable crops such as lettuce, celery, and celeriac. Random sampling in some areas of the field, prior to the initiation of the study, showed a few western tarnished bugs, but due to their negligible numbers thereafter, meaningful results could not be obtained from the study.
Acknowledgements: Thanks to Jason Gamble, Babe Farms, Santa Maria for his collaboration, Bayer CropSciences, Dow AgroSciences, FMC, and Syngenta for the support of the study, and Tamas Zold and Danielle Cadena for the technical assistance.
First report of three entomopathogenic fungi offering protection against the plant pathogen, Fusarium oxysporum f.sp. vasinfectum
Entomopathogenic fungi such as Beauveria bassiana, Isaria fumosorosea, and Metarhizium brunneum play an important role in managing several arthropod pests on multiple crops. Multiple genera of entomopathogenic fungi are available as biopesticides and used in organic and conventional agriculture. Compared to chemical pesticides, entomopathogenic fungi-based pesticides are expensive. While they are excellent tools in integrated pest management (IPM) approaches against several pests, their high cost relative to chemical pesticides can be a hindrance to their widespread use. Exploring their multipurpose use in promoting plant growth and protecting plants from pathogens can increase their acceptance as farmers can get multiple benefits beyond arthropod management when they use entomopathogenic fungi.
Some studies showed the positive impact of entomopathogenic fungi on promoting plant growth and health (Sasan and Bidochka, 2012; Dara, 2013; Dara et al. 2016). Other studies that demonstrated antagonistic effect of entomopathogenic fungi against non-arthropod pests include, B. bassiana against Fusarium oxysporum and Botrytis cinerea (Bark et al., 1996) and Rhizoctonia solani and Pythium myriotylum (Ownley et al. 2008), Lecanicillum lecanii (=Verticillium lecanii)against cucumber powdery mildew, Podosphaera fuliginea (=Sphaerotheca fuliginea) (Askary et al., 1998), Lecanicillium spp. against plant pathogens and parasitic nematodes (Goettel et al., 2008), M. robertsii against Fusarium solani f. sp. phaseoli (Sasan and Bidochka, 2013). These reports show the potential of entomopathogenic fungi in serving multipurpose role in improving plant growth and protecting against multiple groups of pests.
A new greenhouse study was conducted to evaluate the efficacy of B. bassiana (BotaniGard), I. fumosorosea (Pfr-97), and M. brunneum (Met 52) in comparison with other beneficial microbe- (Actinovate and MBI 110) or plant extract-based (Regalia) products in providing protection against a plant pathogen. Cotton was used as the model plant and F. oxysporum f. sp. vasinfectum Race 4 (FOV Race 4) was used as the plant pathogen in this study.
Pima cotton seed of the variety Phy830 (Phytogen) susceptible to FOV Race 4 were planted in potting mix 0.33X103 CFU/g of FOV Race 4 in seedling trays. Healthy potting mix was used as untreated control. Six products, listed below, were applied in three regimens based on foliar application rate (10 ml of the treatment liquid calculated based on 100 gallons of spray volume/ac) or soil application rate (10 ml of the treatment liquid with product calculated based on the surface area of the cell at the soil application rate per acre) to each cell of the tray. Each treatment had 16 cells (or seedlings) and was replicated four times.
- Healthy potting mix (negative control)
- Potting mix with FOV Race 4 (positive control)
- Potting mix with FOV Race 4 + BotaniGard ES (B. bassiana Strain GHA) 2 qrt/ac
- Potting mix with FOV Race 4 + Met 52EC (M. brunneum Strain F52) 2 (foliar rate) and 2.5 (soil rate) qrt/ac
- Potting mix with FOV Race 4 + Pfr-97 20% WDG (I. fumosorosea Apopka Strain 97) 2 lb/ac
- Potting mix with FOV Race 4 + Actinovate AG (Streptomyces lydicus WYEC 108) 54 oz/ac
- Potting mix with FOV Race 4 + Regalia (Extract of Reynoutria sachalinensis) 4 qrt/ac
- Potting mix with FOV Race 4 + MBI 110 (developmental product from Marrone Bio Innovations) 4 qrt/ac
Treatments were applied in the following three regimens. Soil application rate was calculated based on the surface area of each seedling cell (2.25 square inches) compared to one-acre rate and delivered in 10 ml of purified water with 0.01% Dyne-Amic as a surfactant. Foliar rate was calculated based on 100 gallons/ac spray volume and each cell received 10 ml. Untreated control and potting mix with plant pathogen received water with Dyne-Amic.
Regimen A - 10 ml of water or treatment liquid at soil application rate administered right after planting cotton seed.
Regimen B - 10 ml of water or treatment liquid at soil application rate administered right after and 1 and 2 weeks after planting.
Regimen C – 10 ml of water or treatment liquid at foliar application rate administered right after planting.
Seedling trays were arranged on a greenhouse bench and a sprinkler system irrigated trays for 5 min each day at noon. Plant health and growth conditions were monitored 3, 4, and 5 weeks after planting based on the following scale.
0 - Did not germinate or dead or necrosis of cotyledons/leaves and hypocotyl/stem
1.0 - Stem green, but dying leaf/leaves
1.5 - At least one green leaf and cotyledons/other leaves necrotic
2.0 - Green new leaves and yellowing cotyledons/older leaves
2.5 - Green and bigger new leaves with slightly yellowing older leaves
3.0-4.5 - Varying levels of healthy plant
5.0 - Very healthy plant with optimal growth
Data were analyzed using ANOVA model and significant means were separated using the Least Significant Difference (LSD) test.
Treatments were separated by an empty row to prevent cross contamination. Experimental set up at the time of planting (above) and 1 week after planting (below).
Experiment 2 weeks after planting (above).
Symptoms of Fusarium oxysporum f. sp. vasinfectum appear by the third week after planting and advance by the fifth week (below).
Results and discussion
In general, there was a positive impact of treatments on reducing the severity of FOV Race 4 in cotton seedlings, but it varied with time and among treatment regimens. Negative control plants did not show any symptoms of infection – yellowing, necrosis, or wilting - and consistently maintained a high health rating of about 4.8 out of 5.0 (Table 1).
Table 1. Plant health rating 3, 4, and 5 weeks after planting in three treatment regimens.
Regimen A: Treatments were significantly different (P < 0.00001) on all observation dates, but when negative control was disregarded, differences were seen only on the first observation date, which was 3 weeks after planting. Pfr-97, Met 52, and Actinovate resulted in a significant improvement in the plant health compared to the other treatments. On the following observation dates, plant health rating was higher in all treatments compared to the positive control with FOV Race 4, but the differences were not statistically significant.
Refer to Table 1 for statistical significance between treatment means in Regimen A.
Regimen B: In this regimen, where treatments were applied three times at a weekly interval starting from the time of planting, plants treated with Pfr-97, Met 52, and Actinovate a better health rating than the positive control throughout the observation period. MBI 110 was also better than the positive control 3 weeks after planting, but not afterwards. Plant health in Regalia and BotaniGard treatments was better than FOV Race 4 alone, but it was not significantly different.
Refer to Table 1 for statistical significance between treatment means in Regimen B.
Regimen C: This regimen aimed the impact of treating the soil with a higher concentration (based on foliar application rate) of treatments. BotaniGard-treated plants were significantly healthier than MBI 110, Pfr-97, Actinovate, and FOV Race 4 alone on 3 weeks after planting and all the treatments (excluding the positive control) on 4 and 5 weeks after planting.
Refer to Table 1 for statistical significance between treatment means in Regimen C.
Treatments compared among all regimens: When treatments were analyzed by combining all regimens, Met 52, Pfr-97, BotaniGard, and MBI 110 significantly improved plant health over FOV Race 4 alone, 3 weeks after planting (Table 2). However, BotaniGard provided significantly higher protection than all other treatments against FOV Race 4 during the rest of the observation period.
Table 2. Efficacy of treatments 3, 4, and 5 weeks after planting (WAP) when data from different regimens were combined.
Comparing regimens: Data were combined among all treatments and analyzed to compare the efficacy of different regimens. Multiple applications of beneficial microbe or plant extract based pesticides at low concentration or single application of a higher concentration were better than single application of lower concentration especially 4 and 5 weeks after planting (Table 3).
Table 3. Efficacy of different regimens against Fusarium oxysporum f. sp. vasinfectum infection.
Results suggest that non-chemical treatment options used in the study provide some level of protection against the plant pathogen FOV Race 4. It is very important to note that one or more entomopathogenic fungi antagonized FOV Race 4 equal to or better than other products that are based on beneficial microbes or plant extracts known to have fungicidal effect. Bennett et al. (2011) compared endomycorrhizal product AM120 based on Glomus spp. with chemical fumigants (methyl bromide, chloropicrin, 1, 3-dichloroprepene, and metam-sodium) and solarization in multiple field studies. Efficacy of these treatments varied in different experiments and among cotton varieties. While conventional treatments typically provided superior protection against FOV Race 4, mycorrhizae at times was comparable to some of the other treatments in some instances. Even if fumigants are used before planting for a healthy start, periodic soil treatment with beneficial microbes could help maintain plant health for the rest of the crop season.
This is the first study where B. bassiana, I. fumosorosea, and M. brunneum were compared with other non-chemical alternatives against a plant pathogen and demonstrating their potential in offering plant protection. These results shed light in a developing area of science where alternative uses for entomopathogenic fungi are explored. Additional experimentation with different concentrations of the plant pathogen and beneficial microbes would expand our understanding of their interactions.
Acknowledgments: Thanks to BioWorks, Inc., Certis USA, Marrone Bio Innovations, Monsanto BioAg, and Valent BioSciences for providing biopesticide samples used in the study.
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