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.
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.
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.
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.
- Author: Surendra K. Dara
- Author: Suchitra S. Dara
- Author: Sumanth S. R. Dara
- Author: Tim Anderson, Dow
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.
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).
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.
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.
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.
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.
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).
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.
Askary H., Y. Carrière, R. R. Bélanger, and J. Brodeur. 1998. Pathogenicity of the fungus Verticillium lecanii to aphids and powdery mildew. Biocon. Sci. Tech. 8: 23-32.
Bark, Y. G., D. G. Lee, S. C. Kang, and Y. H. Kim. 1996. Antibiotic properties of an entomopathogenic fungus, Beauveria bassiana on Fusarium oxysporum and Botrytis cinerea. Korean J. Plant Pathol. 12: 245-250.
Bennett, R. S., D. W. Spurgeon, W. R. DeTar, J. S. Gerik, R. B. Hutmacher, and B. D. Hanson. 2011. Efficacy of four soil treatments against Fusarium oxysporum f. sp. vacinfectum race 4 on cotton. Plant Dis. 95: 967-976.
Dara, S. K. 2013. Entomopathogenic fungus, Beauveria bassiana promotes strawberry plant growth and health. UCCE eJournal Strawberries and Vegetables, 30 September, 2013. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11624)
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. UCCE eJournal Strawberries and Vegetables, 19 September, 2016.
Goettel, M. S., M. Koike, J. J. Ki, D. Aiuchi, R. Shinya, and J. Brodeur. 2008. Potential of Lecanicillium spp. for management of insects, nematodes and plant diseases. J. Invertebr. Pathol. 98: 256-261.
Ownley, B. H., M. R. Griffin, W. E. Klingeman, K. D. Gwinn, J. K. Moulton, and R. M. Pereira. 2008. Beuveria bassiana: endophytic colonization and plant disease control. J. Invertebr. Pathol. 98: 267-270.
Sasan, R. K. and M. J. Bidochka. 2012. The insect-pathogenic fungus Metarhizium robertsii (Clavicipitaceae) is also an endophyte that stimulates plant root development. Amer. J. Bot. 99:101-107.
Sasan, R. K. and M. J. Bidochka. 2013. Antagonism of the endophytic insect pathogenic fungus Metarhizium robertsii against the bean plant pathogen Fusarium solani f. sp. phaseoli. Can. J. Plant Pathol. 35: 288-293./span>
- Author: Surendra K. Dara
- Author: Sumanth S. R. Dara
- Author: Suchitra S. Dara
Entomopathogenic fungi such as Beauveria bassiana (commercial formulations, BotaniGard and Mycotrol), Isaria fumosorosea (NoFly and Pfr-97), and Metarhizium brunneum (Met52) are primarily used for controlling arthropod pests. Research in the recent years evaluated their endophytic (colonizing plant tissues) and mycorrhiza-like (associated with roots) relationship with plants and potential benefits in improving plant growth and health. Studies conducted in California showed that B. bassiana endophytically colonized strawberry plants and persisted for up to 9 weeks in various plant tissues (Dara and Dara, 2015a); promoted strawberry plant growth (Dara, 2013); and negatively impacted green peach aphids through endophytic action (Dara, 2016). Soil application of M. brunneum appeared to have a positive impact on strawberry plants in withstanding twospotted spider mite infestations (Dara and Dara, 2015b). Similarly, M. anisopliae reduced the salt stress in soybean (Khan et al., 2012) and M. robertsii enhanced root growth and nutrient absorption in switch grass and haricot beans (Behie et al., 2012; Sasan and Bidochka, 2012). In another study, nitrogen obtained from an insect host through infection (entomopathogenic relationship) was transferred by B. bassiana and Metarrhizum spp. to a plant through an endophytic or mycorrhiza-like relationship.
Several beneficial microbe-based products are commercially available to promote plant growth under normal or stressful conditions and to boost plant defenses against pests and diseases. However, several mycorrhizae do not form a symbiotic relationship with several cruciferous hosts and mycorrhizae-based products are typically not used in cole crops. If entomopathogenic fungi, which have a great promise for pest management in IPM programs, could also promote plant growth and health through an endophytic or mycorrhiza-like relationship, they will maximize their potential for multipurpose use in crop protection and production and potentially reduce the cost of applying multiple products for multiple purposes.
A study was conducted in 2014 to evaluate the impact of B. bassiana, I. fumosorosea, and M. brunneum on potted cabbage plants growing in artificial light with reduced water.
About 3-week old cabbage (var. Supreme Vantage) transplants (obtained from Plantel Nurseries, Santa Maria, CA) were planted in Miracle-Gro® Moisture Control Potting Mix (NPKFe 0.21-0.07-0.14-0.10) in 650 ml containers. Treatments included BotaniGard ES (1 ml), Met 52 EC (1 ml), NoFly WP (2.5 mg), SumaGrow (2.3 ml), CropSignal (1 ml), Mykos Liquid (0.03 ml), and H2H (10 ml) in 100 ml of water which were added to each container in respective treatments. Miracle-Gro alone was used as the control. Each treatment had 10 plants which were grown under artificial lighting (75 W plant light in each corner). To each container, 50 ml of water was added again on 42, 50, 64, and 81 days after planting. Temperatures during the study were 56o (minimum), 71o (average), and 88o F (maximum).
Data were collected as follows:
- Plant health rating was recorded at 40 and 70 days after planting on a scale of 0 to 5 where 0=dead, 1=weak, 2=moderate-low, 3=moderate-high, 4=good, and 5=very good.
- Plant survival was recorded at 40, 70, and 90 days after planting.
- Shoot and root length were recorded at 90 days after planting by unearthing each plant from the containers.
- Shoot-to-root ratio was calculated.
- Plants from each treatment were placed in paper bags and dried in an oven at 98oF for 8 days. Dry weight (biomass) of the plants was measured before sending them to an analytical lab for nutrient analysis.
Data were subjected to analysis of variance and significant means were separated using Least Significant Difference test. Since some treatments had fewer plants by the end of the study, biomass measurement and nutrient analysis were done together for all the remaining plants and those two parameters were not subjected to statistical analysis.
Plant survival: Beauveria bassiana was the only treatment where all the plants survived for 90 days of the observation period. There was a 10 to 80% mortality in other treatments during the observation period. Highest plant mortality was seen in SumaGrow and H2H treatments (P = 0.001 at 40 days after planting and
Plant health: Plants treated with B. bassiana were significantly and uniformly healthier (P < 0.00001) than the rest of the treatments on both observation dates with a ‘very good' rating. Health of the plants growing in Miracle-Gro with no supplements also had a ‘good' rating and was better than the health of plants in most of the remaining treatments. Plants treated with SumaGrow and H2H had poor health with a ‘weak' rating.
Shoot and root length: Plants treated with B. bassiana and M. brunneum had significantly (P < 0.00001) longer shoots than other treatments. Miracle-Gro-treated plants were shorter than those treated with these two entomopathogenic fungi, but longer than those in the remaining treatments. When root growth was compared, plants growing in Miracle-Gro alone and along with Crop Signal had significantly (P < 0.00001) longer roots than the rest.
Shoot-to-root ratio: Beauveria bassiana and M. brunneum treatments contributed to a significantly (P < 0.00001) higher ratio than the rest of the treatments.
Biomass and nutrient absorption: Plants treated with B. bassiana had relatively higher biomass. When the plant weight as a result of accumulated nutrients was calculated by dividing the weight with respective nutrient content, B. bassiana appeared to have relatively higher output for nitrogen, phosphorus, and potassium based on numerical values. Such an effect for iron was seen in all, except H2H, treatments compared to Miracle-Gro alone. However, these values are only indicative as they were not subjected to statistical analysis.
This is the first report of the direct impact of entomopathogenic fungi on cabbage plant growth. Beauveria bassiana and to some extent M. brunneum had a positive impact on plant growth and health even under reduced water conditions. If they could be used to promote plant growth, improve water and nutrient absorption, withstand saline or drought conditions, increase yields in addition to their typical use as biopesticides, then they can play a critical role as holistic tools in sustainable agriculture.
Acknowledgements: Thanks to Plantel Nurseries Inc. for donating cabbage transplants, and Advanced Soil Technologies, Bioworks Inc, California Safe Soil, Novozymes Biologicals, Reforestation Technologies International, and SumaGrow USA for various treatment materials used in this study.
Behie, S.W., P.M. Zelisko, and M.J. Bidochka. 2012. Endophytic insect-parasitic fungi translocate nitrogen directly from insects to plants. Science 336: 1576-1577.
Dara, S. K. 2013. Entomopathogenic fungus, Beauveria bassiana promotes strawberry plant growth and health. UCCE eNewsletter Strawberries and Vegetables, 30 September, 2013. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11624)
Dara, S. K. and S. R. Dara. 2015a. Entomopathogenic fungus, Beauveria bassiana endophytically colonizes strawberry plants. UCCE eNewsletter Strawberries and Vegetables, 17 February, 2015. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16811)
Dara, S. K. and S. R. Dara. 2015b. Soil application of the entomopathogenic fungus, Metarhizium brunneum protects strawberry plants from spider mite damage. UCCE eNewsletter Strawberries and Vegetables, 18 February, 2015. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16821)
Dara, S. K. 2016. Endophytic Beauveria bassiana negatively impacts green peach aphids on strawberries. UCCE eNewsletter Strawberries and Vegetables, 2 August, 2016. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21711)
Sasan, R.K. and M.J. Bidochka. 2012. The insect-pathogenic fungus Metarhizium robertsii (Clavicipitaceae) is also an endophyte that stimulates plant root development. Amer. J. Bot. 99:101-107./h4>
Beauveria bassiana is a naturally occurring fungus that is pathogenic to several groups of arthropods. It is available in different commercial formulations for pest management in agriculture, nurseries, landscape, greenhouse, turf, and home gardens. BotaniGard ES and 22WP are the conventional formulations and Mycotrol-O was the organic-approved formulation, all distributed by BioWorks, Inc. After the OMRI organic certification for Mycotrol-O expired in August, 2015, the Butte, MT based manufacturer, LAM International, changed the formulation with an approved inert ingredient. Mycotrol ESO and Mycotrol WPO are the two new organic-approved formulations of B. bassiana registered for various pests for different situations. Both formulations have WSDA organic certifications. Unlike Mycotrol-O, ESO and WPO formulations have specific crop uses and it is important to verify labels for appropriate use.
It is similar to BotaniGard ES except for an organic-approved mineral oil carrier. Mycotrol ESO has a shelf life of 18 months and does not require refrigeration. However, as the product contains a live fungus, it is important to avoid exposure to high temperatures. Mycotrol ESO is registered for several agricultural crops and multiple pests except for cranberry girdler.
It is a formulation similar to BotaniGard 22WP except for the inert ingredients. It has a shelf life of 12 months, which is shorter than the ESO formulation, but does not require refrigeration. Avoiding storage in warmer conditions is important due to the live fungus in the formulation. Mycotrol WPO is primarily used for greenhouse, nursery, landscape, interior scape, turf, and container soil applications. Although it is registered for many agricultural crops, due to the lack of application instructions, it cannot be used on them. Unlike Mycotrol-O and ESO, WPO formulation has fewer insects on the label and is not registered for certain species of plant bugs, weevils, all stem-boring Lepidoptera, foliage-feeding Lepidoptera, and leaf-feeding beetles.
Both ESO and WPO formulations have zero preharvest interval and 4 hours of restricted entry interval. They can be tank-mixed with several other insecticides, miticides, fertilizers, and multiple fungicides. An earlier study with BotaniGard ES showed its compatibility with fungicides Merivon, Microthiol Disperss, Rally, Rovral, and Switch (Dara et al., 2014). However, Captan and Thiram were not compatible with B. bassiana.
Beauveria bassiana and other entomopathogenic fungi play an important role in IPM. Several studies showed their potential in managing strawberry and vegetable pests (Dara, 2013; 2015a, b, c, d & e). While entomopathogenic fungi can be used as standalone treatment options in several circumstances, by combining and/or rotating with chemical or botanical pesticides, they serve as an important part of the IPM tool kit for multiple crops against multiple pests.
Bagrada bugs (above) and the glassy-winged sharpshooter (below) killed by Beauveria bassiana. Fungus emerges from the insect cadaver and produces spores which can continue the infection process. (Photos by Surendra Dara)
Western tarnished plant bug (lygus bug) killed by Beauveria bassiana. (Photo by Surendra Dara)
Acknowledgement: Thanks to Daniel Peck, Bioworks, Inc. for the information on new Mycotrol formulations.
Dara, S. K. 2013. Managing aphids on broccoli and thrips on lettuce with chemical and microbial control options. March 27, 2013, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9629
Dara, S. K. 2015a. Efficacy of botanical, chemical, and microbial pesticides on twospotted spider mites and their impact on predatory mites. August 4, 2015, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18553
Dara, S. K. 2015b. Strawberry IPM 2013: managing insect pests with chemical, botanical, and microbial pesticides. October 21, 2015, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19290
Dara, S. K. 2015c. Strawberry IPM 2015: managing insect pests with chemical, botanical, microbial, and other pesticides. October 21, 2015, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19294
Dara, S. K. 2015d. Reporting the occurrence of rice root aphid and honeysuckle aphid and their management in organic celery. August 21, 2015, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18740
Dara, S. K. 2015e. Strawberry IPM 2015: managing insect pests with chemical, botanical, microbial, and mechanical control options. November 30, 2015, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19641
Dara, S.S.R., S. S. Dara, A. Sahoo, H. Bellam, and S. K. Dara. 2014. Can entomopathogenic fungus, Beauveria bassiana can be used ffor pest managmentt when fungicides are used ffor disease management? 23 October, 2014, UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=15671/h4>/span>
A variety of arthropod pests attack strawberries in California and farmers primarily use chemical pesticides for pest management (CDPR, 2014 and Zalom et al. 2014). Recent field studies demonstrated the potential of entomopathogenic fungi, Beauveria bassiana and Metarhizium brunneum in managing important pests such as western tarnished bug, Lygus hesperus in strawberries (Dara 2013a;2014;2015). Entomopathogenic fungi are commonly used as biopesticides where fungal spores cause infections when they come in contact with the target pests. However, these fungi are also reported to endophytically colonize plants (Dara et al., 2013; Behie et al., 2015). Endophytic colonization of B. bassiana in various host plants and the impact on herbivore populations was previously described in some studies (Akello, 2008, Bing and Lewis, 1991, Posada et al., 2007, Tefera and Vidal, 2009, Wagner and Lewis, 2000). An earlier study showed that B. bassiana endophytically colonized strawberry roots, petioles, leaf lamina, pedicels, sepals, and calyxes and persisted up to 9 weeks through soil inoculation (Dara et al., 2013), but its impact on herbivore infestations, especially those with piercing and sucking mouthparts is unknown. A greenhouse study was conducted using green peach aphid, Myzus persicae Sulzer, a minor pest of strawberries, as a model insect to evaluate the impact of endophytic B. bassiana.
Materials and Methods
The study was conducted in a greenhouse using the following treatments: i) untreated control, ii) six weekly soil applications of B. bassiana starting from one week after planting, iii) four weekly foliar applications of B. bassiana starting two weeks after planting, and iv) both soil and foliar applications at respective intervals used with individual applications. Each treatment had four strawberry transplants, obtained from a commercial source and planted in 1 gallon pots (18 cm diameter and 18 cm height) with potting medium composed of a mixture of steam sterilized field soil and perlite. Five grams of Osmocote(R) Slow Release Fertilizer 14-14-14 (Carolina Biological Supply Company, Burlington, NC) was added to each pot followed by watering to the point of saturation. One week after planting, each strawberry plant was infested with 10 pre-adult M. persicae obtained from a greenhouse colony.
For soil treatment of B. bassiana, 1 ml of Mycotrol-O in 100 ml of water was placed around the base of the plant a week after planting and one week prior to aphid infestation. For foliar treatment, 0.25 ml of Mycotrol-O in 100 ml water was sprayed, starting one week after aphid infestation, using a plastic spray bottle until the foliage was thoroughly covered. A polystyrene plate with a hole in the center and a slit across the radius was placed around the base of each plant before administering treatments to avoid cross contamination of soil and foliar treatments. The hole around the plant base was plugged with a ball of cotton.
The number of live and dead aphids, fully expanded leaves, and flower shoots were monitored weekly for a total of seven weeks after artificial infestation and the means for the observation period were calculated. Data were analyzed using ANOVA and significant means were separated using Fisher's Least Significant Difference test. Proportion of live and dead aphids was analyzed after arcsine transformation. Since endophytic colonization of strawberry by B. bassiana was previously reported (Dara et al, 2014), plant tissue was not tested again for the presence of fungus. During the experimental period, average minimum and maximum temperatures were 15.6 and 26.7oC and relative humidity values were 51 and 93%, respectively.
Results indicated that B. bassiana contributed to the mortality of M. persicae through both endophytic and pathogenic modes of action. A significantly higher number of dead aphids was seen on treated plants compared to untreated plants (P = 0.0002). The combination of soil and foliar applications had an additive effect with significantly higher number of dead aphids than soil or foliar applications alone. There was no significant difference in the number (P = 0.0078) or proportion (P = 0.0001) of live aphids or the number of adult aphids (P = 0.0089) between untreated plants and those treated with soil application of B. bassiana. However, there were significantly fewer live aphids where B. bassiana was applied as a foliar spray and a combination of soil application and foliar spray. The impact of treatments on live nymphs was more pronounced with a wider range of significant differences than on live adults. The number of fully expanded leaves and flowering shoots was similar among the treatments (P > 0.05) during the observation period.
* Means followed by the same or no letter within each column are not significantly different at the respective P value in the bottom
Impact of soil and foliar applications of B. bassiana on green peach aphid numbers and strawberry plant
Although entomopathogenic fungi are known to have endophytic interactions with various plant species, how this interaction influences herbivore populations is not fully understood. Several studies shed some light on this new area of research, but they primarily include insects with chewing mouthparts such as the banana weevil, Cosmopolites sorditus on banana (Akello et al., 2008), the corn ear worm, Helicoverpa zea on tomato (Powell et al., 2009), and the European corn borer, Ostrinia nubilalis on corn (Bing and Lewis, 1991, Lewis et al., 1996) except for a recent report of endophytic B. bassiana and Purpureocilium licacinum impacting the survival and reproduction of cotton aphid, Aphis gossypii Glover on cotton (Castillo Lopez et al., 2014). Antibiosis is thought to be one of the mechanisms for the endophytic entomopathogens to affect herbivores (Castillo Lopez et al., 204, Vega et al., 2008).
The current study clearly indicated that B. bassiana affected the mortality of M. persicae as an endophyte and an entomopathogen. Having an additive effect through endophytic interaction as well as infection is useful for increasing pest control efficacy in practical agriculture. Entomopathogenic fungi and other microbial control agents are generally perceived to be less effective than chemical pesticides and improved efficacy through multiple modes of action adds value to microbial control. In an earlier study, greenhouse strawberry plants that received soil application of M. brunneum withstood infestations of twospotted spider mite, Tetranychus urticae Koch, better than untreated plants (Dara and Dara 2015). Endophytic colonization of the fungus could not be determined by surface sterilizing and plating the plant tissue on selective medium, but treated plants performed better than control plants under mite pressure indicating a positive impact of M. brunneum on strawberry plants.
In the current study, while the mortality of aphids was higher with the combined treatment of soil and foliar applications, surviving aphids did not follow the same trend showing slightly higher numbers wherever soil applications were made. In general, plants that received soil application of B. bassiana appeared to be healthier than untreated or foliar treatment alone and although not significantly different, plants that received the soil treatment had a slightly higher number of leaves during the observation period possibly contributing to higher surviving aphids. Other studies conducted in California also support this idea that entomopathogenic fungi, including B. bassiana, promote plant growth (Dara, 2013b, Dara et al. 2014).
This is the first report of the impact of endophytic B. bassiana on the mortality of M. persicae on strawberry laying foundation for additional studies with major pests such as L. hesperus. Entomopathogenic fungi can play a significant role in integrated pest management and studies that elucidate their interaction with plants and pests will help promote their use in sustainable agriculture.
Thanks to Jaclyn Wiley and Melody Carter for their technical assistance and David Headrick, Cal Poly for providing aphids and the greenhouse space for the study.
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