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.
- 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.
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 (above) 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.
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.
- 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>
Twospotted spider mite (TSSM) is a global pest infesting a wide variety of crops. TSSM adapts to new hosts very quickly compared to other arthropods and this ability is attributed to the groups or families of genes that detoxify poisonous plant compounds (Grbić et al., 2011). In just nine generations, TSSM was adapted to a resistant cucumber variety (Gould 1978) and this adaptation allowed them to use potato and tobacco as hosts (Gould, 1979) and imparted cross resistance to three organophosphate pesticides (Gould et al., 1982).
Genetic makeup of TSSM also helps to develop resistance to miticides and it has the highest incidence of resistance to pesticides among arthropods (Van Leeuwen et al., 2010; Grbić et al., 2011). Head and Savinelli (2008) reported that TSSM tops the list of arthropods with pesticide resistance by having resistance to 79 active ingredients in 325 cases based on the arthropod resistance database from Michigan State University by Whalon et al. (2006). However, in the current database, the number of resistance cases for TSSM went up to 498 (Table 1).
Multiple factors that contribute to the success of TSSM, rapid development of pesticide resistance, and the ability to feed on a large number of plant species include the following:
i) Short life cycle and high fecundity that lead to multiple generations in a short time.
ii) Haplo-diploid sex determination system, where males develop from unfertilized eggs and females from fertilized eggs. As a results unfavorable recessive alleles will be removed from mite populations.
iii) Spinning of a strong, but very thin webbing that provide protection against natural enemies
iv) Multiple families of detoxification genes that allow digestion, detoxification, and transportation of toxic metabolites.
v) Lateral transfer of genes from bacteria, fungi, and other organisms through lateral gene transfer which facilitated digestion and detoxification of xenobiotics.
vi) Large number (39) of multidrug resistance proteins compared to a smaller number (9-14) in vertebrates or invertebrates.
Since TSSM is a global pest on multiple hosts, the chances of exposure to pesticides is high, which creates a high selection pressure for resistance. Repeated use of effective pesticides renders them ineffective due to resistance development. Gould et al. (1991) reported slower adaptation of TSSM when a lower level of host plant resistance was combined with natural enemies rather than high host plant resistance alone. Monitoring resistance and adopting integrated pest management (IPM) practices is critical in managing TSSM.
General recommendations for managing TSSM:
- Regularly monitor several parts of the field for mite infestations and make appropriate treatment decision depending on the level and distribution of mite populations and environmental conditions.
- Consider an IPM approach by using biological control options (release of predatory mites), modifying cultural practices (avoiding water stress and excessive nitrogen fertilization), and applying botanical (rosemary oil or other similar products), microbial (BotaniGard, Pfr-97, Met 52, Grandevo, and Venerate), or chemical (Table 2) pesticides.
- Provide refuges that support susceptible mite populations to delay resistance development.
- When applying chemicalmiticides rotate those among different mode of action (MoA) groups. Use softer chemicals when predatory mites are used.
Periodically monitor miticide efficacy and signs of resistance development. If resistance is suspected, conduct a simple bioassay to confirm before field application of the miticide. Collect several leaves samples from different parts of the field with TSSM suspected to have resistance to a particular miticide. Prepare a small quantity of the spray liquid in a container following field application rates. Dip the leaves in the spray liquid and keep them in a covered container (not airtight) in a cool, dry place. Check 48 hours after the exposure to determine the efficacy of or resistance to the miticide based on TSSM mortality.
Bioassay to determine miticide resistance in twospotted spider mites.
Additional information on TSSM and its management in strawberries can be found at:
- Managing spider mites in California strawberries (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13943)
- Efficacy of botanical, chemical, and microbial pesticides on twospotted spider mites and their impact on predatory mites (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18553)
- Predatory mites for managing spider mites on strawberries (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14065)
- Response of predatory mites to chemical, botanical, and microbial miticides in strawberries (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14428)
- Spider mite damage causes unique foliar discoloration in Benicia variety (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11600)
- Multiple handouts on spider mites in strawberries (http://ucanr.edu/meetinghandouts)
- UC IPM Pest Management Guidelines for spider mites in strawberry (http://ipm.ucanr.edu/PMG/r734400111.html)
Gould, F. 1978. Predicting the future rresistance of crop varieties to pest populations: a case study of mites and cucumbers. Environ. Entomol. 7: 622-626.
Gould, F. 1979. Rapid host range evolution in a population of the phytophagous mite Tetranychus urticae Koch. Evolution 33: 791-802.
Gould, F. Carroll, C. R., and Futuyma, D. J. 1982. Cross-resistance to pesticides and plant defenses: a study of the two-spotted spider mite. Entomol. Exp. Appl. 31:175-180.
Grbić, M., Van Leeuwen, T., Clark, R.M., Rombauts, S., Rouzé, P., Grbić, V., Osborne, E.J., Dermauw, W., Ngoc, P.C.T., Ortego, F. and Hernández-Crespo, P. 2011. The genome of Tetranychus urticae reveals herbivorous pest adaptations. Nature, 479: 487-492. DOI: 10.1038/nature10640
Head, G. and C. Savinelli. 2008. Adapting insect resistance management programs to local needs. In: Onstad, D. W. (Ed.) Insect Resistance Management: Biology, Economics, and Prediction, Academic Press, United Kingdom, pp. 89-106.
Van Leeuwen, T., Vontas, J., Tsagkarakou, A., Dermauw, W. and Tirry, L. 2010. Acaricide resistance mechanisms in the two-spotted spider mite Tetranychus urticae and other important Acari: a review. Insect Biochem. Mol. Biol. 40: 563–572.
Whalon, M. E., Mota-Sanchez, D., Hollingworth, R. M., and Duynslager, L. 2006. Michigan State University Arthropod Resistance Database. http://www.pesticideresistance.org/search.php
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)
Acknowledgment: 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>/h4>/h4>