- Author: Surendra K. Dara
Strawberry is the 6th most important agriculture commodity in California, contributing to 88% of the fresh market and 94% of the processed strawberries produced in the US (USDA-NASS, 2012). According to the Pesticide Action Network database, 9.3 million pounds of pesticides were used in 2009 in California for controlling pests, diseases, and weeds (www.pestinfo.org). Arthropod pests such as lygus bug, thrips, twospotted spider mite, and whitefly are among the important targets that require a significant amount of pesticide applications. Finding effective non-chemical alternatives is essential for ensuring environmental safety and sustainable pest management. Since some of the non-chemical solutions can be less effective or slow in their activity compared to some of the chemical pesticides, a strategy to maximize the potential of all options is essential.
A large scale field study was conducted in Santa Maria in an attempt to incorporate a neem-based botanical insect growth regulator, azadirachtin and an insect-killing fungus, Beauveria bassiana into strawberry IPM. Combining or alternating these materials with chemical pesticides can be a practical and more acceptable solution in providing effective pest management as well as reducing chemical pesticide usage.
Before going into the details of this study, here is a brief introduction to azadirachtin and microbial control.
Azadirachtin
Azadirachtin is a secondary metabolite in neem (Azadirachta indica) seeds produced from the seed cake that remains after extracting neem oil. Azadirachtin is a tetranortriterpenoid which is similar to the molting hormone, ecdysone and its homologs in insects. Azadirachtin blocks these hormones and interferes with the molting. Azadirachtin may also act as feeding deterrent.
Microbial control
Microbial control is a part of pest management that involves using microorganisms that are pathogenic to arthropod pests. These microorganisms include bacteria (e.g. Bacillus thuringiensis and Serratia marcescens), fungi (e.g. B. bassiana, Isaria fumosorosea, and Metarhizium brunneum), viruses (e.g. nucleopolyhedroviruses and granuloviruses), nematodes (e.g. Heterorhabditis bacteriophora and Steinernema carpocapsae) and other such organisms that control pest populations.
Mode of infection
In general, each group of pathogens is specific to or effective against a particular type of pest. Entomopathogenic fungi like B. bassiana are especially ideal for sucking pests such as the lygus bug, a major pest of strawberries. Unlike entomopathogenic bacteria and viruses which need to be ingested by the target pest, fungal pathogens cause infection when they come in contact with their host. Entomopathogenic fungal spores can germinate on various surfaces when there is sufficient moisture. When they come in contact with insect cuticle (skin), they produce an appressorium or a penetration peg and enter the insect body through mechanical pressure and enzymatic degradation of the cuticle. Upon successful entry into the host, fungus multiplies as hyphal bodies, invades the host tissue, and causes mortality. One conidial spore is all it takes to cause infection for most fungi, but arthropods have their own immune system and try to ward off the invaders. In reality, infection is usually caused by multiple spores which increase the chances of invasion. Dead arthropods either stick to the plant surface or fall off the plant and fungus emerges from the cadavers producing more spores for further infection.
Potential of azadirachtin and microbial control in strawberries
Both azadirachtin and B. bassiana are commercially available for both organic and conventional agriculture and are effective against several strawberry pests or similar species (Ludwig and Oetting, 2002, McGuire et al, 2006, Pearsall and Hogue, 2000, Quesada-Moraga et al, 2006, Shi et al, 2008, Von Elling et al, 2002). Additionally, Central Coast weather is ideal with its mild temperatures, foggy conditions, and condensation on plants is favorable for insect pathogenic fungi. Botanical and microbial control options can be an excellent addition to the IPM program especially when controlling lygus bug with chemical insecticides alone has been a major challenge.
Since microbial control agents have a different mode of action than chemical pesticides, they can take longer to cause pest mortality. Fungi like B. bassiana take 2-3 days to infect and kill their hosts and this is comparable to the time that chemical insect growth regulators such as novaluron take to reduce pest populations.
In light of promising results from preliminary studies (Dara, 2011), large scale field studies were conducted on fall planted strawberries in 2012 with a particular emphasis on lygus control.
Field studies with azadirachtin and B. bassiana
A field study was conducted with chemical insecticides (neonicotinoid, pyrethroids, and insect growth regulator), and B. bassiana alone, in combination with azadirachtin and reduced rates of two chemical pesticides. The combination of azadirachtin and B. bassiana targets both nymphal and adult stages. Chemical pesticides at reduced rates help weaken the insects and improve infection by B. bassiana.
This study was conducted on a conventional strawberry field at Manzanita Berry Farms. Cultivar PS-4634 was transplanted in November, 2011. Treatments included, i) untreated control, ii) acetamiprid at 3 oz/ac, iii) novaluron at 12 fl oz/ac + bifenthrin at 16 oz/ac, iv) B. bassiana at 2 lb/ac, v) B. bassiana at 2 lb/ac + azadirachtin at 8 fl oz/ac, vi) B. bassiana at 2 lb/ac + fenpropathrin at 5.3 fl oz/ac (half the label rate), vii) B. bassiana at 2 lb/ac + acetamiprid at 1.5 oz/ac (half the label rate), viii) azadirachtin at 8 fl oz/ac, and ix) azadirachtin at 16 fl oz/ac, all in 50 gallons of spray volume. Each plot was 75' long and 7 beds wide and replicated four times in a randomized block design. Treatments were applied using tractor-mounted spray equipment on July 31, August 8, and August 15. Observations were made 5 or 6 days after each spray application to monitor lygus bug, twospotted spider mite, whitefly, thrips, aphids, and various natural enemy populations using standard sampling protocols. Big-eyed bug, damsel bug, lacewing, lady bug, minute pirate bug, parasitic wasp, and spiders were the natural enemies that were recorded during the observation period.
It should be noted that not all chemical treatments in this study were meant to be effective against all target pests, but pest counts from all treatments are presented for comparison. Although observations were made after each spray application, data are presented as pre- and post-treatment averages to summarize results.
Aphids – There was more than a fivefold increase in untreated control during the treatment period. During this time, acetamiprid caused nearly 78% reduction and the combination of B. bassiana and half the label rate of acetamiprid caused about 44% reduction in aphid numbers. Among the remaining treatments where aphid populations increased, the combination B. bassiana and azadirachtin limited the increase to 19%.
Lygus bugs – Total number of nymphs and adults was similar in untreated control during the experimental period. Acetamiprid caused an overall reduction of 86% in lygus populations from three spray applications. Beauveria bassiana caused 58% reduction in lygus numbers with the first application and only 11% with the second one. It could not limit increasing numbers afterwards. However, the combinations of B. bassiana with azadirachtin and acetamiprid caused nearly 70% reduction in lygus bugs. While the lower rate of azadirachtin was similar to untreated, the higher rate caused a 60% reduction in lygus numbers.
Twospotted spider mites – In general, mite populations were very low during the observation period with some increase after the treatments were initiated. Not having a chemical miticide in the study limits meaningful treatment comparisons. While no treatment caused a reduction in mite populations, the combination of B. bassiana and azadirachtin seemed to limit the increase in egg numbers and the combination of B. bassiana and half the label rate of fenpropathrin limited the increase in mobile stages.
Thrips – There was more than a threefold increase in thrips numbers in untreated control during the observation period. Their numbers also increased in treatments, but it was relatively less in acetamiprid followed by the combinations of B. bassiana with the reduced rate of fenpropathrin and azadirachtin.
Whiteflies – There was a general reduction in whitefly adult numbers during the observation period. Compared to other treatments, acetamiprid alone and along with B. bassiana seemed to cause more reduction although it was not statistically significant.
Natural enemies – All species of natural enemies were combined for the comparison. There was a general decline in their numbers during the observation period. Although not statistically significant, the reduction appeared to be limited in plots treated with B. bassiana and azadirachtin compared to other treatments.
Although statistically significant differences among treatments could not be found with all pests, a large scale field study such as this demonstrates the potential of B. bassiana and azadirachtin in strawberry IPM. These materials help reduce the chemical pesticide use and the risk of pesticide resistance when substituted for one or more chemical treatments. Additionally, B. bassiana can improve the overall pest management when used in combination with chemical pesticides and ease the challenge of controlling lygus bug with chemical pesticides alone.
This study clearly demonstrates the potential of microbial and botanical products in strawberry IPM and warrants additional field studies.
Acknowledgements
Thanks to Dave Peck, Manzanita Berry Farms, for his collaboration and valuable support with this study. I also acknowledge the financial support of BioSafe Systems, Bioworks, Inc., Chemtura, and United Phosphorus which made this research possible.
References
Dara, S. 2011. Exploring the potential of an entomopathogenic fungus for strawberry pest management. CAPCA Advisor, October issue, pp 28-33.
Ludwig, S. W. and R. D. Oetting. 2002. Efficacy of Beauveria bassiana plus insect attractants for enhanced control of Frankliniella occidentalis (Thysanoptera: Thripidae). Fla. Entomol. 85: 270-272.
McGuire, M.R., J. E. Leland, S. K. Dara, Y.-H. Park and M. Ulloa. 2006. Effect of different isolates of Beauveria bassiana on field populations of Lygus hesperus. Biol. Control 38: 390-396.
Pearsall, L. A. and E. J. Hogue. 2000. Use of azadirachtin as a larvicide or feeding deterrent for control of western flower thrips in orchard systems. Phytoparasitica 28: 219-228.
Quesada-Moraga, E., E.A.A. Maranhao, P. Valverde-García, C. Santiago-Álvarez. 2006. Selection of Beauveria bassiana isolates for control of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum on the basis of their virulence, thermal requirements, and toxicogenic activity. Biological Control 36: 274-287.
Shi, W-B., L-L. Zhang, and M-G. Feng. 2008. Field trials of four formulations of Beauveria bassiana and Metarhizium anisopliae for control of cotton spider mites (Acari: Tetranychidae) in the Tarim Basin of China. Biol. Control 45: 48-55.
USDA-NASS. 2012. California agricultural statistics. 2011 crop year.
Von Elling, K., C. Borgeneister, M. Sétamou, and H.-M Pehling. 2002. The effect of NeemAzal-T/S®, a commercial neem product, on different developmental stages of the common greenhouse whitefly Trialeurodes vaporariorum Westwood (Hom., Aleyrodidae). J. Appl. Entomol. 126: 40-45.
- Author: Surendra Dara
Bagrada bug has an interesting scientific name - Bagrada hilaris. This bug is native to Africa and the genus probably represents the ancient Bagradas River in North Africa. Species name ‘hilaris' means cheerful, merry or joyful in Latin. Although such feelings are not associated with this pest considering its damage to cole crops in agricultural fields and home gardens, it probably refers to the pretty color pattern of the insect.
As the spring season approaches, yellow patches of wild mustard brighten the landscapes and blooms of alyssum whiten the gardens. Both are favorite hosts of the invasive Bagrada bug which has moved as far up as Monterey County. Growers and gardeners should be on the lookout for the Bagrada bug which mainly feeds on cole crops and other hosts such as alyssum and wild mustard.
Bagrada bug females deposit barrel-shaped whitish eggs on the foliage and in the soil in clusters. Eggs hatch and nymphs go through five instar stages before becoming adults. Early instar nymphs have black and orange coloration and the late instars and adults have black, orange, and white patterns. Females are larger than males.
Life stages of the Bagrada bug. Barrel shaped eggs, different nymphal instars, and adult. Younger nymphs only have black and orange coloration while the later instars and adults develop white markings as well. (Eggs and the last instar photos by Eric Natwick and the rest by Surendra Dara)
Correct identification is important in handling any pest as the control strategies can vary for different pests. Some sources incorrectly refer Bagrada bug as a synonym of harlequin bug. They look similar, but they belong to two different genera and are of different sizes. The adult harlequin bug [Murgantia histrionica (Hahn)] is probably 6-8 times as big as the Bagrada bug adult.
Compared to the harlequin bug, Bagrada bug is quite small. Adult Bagrada bug on the pronotum of the adult harlequin bug. (Photo by Surendra Dara)
Organic control options: Preliminary data from my multiple laboratory assays indicate that commercial formulations of three entomopathogenic fungi, Beauveria bassiana (strain GHA), Metarhizium anisopliae (strain F52), and Paecilomyces fumosoroseus (strain FE9901) caused good mortality or infection in Bagrada bug adults. Additional assays will be conducted before publishing the data.
Bagrada bug adults infected and killed by commercially available formulations of three insect pathogenic fungi. Fungal spores penetrate the insect, spread through the body, kill the insect, and emerge from the cadaver producing more spores.
Beauveria bassiana emerges from the recently killed Bagrada bugs (above). White hyphal growth can be seen on the thorax, legs, and other body parts. Fungus continues to emerge from the cadavers, grow, and produces spores (below, four days after the above).
- Author: Surendra K. Dara
“Integrated pest management (IPM) is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pesticides are used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism. Pest control materials are selected and applied in a manner that minimizes risks to human health, beneficial and nontarget organisms, and the environment.” UC IPM
IPM is pivotal in providing effective and sustainable management of pests and diseases in various crops. University of California has an extensive IPM program with sound science-based solutions for numerous pests, diseases, and weeds. One of our approaches is to provide guidelines for year-round IPM to help mitigate environmental health issues while providing practical management options.
Year-round IPM program enables the growers to make appropriate decisions before and throughout the growing season to avoid or mitigate pest problems. From choosing the right field or ideal cultivar to timely harvesting of fruit or postharvest field sanitation are important in avoiding several problems. Here is a brief overview of year-round strawberry IPM.
Before planting
Crop rotation: It eliminates the availability of host plants for pests or diseases. Rotating strawberries with nonsusceptible hosts minimizes the risk of diseases such as angular leaf spot, anthracnose, charcoal rot, Fusarium wilt, and Verticillium wilt.
Field selection: A clean, well-drained field free of diseases or away from sources of pest infestations will reduce the risk of some diseases like Fusarium wilt and pests like lygus bug and spider mites. Fields close to second-year strawberries or can have early infestations of certain pests.
Cut-back strawberry field to extend the production season. They harbor pests that can contribute to infestation of the nearby new fields. (Photo by Surendra Dara)
Fumigation or solarization: Several soilborne diseases and weeds can be effectively controlled through fumigation or solarization (where practical). Studies with non-chemical fumigation techniques such as anaerobic soil disinfestation are under way and can provide alternative solutions to chemical fumigants.
Cultivar selection: Choose a cultivar that is resistant to major pests and/or diseases.
Weed management: Several flowering weeds serve as a source of lygus bugs. Managing such weeds in winter reduces the risk of lygus bug.
Plastic mulch: Using a mulch that promotes healthy plant growth helps plants withstand some disease and pest issues.
At planting
Clean and strong transplants: Angular leaf spot, anthracnose, common leaf spot, phytophthora crown rot, powdery mildew, and pallidosis-related decline of strawberry are among the diseases that can be introduced to the production fields through infected transplants. Pests like spider mites and cyclamen mites can also be brought in through transplants. Inadequate or excessive chilling of transplants can result in reduced yields and predispose plants to pest or disease problems. Obtaining transplants from a reputable nursery is always a good investment.
Planting: Adequate spacing and other care while planting are important for optimal plant growth and yield as well as reducing the risk of certain diseases.
After planting
Irrigation: Since strawberries are sensitive to salinity, good water source is important for plant health. Excessive drip or overhead irrigation causes several disease problems such as angular leaf spot, common leaf spot, and red stele. Water stress can weaken plants and worsen the spider mite problem.
Nutrition: Optimal fertilizer supply is important for a healthy crop and good yields. Excessive nitrogen application can worsen some pest problems or diseases like powdery mildew and Verticillium wilt.
Sanitation: Removal of infected or old fruit or plant material is important for minimizing botrytis fruit rot, leather rot, mucor rot, and Rhizopus fruit rot. This practice also important in managing spotted-wing drosophila or other such pests.
Removing dead and dried leaves and leftover berries as a part of good field sanitation rotine. (Photo by Surendra Dara)
Regular monitoring: Regularly monitoring fields for pest, disease or other problems and taking preventive or proactive measures is critical. Proper sampling techniques are important for making treatment decisions.
Pesticides: Timely application of right pesticides is critical in preventing and minimizing the problems. Rotating chemicals with different modes of action increases the control efficacy and reduces the risk of resistance. If insecticide resistance is suspected, test over a small area or on suspected populations before large scale application.
Biological control: Conserve natural enemies by providing alternate hosts as refuges and by using softer chemicals. Good natural enemy populations play a major role in managing pest populations. Predatory mites are effective in controlling spider mites, but choosing the right species at the right time is important.
Releasing the right species of the predatory mite appropriate for the season can play a major role in controlling spider mites. (Photo by Surendra Dara)
Microbial control: In recent field studies, the entomopathogenic fungus, Beauveria bassiana showed a potential for managing aphids, lygus bug, and spider mites.
Botanical pesticides: Recent field trials produced promising results with azadirachtin, a neem-based insect growth regulator in managing some pests including lygus bug.
Other measures and all-time care with good agricultural practices are important for a successful IPM. IPM is an ecosystem-based strategy for a long-term prevention of pests or their damage through a combination of various techniques. Pesticides are used only as necessary with appropriate materials that have minimal risk to humans, non-target organisms, and the environment.
Additional details on various pests, diseases, and weeds, sampling procedures, survey forms, management options, and year-round strawberry IPM program can be found at the following UC resources:http://www.ipm.ucdavis.edu/PMG/C734/m734yi01.html and http://www.ipm.ucdavis.edu/PMG/selectnewpest.strawberry.html.
View new year-round IPM program video & year-round IPM programs to protect cole crops and pistachio from agricultural pests
Got pests and want to use integrated pest management? Use a year-round IPM program. If you're not familiar with what a year-round IPM program is, think of it as a checklist for the agricultural pest management activities you should be doing throughout the season. Take the new video tour “Using Year-Round IPM Programs” to explore the benefits and uses of IPM in field, orchard, and vineyard crops. Managing pests in Cole Crops and Pistachio? View our two newest year-round IPM programs.
Monitoring the most important pests, making management decisions, and planning for the following season are all activities in the year-round IPM programs. Even better are how they connect to the Pest Management Guidelines so you can read about the details…how to monitor, what the treatment thresholds are, or the best pesticide to use.
One of the basic IPM principles is to choose the best pesticide for the situation. The year-round IPM programs help you do this by ensuring you're applying pesticides only when you need to, and providing you with information so you can choose the most effective pesticide with the least harm to water quality, air quality, natural enemies, and honey bees.
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/span>- Author: Surendra K. Dara
Some Santa Maria strawberry growers experienced heavy infestations of whiteflies last year and there are already reports of infestations in some fields this year. Greenhouse whitefly, Trialeurodes vaporariorum has been a common strawberry pest in California for the past few years occasionally reaching high infestation levels that require targeted treatments. It used to be a concern mainly in the Oxnard area. Presence of the cut-back strawberries for second year production aid prolonged presence of whiteflies in the area and contribute to the early season infestations in new plantings.
Life stages of the greenhouse whitefly: Eggs darken when they are close to hatching. First instar nymphs are mobile and called crawlers. Later instars are immobile. Fourth instar nymphs are called pupae and characterized by long, waxy filaments. Adults have waxy, white wings. Black sooty mold grows on the honeydew secreted by whiteflies. (Photos by Jack Kelly Clark, Frank Zalom, and Surendra Dara)
Direct and indirect damage: Whitefly feeding affects plant growth and reduces yield and fruit quality. As they consume large quantities of plant sap, whiteflies excrete sticky honeydew deposited on the plant. Fungi of a few genera develop as black sooty mold on the honeydew covered surfaces. Sooty mold interferes with photosynthesis and affects plant growth. It also reduces the quality of the fruit.
Disease transmission: Greenhouse whiteflies are also important as vectors of pallidosis-related decline of strawberries. So, growers should be watching for symptoms of the disease which can be mistaken for nutritional deficiencies or abiotic disorders.
Pallidosis-related decline of strawberry is a viral disease caused by Strawberry pallidosis associated virus(SPaV) or Beet pseudo yellow virus(BPYV) along with non-whitefly transmitted viruses. Disease is not caused by SPaV or BPYV alone, but by the infection of SPaV or BPYV along with any of several non-whitefly transmitted viruses.
Symptoms of the disease include stunted plant growth, purple to red foliage, and brittle roots with reduced rootlets. Disease causes severe yield loss.
Whiteflies can cause a significant reduction in strawberry yield through direct feeding and indirectly through sooty mold and as viral disease vectors.
Biology: Greenhouse whitefly is about 1 mm long and has four membranous wings with white, powdery wax coating. Wings are held parallel to the top of the body. Eggs are small, elongated and attached to the lower leaf surface with a short pedicel. They are pale yellowish green to brown and turn dark with maturity. Eggs hatch and go through four nymphal instars before becoming adults. Immatures are oval, flat and often semitransparent. First instars are called crawlers which move around in search of ideal feeding sites on the underside of leaves. Later nymphal stages are immobile. Fourth instar nymphs are called pupa and have long, waxy lateral filaments and red eyes.
Management: Low population densities of whiteflies are usually controlled by the natural enemy complex in strawberries and pesticide treatments for other pests. Heavy infestations require timely treatments to prevent population build up. Monitor whitefly populations by using yellow sticky cards (1 per 10 acres) and counting their numbers on 20 mid-tier leaflets per each quarter of the field.
Refer to http://www.ipm.ucdavis.edu/PMG/r734301011.html for additional details on greenhouse whiteflies and their management.
My field trials: Among the control options that I evaluated, spiromesifen (Oberon) provided good control in a 2009 trial. In my 2012 large plot field trial, acetamiprid (Assail) alone at full label rate and acetamiprid at half the label rate along with the entomopathogenic fungus, Beauveria bassiana (BotaniGard 22 WP) provided a better control than other treatments.
2009 Trial: Percent change in whitefly populations two weeks after the treatment. *Note that spirotetramat is not registered for strawberries.
2012 Trial: Average percent change in whitefly populations after three applications. There was a general decline in their numbers throughout the experiment.