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.
Green peach aphids on a potted strawberry plant
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
Impact of soil and foliar applications of B. bassiana on green peach aphids on strawberry plants
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.
Akello, J., Dubois, T., Coyne, D., Kyamanywa, S. 2008. Endophytic Beauveria bassiana in banan (Musa spp.) reduces banana weevil (Cosmopolites sordidus) fitness and damage. Crop Protection 27: 1437-1441.
Behie, S. W., Jones, S. J., Bidochka, M. J. 2015. Plant tissue localization of the endophytic insect pathogenic fungi Metarhizium and Beauveria. Fungal Ecology 13: 112-114.
Bing, L. A., Lewis, L. C. 1991. Suppression of Ostrinia nubilalis (Hubner) (Lepidoptera: Pyraliade) by entomopathogenic Beauveria bassiana(Balsamo) Vuillemin. Environ. Entomol. 20, 1207-1211.
California Department of Pesticide Regulation (CDPR). 2014. Summary of pesticide use report data 2012: Indexed by commodity.
Dara, S. K. 2013a. Strawberry IPM study 2013: managing insect pests with chemical, botanical, and microbial pesticides. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19290.
Dara, S. K. 2013b. Entomopathogenic fungus Beauveria bassiana promotes strawberry plant growth and health. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11624.
Dara, S. K. 2014. Strawberry IPM study 2014: managing insect pests with chemical, botanical, microbial, and other pesticides. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19294.
Dara, S. K. 2015. Strawberry IPM study 2015: managing insect pests with chemical, botanical, microbial, and mechanical control options. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19641.
Dara, S. K., Dara, S. R, Dara, S. S. 2013. Endophytic colonization and pest management potential of Beauveria bassiana in strawberries. J. Berry Res. 3: 203-211.
Dara, S. K., Dara, S. S., Dara, S. S. 2014. Entomopathogenic fungi as plant growth enhancers. 47th Annual Meeting of the Society for Invertebrate Pathology and International Congress on Invertebrate Pathology and Microbial Control, August 3-7, Mainz, Germany pp. 103-104.
Lewis, L. C., Berry, E. C., Obrycki, J. J., Bing, L. A. 1996. Aptness of insecticides (Bacillus thuringiensis and carbofuran) with endophytic Beauveria bassiana, in suppressing larval populations of the European corn borer. Agri. Eco. Environ. 57, 27-34.
Posada, F., Aime, M. C., Peterson, S. W., Aehner, S. A., Vega, F. E. 2007. Inoculation of coffee plants with the fungal entomopathogen Beauveria bassiana(Ascomycota: Hypocreales). Mycol. Res. 111: 748-757.
Tefera, T., Vidal, S. 2009. Effect of inoculation method and plant growth medium on endophytic colonization of sorghum by the entomopathogenic fungus Beauveria bassiana. BioCon. 54: 663-669.
Vega, F. E., Posada, F., Aime, M. C., Pava-Ripoll, M., Infante, F., Rehner, S. A. 2008. Entomopathogenic fungal endophytes. Biol. Con. 46: 72-82.
Wagner, B. L., Lewis, L. C. 2000. Colonization of corn, Zea mays, by the entomopathogenic fungus Beauveria bassiana. Appl. Environ. Microbiol. 2000: 3468-3473.
Zalom, F. G., Bolda, M. P., Dara, S. K., Joseph, S. 2014. UC IPM Pest Management Guidelines: Strawberry. University of California Statewide Integrated Pest Management Program. Oakland: UC ANR Publication 3468. June, 2014./span>
Lygus bug (Lygus hesperus) adult (above) and young nymph (below). (Photos by Rodney Cooper, USDA-ARS and Surendra Dara)
Lygus bug or the western tarnished plant bug, Lygus hesperus is a major pest of strawberries in California (Zalom et al. 2014). Lygus bug has a wide host range that includes more than 100 species of cultivated crops and wild host plants (Scott, 1977; Fye, 1980 and 1982; Mueller et al., 2005) that include cultivated crops such as alfalfa, broccoli, celery, cauliflower, grapes, strawberries, and tomatoes on the California Central Coast. Additionally, ornamental and vegetable crops in greenhouses or home gardens along with weedy hosts from Chenopodiacae, Compositae, and Cruciferae in vast uncultivated landscapes offer a continuous food supply for lygus bug throughout the year. Warmer and dryer conditions as experienced in the recent years can also contribute to increased lygus bug problems. Milder winters fail to bring down overwintering populations and drought conditions dry out wild hosts early in spring forcing lygus bugs to migrate to cultivated crops. Under these circumstances, timely monitoring and implementation of appropriate management practices is necessary to limit damage and spread of lygus bugs to other crops. Vegetable crops such as celery are reported to have an increased risk of lygus bug damage in recent years (Dara, 2015a).
Lygus bugs primarily feed on inflorescence and developing seeds. They can also feed on foliage by sucking plant sap, but seeds which are rich in protein and lipids are important for the reproductive success of lygus bugs. Depending on the crop and crop stage, lygus damage can result in bud and flower loss, blemishes on seeds, necrotic spots on stems, or deformity of the fruit. In strawberries, fruit deformity caused by lygus bug renders fresh berries unmarketable. However, nearly 1/3 of the fruit deformity in strawberries is caused by factors other than lygus bug (Dara, 2015b).
Strawberry fruit deformity likely from lygus bug feeding (Photo by Surendra Dara)
Lygus bugs typically move into strawberry or other cultivated crops from weedy hosts in the wild habitats in April. However, seasonal weather conditions can alter these typical patterns. In a typical fall planting of strawberries, three generations of lygus bugs can be seen. But summer-plantings, extended season for fall-plantings, or early planting of fall strawberries make the crop available almost throughout the year. Improper management of lygus or any pest can lead to increased problems in crops where the pest is not usually a problem.
While UC IPM guidelines provide details of lygus bug management in strawberries and celery, here are some important points for managing lygus bug in strawberries during and at the end of the fruit production season:
- Several species of predatory and parasitic arthropods provide natural control of lygus bug. Big-eyed bug (Geocoris spp.), damsel bug (Nabis spp.), minute pirate bug (Orius tristicolor), and multiple species of spiders are among the predacious arthropods. Parasitic wasps that attach eggs (Anaphes iole) and nymphs (Peristenus relictus) are commonly found in strawberries. Conserving natural enemies by providing flowering hosts as refuges and selecting chemicals that are less harmful can contribute to biological control.
- Manage weeds near and around strawberry fields that serve as sources of lygus bug infestations.
- Some studies suggest growing strips of alfalfa or flowering hosts that attract lygus bugs and managing them with pesticides or vacuuming. This practice requires close monitoring to prevent dispersal of lygus bugs to strawberries.
Chemical control and biopesticides:
- A variety of chemicals that belong to different mode of action groups are registered for lygus bug in strawberries. Select appropriate label rates to obtain desired control. Using surfactants and proper application techniques can improve control efficacy.
- Rotate chemicals from different mode of action groups to reduce the risk of resistance development.
- Use appropriate materials for appropriate life stages of the pest. For example, an insect growth regulator like novaluron (Rimon) is effective against nymphal stages. To control a mixed population of nymphs and adults, novaluron can be used with other insecticides. Botanical insect growth regulator like azadirachtin (e.g., AzaGuard, Debug Turbo, Molt-X, and Neemix), which also has insecticidal properties, can be used with chemical pesticides. Microbial pesticides based on insect pathogenic fungi such as Beauveria bassiana (BotaniGard), Isaria fumosorosea (Pfr-97), and Metarhizium brunneum (Met52) in combination with azadirachtin or chemical pesticides can also be used as a part of the lygus IPM program.
- Bug vacuums can help remove lygus bugs from strawberry plants. They are typically run twice a week at a speed of 2 mph. Improved design and increased number of passes each time can enhance the control efficacy. Vacuums may not be effective in removing all life stages of lygus bugs and may also remove beneficial arthropods.
Control specific to end of the season:
- Do not neglect managing lygus until the end of the fruit production. Negligence can lead to the spread of the pest to neighboring fields requiring aggressive management practices. Such a situation that demands additional pesticide applications can lead to insecticide resistance in the long run.
- Some growers indicated that sulfuric acid applied as soil amendment at the end of the season helped in controlling lygus bugs. This practice is, however, not recommended for lygus management.
Several IPM studies in the Santa Maria area with a focus on lygus bug management provide information on effective chemical and non-chemical options.
- 2012: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9595
- 2013: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19290
- 2014: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19294
- 2015: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19641
Dara, S. K. 2015a. Increasing risk of lygus bug damage to celery on the Central Coast. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19221)
Dara, S. K. 2015b. Role of lygus bug and other factors in strawberry fruit deformity. (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19630)
Fye, R. E. 1980. Weed sources of lygus bugs in the Yakima Valley and Columbia Basin in Washington. J. Econ. Entomol. 73: 469-473.
Fye, R. E. 1982. Weed hosts of the lygus (Heteroptera: Miridae) bug complex in Central Washington. J. Econ. Entomol. 75: 724-727.
Mueller, S. C., C. G. Summers, and P. B. Goodell. 2005. Composition of Lygus species found in selected agronomic crops and weeds in the San Joaquin Valley, California. Southwest. Entomlo. 30: 121-127.
Scott, D. R. 1977. An annotated list of host plants for L. hesperus Knight. Bulletin of the Entomological Society of America 23: 19-22.
Zalom, F. G., M. P. Bolda, S.K. Dara, and S. Joseph., 2014. UC IPM pest management guidelines: strawberry. University of Californi a Statewide Integrated Pest Management Program. Oakland: UC ANR Publication 3468.
Seal of IPM - a practical and sustainable crop production system
Arthropod pests or diseases cause a variety of damages to crops. Some by reducing plant vigor resulting in lesser yields and some by causing direct damage to the produce which can be unmarketable due to deformity, unpleasant taste, damaged tissue due to insect feeding, presence of insects and/or frass, decay due to secondary infections, and other factors. It is quite understandable when the produce is not accepted because of the taste or potential health risk. For example, citrus fruit with huanglongbing or citrus greening disease transmitted by Asian citrus psyllid gives a bitter taste to citrus juice. Navel orangeworm larvae bore into almonds and feed on the nut causing complete or partial damage and leave frass and cause fungal infections. Brown marmorated stink bug damage on fruits and vegetables change the texture and taste of the damaged area. Such damage certainly makes the produce unmarketable and applying pesticides or administering other control measures to prevent the damage is warranted.
Brown marmorated stink bug damage to apple (above - Photo by Chris Bergh, Virginia Tech) and navel orangeworm damage to almond (below - Photo by Jack Kelly Clark, UC IPM)
On the other hand, certain damage is only cosmetic with no reported change in taste or quality of the produce. One example would be fruit deformity caused by the lygus bug in strawberries. Strawberry is a high value fruit appreciated for its taste, shape, color, and flavor. Lygus bug feeding on young green berries results in uneven growth and deformity of mature berries. While there is no record of the impact of lygus damage on strawberry fruit quality, millions of pounds of pesticides are applied to control lygus bug or similar pests that cause cosmetic damage in strawberries and other crops.
Cosmetic damage to strawberry by lygus bug (Photo by Surendra Dara)
The preference of consumers for perfectly shaped fruits and vegetables creates a need for intensive pest management practices and results in associated financial and environmental costs. Since chemical pesticides are generally economical and effective tools to manage pests, they are widely used. The overuse of certain effective pesticides causes development of resistance in pest populations. This, in turn, leads to increased use of the same or other pesticides. Excessive use of chemical pesticides can have a harmful effect on beneficial arthropods resulting in secondary pest outbreaks. Organic agriculture is gaining popularity due to environmental and human health concerns from chemical pesticide use. “Organic agriculture produces products using methods that preserve the environment and avoid most synthetic materials, such as pesticides and antibiotics” according to USDA. But organic agriculture is not necessarily the only sustainable solution.
Before agricultural industrialization, there was a better balance between pests and their natural enemies (beneficial arthropods such as predators and parasitoids that attack pests). Once agriculture was industrialized, thousands of acres of monoculture now provide an unlimited supply of food for a variety of pests. When the natural balance is disrupted, natural enemies alone are not sufficient to manage pest populations. This is where an Integrated Pest Management (IPM) strategy plays an important role in bringing a sense of balance into pest management. IPM employs multiple tools that include selecting resistant varieties, modifying planting dates, changing irrigation and nutrient management practices, conserving or releasing natural enemies, applying chemical, botanical, and microbial pesticides, or using mechanical tools. Each of these tools contribute to reducing pest numbers, complement each other, and result in pest management in an environmentally sustainable manner.
Organic agriculture, on the other hand, relies on biopesticides instead of chemical pesticides, which can sometimes be less effective or slow in achieving desired control. For example, an effective chemical pesticide with a specific mode of action could kill pest populations within a few hours of application. However, using a biopesticide based on an insect-pathogenic microorganism like the bacterium Bacillus thuringiensis or the fungus Beauveria bassiana, can take a few days to allow the microorganism to infect and kill the pest. When pest numbers are low, non-chemical solutions may provide required control to minimize damage. However, with heavy pest infestations, chemical pesticides are often needed to provide timely control that prevents further buildup of pest populations and the resulting damage to crops.
Organic agriculture is expensive because of generally higher losses due to pests and higher cost of agronomic and pest management practices. Sometimes, ineffective control of pests on organic farms may result in their spread to neighboring fields and increase the risk of pest damage. Organic agriculture does not mean pesticide-free farming, and biopesticides used on organic farms also require safety guidelines similar to chemical pesticides used on conventional farms. Organic agriculture may require a higher number of pesticide sprays increasing the risk of exposure for workers. In some pest and disease situations in certain crops, organically registered products are not available and yield losses could be higher. Exporting organic produce, in light of exotic and invasive pests spreading to other areas, is also a challenge due to limited options for shipping organically produced pest-free fruits and vegetables.
Using cultural practices to reduce the risk of pest infestations and applying biopesticides when pest populations are low and chemical pesticides when populations are high can be components of an IPM strategy where multiple tools are exploited in a balanced manner. Combining and rotating chemical pesticides with non-chemical alternatives strengthens the effectiveness of IPM by providing desired control without the excessive use of chemicals. Chemical pesticides can be used during early stages of the crop growth while biopesticides can be used closer to harvest.
Considering the challenges and risks associated with organic agriculture and the practicality of IPM-based agriculture, a couple of ideas could be worth pursuing to maintain environmental and human health, reduce harmful chemicals, and ensure food security for the growing world population.
Acceptance of imperfect produce: When consumers are tolerant of imperfectly shaped fruits and vegetables with no health risk from pathogens or arthropod pests, a significant amount of pesticides of all kinds could be avoided. This would translate into saving millions of dollars otherwise spent on pesticides and their application costs, and money earned on selling otherwise unmarketable produce. This may also reduce the disposal of unpicked produce at the grocery stores. When consumers accept imperfect fruits or vegetables, the cost of produce, both to produce and purchase, could come down. I recently came across Imperfect Produce, a company that sells imperfect produce and End Food Waste, an organization that started the Ugly Fruit And Veg Campaign.
IPM: Considering the difficulty in ensuring food security exclusively through non-chemical agriculture for the growing world population (projected to be 9.6 billion by 2050), IPM is an effective, practical, and sustainable tool that uses a balanced approach. While organic agriculture is encouraged and supported, and there are several organizations that certify organic production around the world, IPM hasn't caught the attention of marketers yet. Perhaps a seal of IPM should be considered and promoted in the near future.
Organic certification agencies from around the world. Source organicguidemalaysia.com
Opinions expressed in this article are my own and based on my experience in IPM, microbial control, biological control, and from discussions with several growers and scientists.
Tomato bug on a tomato plant. Photo by Surendra Dara
The bug that is commonly referred to as the tomato bug might have been around for a while, but it was in the spring of 2014 that a homeowner in Goleta (Santa Barbara County) reported infestations and damage to tomatoes in their home garden for the first time. In August, 2015, an organic vegetable grower in the Lompoc area had severe tomato bug infestations in tomatoes and zucchini. In a tomato field intercropped with zucchini bugs were found on both hosts, but more on the younger zucchini plants which have developing flowers and fruits compared to mature tomato plants. This incidence suggests the potential of tomato becoming an important pest of vegetables in commercial fields and home gardens. In September, 2015, tomatoes and yellow squash plants at the University of California Davis vegetable garden also had moderate tomato bug infestations. Younger tomato plants in the Davis garden had more tomato bugs than the squash plants next to them.
More tomato bugs were seen on younger zucchini than on older tomato plants (above) while more bugs were seen on younger tomato than on older yellow squash plants (below) Photos by Surendra Dara
It appears that tomato bugs can infest multiple hosts other than tomatoes and probably have a preference for plants with actively growing flowers and fruits.
Tomato bugs on zucchini flowers. Feeding damage appears as depressed spots on the fruit.
A field study planned for managing tomato bugs on organic tomatoes and zucchini with several botanical and microbial pesticides could not be executed, but the grower reported effective control with Pyganic+OroBoost and Pyganic+DebugTurbo+OroBosst when they tried some products on their new zucchini plantings under hoop houses. Other treatments that included Entrust, Trilogy, Pyganic, and DebugTurbo did not appear to suppress tomato bug populations. This input from the grower can be useful until scientifically conducted field study results are available in the future.
It is not clear if tomato bug is emerging as a new vegetable pest in California or the warm and dry conditions in recent years are contributing to the secondary pest outbreaks. Considering significant yield losses caused due to organic zucchini in the Lompoc area, it is important for growers and PCAs to know about the pest so that tomato bug can be added to their monitoring program.
Information on tomato bug origin, biology, and damage can be found at: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14833.
There is some discrepancy about the identity of what is commonly referred to as the tomato bug. Entomological Society of America listed Engytatus modestus (Distant) as the tomato bug and it is referred to as such and considered as a biocontrol agent in some literature (Parrella et al., 1982). However, Nesidiocoris tenuis (Reuter) is referred to as the tomato bugn in other reports where it is considered as a pest (El-Dessouki et al., 1976, Santa Ana, 2015).
N. tenuis is generally considered a beneficial insect and Arnó et al. (2006) characterized the damage to tomato plants. This insect is considered as a potential predator for controlling the tomato borer, Tuta absoluta (Meyrick), which has emerged as a serious pest in Spain and other European countries (Urbaneja et al., 2008). Another study in Spain reported N. tenuis both as a predator and a pest (Calvo et al., 2009). As a predator, tomato bug caused a significant reduction in sweetpotato whitefly, Bemisia tabaci Gennadius, populations under greenhouse conditions, but also caused necrotic rings on the petioles of leaves.
Regardless of the taxonomic status, tomato bug can both be a predator of several arthropod pests and a pest of tomatoes, yellow squash, and zucchini. Since it can feed on insects and plants, it is considered zoophytophagous.
Arno´ J, C. Castañé, J. Riudavets, J. Roig, and R. Gabarra. 2006. Characterization of damage to tomato plants produced by the zoophytophagous predator Nesidiocoris tenuis. IOBC/ WPRS Bull 29:249–254
El-Dessouki, S. A., A. H. El-Kifl, and H. A. Helal. 1976. Life cycle, host plants and symptoms of damage of the tomato bug, Nesidiocoris tenuis Reut. (Hemiptera: Miridae), in Egypt. Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz 83: 204-220.
Parrella, M. P., K. L. Robb, G. D. Christie, and J. A. Bethke. 1982. Control of Liriomyza trifolii with biological agents and insect growth regulators. California Ag. 36: 17-19.
Santa Ana, R. 2015. Humans may be culprit in latest South Texas invasive insect problems. AgriLife Today, 14 September, 2015. (http://today.agrilife.org/2015/09/14/tomato-bug-invades-south-texas/)
Urbaneja, A., H. Montón, and O. Mollá. 2008. Suitability of the tomato borer Tuta absoluta as prey for Macrolophus pygmaeus and Nesidiocoris tenuis. J. Appl. Entomol. 4: 292-296.
Micro-sprinklers in strawberries. Photo by Surendra Dara
Strawberry is an important commercial crop in California primarily grown on the Central Coast in Watsonville, Santa Maria, and Oxnard production areas. Strawberry crop requires 24-29” of irrigation water for a typical production season based on fall plantings. Irrigation is primarily administered through drip tapes installed under plastic mulch during bed preparation. In addition to the drip irrigation throughout the crop life, supplemental irrigation through overhead aluminum sprinklers is administered during the first few weeks after transplanting. Overhead irrigation is practiced to leach out salts from the root zone and to support the establishment of new transplants. Strawberries are sensitive to salinity and this supplemental irrigation is believed to reduce or prevent salt injury. In the Oxnard area, overhead aluminum sprinkler irrigation is considered very important to prevent dry conditions which could result from Santa Ana winds. However, overhead aluminum sprinkler irrigation requires a significant amount of water and can be an inefficient system. Evaporation, limited surface area for water penetration due to plastic mulch on the beds, and potential run off are some of the disadvantages associated with this overhead sprinkler system.
Water is an important resource for growing plants and it has become scarce due to epic drought conditions in California. Conserving water through improved irrigation practices is a critical area for maintaining acreage of a lucrative commodity such as strawberry. Micro-sprinklers, which are commonly used in orchard systems could offer an efficient alternative to conventional aluminum sprinklers. Micro-sprinklers, established on strawberry beds, can deliver water in a more targeted manner with minimum or no run off. They could also help modify the microclimate in the strawberry canopy and create humid conditions that discourage spider mite pest populations and promote predatory mites which are sensitive to dry conditions.
A study was conducted at Manzanita Berry Farms in Santa Maria during 2014-2015 production season to evaluate the potential of micro-sprinklers in strawberry production. Objectives of this study included i) conservation of irrigation resources without affecting strawberry plant growth and fruit yield, ii) impact on pest and predatory mite populations, and iii) impact on powdery mildew and botrytis fruit rot.
A block of strawberry (variety BG-6.3024 planted on 6 November, 2014) was divided into two parts with beds aligned from south to north direction. The west half of the block was assigned for micro-sprinklers and the east half for the grower standard with aluminum sprinklers. Each block had about 60 beds (about 306-365' long) and aluminum sprinklers were established in furrows every 40' (7-8 beds in between) while micro-sprinklers were established on every third bed. Micro-sprinklers were placed 16' apart (on every fourth bed) and had a 15' spacing within a bed. Within each treatment section six 20' long plots were marked to measure plant, pest, and disease parameters.
Installing micro-sprinkler system (Field crew at Manzanita Berry Farms, Santa Maria)
Micro-sprinkler (left) and grower standard with aluminum sprinklers (right) sections of the field
Data collection and results
Irrigation – Conventional sprinkler irrigation was made 14 times from 6 to 29 November, 2015 at a rate of 125 gallons per minute while micro-sprinkler irrigation was made 1-3 day interval at a rate of 40 gallons per minute using 35 PSI pressure. During this period, aluminum sprinklers delivered 120,000 gallons of water over 16 hours of total irrigation while micro-sprinklers delivered 81,600 over 34 hours of total irrigation. This translates to 32% of water saving in just 3 weeks and could be more in situations where overhead irrigation is administered for extended periods. Micro-sprinkler irrigation was continued for 15 min twice a week for the rest of the production period. Distribution uniformity could not be measured in grower standard treatment in this study, but it is believed to be between 50-60% at 70 PSI based on other studies. Distribution uniformity for the micro-sprinklers was 74% at 35 PSI when measured on 16 January, 2015. When electrical conductivity (EC) was measured on January 1 and February 1, 2015, it varied between 0.47 and 0.49 dS/m in grower standard treatment and was at 0.54 dS/m in micro-sprinkler treatment. Although EC in micro-sprinkler plots was significantly higher (P < 0.0007) than in grower standard plots, it was within the safe limit of 0.7 dS/m.
Cumulative volume of water delivered in micro-sprinkler and grower standard sections of the field. There was a saving of 38,400 gallons per acre in just about three weeks.
Yield – Total and marketable berry yield data were collected 2-3 times a week between 7 February and 12 June, 2015 for a total of 34 sampling dates. There was no significant difference in total or marketable berries (P > 0.05) when the seasonal averages for grower standard and micro-sprinkler plots were compared. During the observation period, 44,322 gr (97.7 lb) and 43,452 gr (95.8 lb) of marketable berries/plot were produced in grower standard and micro-sprinkler treatments, respectively.
Plots were covered with netting for exclusive harvest data collection.
Marketable berry yields per plot in micro-sprinkler and grower standard sections from February to June, 2015
Total strawberry yields (marketable and unmarketable) per plot during the study period.
Plant canopy and health– Growth was recorded by measuring the width of the plant canopy across and along the bed from 20 random plants per plot on the 6th of each month from January to March, 2015. Plant health was monitored at the same time by on a scale of 0 to 5 where 0 = dead, 1 = weak, 2 = moderate-low, 3 = moderate-high, 4 = good, and 5 = very good. Plants in micro-sprinkler treatment had significantly smaller canopy in January (P = 0.004) and February (P =0.0006), but caught up with the grower standard by March (P = 0.14). Plant health rating during this period also followed a similar trend, but the differences were significant only in February (P = 0.02).
Size of the plant canopy and plant health condition from January to March, 2015.
Both micro-sprinkler and grower standard plants look equally healthy and productive (Photo taken on 26 May, 2015)
Twospotted spider mite and predatory mite – One mid-tier leaflet was sampled from each of the 10 random plants within each plot and the number of eggs, nymphs, adult pest and predatory mites were counted using a mite brushing machine. Sampling was made once a month from February to April, 2015, but due to sparse numbers and uneven distribution useful data could not be obtained.
Powdery mildew– One trifoliate leaf from 20 random plants within each plot were collected and checked under microscope for mycelial growth and powdery mildew severity was rated on a 0 to 4 scale where 0 = absent, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, and 4 = 76-100% of leaf area with infection. Sampling was made on 15 April and 16 and 24 June, 2015. Powdery mildew severity was significantly less in micro-sprinkler treatment on 15 April (P = 0.009) and June 24 (P = 0.01).
Severity of powdery mildew on three observation dates.
Botrytis fruit rot – Berries harvested from each plot were kept at room temperature in plastic clamshell boxes and disease severity was measured 3 and 5 days after harvest using the 0 to 4 scale used for powdery mildew. Observations were made on 26 March, 13 April, 22 May, and 16 June, 2015. In general, botrytis fruit was less severe in micro-sprinkler treatment, but significant difference were seen 3 days after harvest for samples collected on 22 May and 16 June (P = 0.02).
Severity of botrytis fruit rot when observations were taken 3 and 5 days after harvest.
Micro-sprinkler system contributed to a significant reduction in overhead irrigation water without affecting the marketable berry yield. With less pressure required to deliver water through micro-sprinklers, they could also contribute to energy savings. EC value of below 0.7 dS/m suggests that micro-sprinklers were as effective as aluminum sprinklers in leaching out salts. Due to the lack of sufficient mite infestations, the benefit of micro-sprinklers in spider mite management could not be determined. Data also suggest that powdery mildew and botrytis fruit rot could be reduced by micro-sprinklers, but additional studies are required to confirm these preliminary observations. An initial estimate by the vendor suggests that equipment and handling costs of the micro-sprinklers are more or less similar to those of the aluminum sprinklers.
Chris Martinez and rest of the field crew, Manzanita Berry Farms, Santa Maria after transplanting
Acknowledgements: Thanks to Dave Peck, Manzanita Berry Farms for his collaboration, Chris Martinez for his field assistance, Manzanita field crew for help with planting, irrigation, and yield data collection, Danilu Ramirez, Fritz Light, and Tamas Zold for their technical assistance, and RDO Water and Netafim for partial funding of the study.
Dara. S. K. 2012. Salt injury in strawberries. UCCE eNewsletter, Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=6820