- Author: Surendra K. Dara
Western tarnished plant bug (Lygus hesperus), which is generally referred to as lygus bug, is a major pest of strawberries on the California Central Coast. Lygus bug feeding on developing berries causes fruit deformity. Deformed or ‘cat-faced' berries are not desirable for fresh market and lygus bug damage results in significant yield losses. Lygus bugs typically move into strawberry fields in early to mid-spring and thrive in fall-planted and summer-planted fields during the following months through multiple generations. Degree-day calculations and timing of treatments is difficult for lygus bug management in strawberries due to multiple sources (wild and cultivated hosts) and continuous movement of populations among different hosts. Conventional growers typically rely on pesticide applications and use of bug vacuums is gaining popularity in the recent years. Lygus bug management continues to be a challenge with these tools and emphasizes the need for IPM strategies that use several control options.
Studies conducted in 2012, 2013, and 2014 in commercial Santa Maria strawberry fields showed that non-chemical alternatives such as azadirachtin, entomopathogenic fungi, and bacteria-based pesticides can play an important role in managing lygus bug and other insect pests. Such botanical and microbial alternatives were also critical in managing twospotted spider mites. IPM approach beyond rotating chemicals among different modes of action groups is necessary for obtaining effective control, maintaining environmental sustainability, and reducing the risk of pesticide resistance.
An IPM study was conducted in 2015 at Sundance Berry Farms in the Santa Maria area using almost all available IPM tools. The following groups of options were used in different combinations and rotations and evaluated for their efficacy against lygus bug, western flower thrips, and greenhouse whitefly.
Chemical pesticides: Pyrethrins (formulations proprietary and Brigade, IRAC mode of action group 3A – sodium channel modulators), neonicotinoids [(formulation Assail 70 WP, IRAC group 4A), sulfoximines (formulation Sequoia, IRAC group 4C), and butenolides (formulation Sivanto, IRAC group 4D) – all of them are nocotinic acetylcholine receptor competitive modulators], flonicamid (formulation Beleaf 50 SG, IRAC group 9C – modulators of chordotonal organs), and benzoylureas (formulation Rimon 0.83 EC, IRAC group 15 – inhibitors of chitin biosynthesis).
Botanical pesticide: Azadirachtin (formulations cold pressed neem, Neemix, AzaGuard, and Debug Turbo), which is an insecticide, insect growth regulator, antifeedant, and a repellent.
Entomopathogenic fungi: Beauveria bassiana (formulation proprietary), Isaria fumosorosea (Pfr-97), and Metarhizium brunneum (Met 52 EC)
Mechanical: Vacuuming twice a week at one pass each time at 2 mph.
The study included 12 treatments that included an untreated control, Assail 70 WP alone and vacuuming alone as grower standards. Treatments were administered on 26 August, 2 and 9 September, 2015 using a tractor-mounted sprayer. A spray volume of 100 gpa was used for pesticide treatments. Each treatment had six 75' long (4 row) beds and four replications distributed in a randomized complete block design. Before the first treatment and 6 days after each treatment, 20 random plants from the middle two beds in each plant were sampled for insect pests and beneficial arthropods. Number of young and old nymphs, and adult lygus bugs, thrips, adult whiteflies, big-eyed bugs, minute pirate bugs, lace wings, damsel bugs, ladybeetles, parasitic wasps, predatory thrips, predatory midge larvae, and spiders were counted from each sample plant. Data were subjected to ANOVA and significant means were separated using Tukey's HSD test.
Pre-treatment and post-treatment (average of three counts) numbers of lygus bug nymphs and adults in different treatments.
Percent change in lygus bug (all life stages) and various natural enemy (all species combined) populations after three spray applications compared to pre-treatment counts
Ranking of the treatments based on percent change in lygus populations by the end of three spray applications
Percent change in western flower thrips and adult greenhouse whitefly populations after three spray applications compared to pre-treatment counts
Lygus bug: Lygus bug populations were very high during the study period (treatment threshold 1 nymph/20 plants) and control was difficult, in general. Sequoia/Sivanto/Belaf rotation provided the highest control where there was a 29% reduction in all life stages compared to pre-treatment numbers. Sivanto/Sivanto/Vacuum treatment was the only other treatment that provided a 12% control. B. bassiana+pyrethrum/Vacuum/Rimon+Brigade treatment prevented the population buildup and lygus numbers increased in all other treatments. The popular practice of vacuuming was ranked 6th. Having two passes instead of one pass might increase the efficacy of vacuuming, but results emphasize that multiple tools need to be considered for managing lygus bugs in strawberries.
Natural enemies: Percent change post-treatment indicated that natural enemy populations were relatively higher in Pfr-97+Neemix/Pfr-97+Neemix/Vacuum followed by Sequoia/Sivanto/Beleaf, and Sequoia/Sequoia/Vacuum and B. bassiana+neem/B. bassiana+pyrethrum+neem/B. bassiana+pyrethrum.
Western flower thrips: Post-treatment counts showed that thrips populations were reduced only in Rimon+Brigade/Met52+Debug Turbo/Met52+AzaGuard and B. bassiana+neem/B. bassiana+pyrethrum+neem/B. bassiana+pyrethrum treatments.
Greenhouse whitefly: Adult whiteflies occurred at very low numbers during the study and population reduction from post-treatment counts was seen only in Vacuum/Sivanto+Debug Trubo/Rimon+Brigade, Sivanto/Sivanto/Vacuum, and Rimon+Brigade/Met52+Debug Turbo/Met52+AzaGuard treatments.
This study demonstrates the efficacy of various chemical and non-chemical tools in various combinations against lygus bug, western flower thrips, and greenhouse whitefly and growers can make appropriate treatment decisions based on these results.
Acknowledgements: Thanks to Dave Murray for collaborations with this study, Ted Ponce for coordination, Sundance Berry Farms crew, Chris Martinez, Fritz Light, Tamas Zold, and Kristin Nicole Stegeman for their technical assistance, and industry partners for the supply of materials and/or financial support.
- Author: Surendra K. Dara
Lygus bug nymphal and adult stages
Lygus bug or western tarnished plant bug (Lygus hesperus) is a major pest in California strawberries and causes significant yield losses by contributing to the fruit deformity. Lygus bug is a hemipteran insect and has piercing and sucking mouthparts. They prefer plant parts rich in proteins and lipids. Developing berries and achenes offer as a good source of nutrition in strawberries and hence they are normally seen in the inflorescence. When lygus bug inserts its mouth parts and sucks the plant juices, the tissue at the site of feeding does not grow normally resulting in fruit deformity as berries develop. Deformed berries are not marketable for fresh market and growers adopt various control strategies to manage lygus bugs and limit damage. Chemical pesticides are the popular choice for managing lygus bugs and the use of bug vacuums is also increasing in the recent years.
While the treatment threshold is one lygus nymph/20 plants, infestations are generally very high above the threshold requiring aggressive management practices. Although treatment decisions are typically made based on lygus sampling, it is not uncommon (based on personal communication with some growers and PCAs) for fruit deformity to influence treatment decisions. In light of this scenario, it is important to determine the role of lygus bug in deformed strawberries among other causes such as poor pollination, genetic factors, and environmental conditions such as cold temperatures.
Literature suggests that fruit deformity due to lygus and other causes can be determined by the size of achenes (Zalom et al., 2014). Achenes in the deformed and normal areas of the fruit are more or less of the uniform size if the deformity is due to lygus bug. Achenes are of different sizes if the deformity is due to factors other than lygus damage.
A study was conducted in September, 2015 to evaluate the role of lygus bug and other factors in strawberry fruit deformity. Deformed berries were collected from 18 conventional and 10 organic strawberry fields. Conventional fields were sampled nine times and organic fields were sampled 5 times. On each sampling date a field block was divided into four quadrants and at least 100 deformed berries were collected from each quadrant. Each berry was examined categorized as lygus- and non-lygus-related based on the size of the achenes and shape of the berry. Data were subjected arcsine transformation and statistical analysis and significant means were separated using Tukey's HSD test.
In general, lygus bug damage was significantly higher (P = 0.0002) in organic fields than in conventional fields. When the causes for the deformity were compared, the proportion of deformed berries due to lygus bug damage was significantly higher (P < 0.00001) than those due to other causes in both conventional and organic fields. It is, however, important to note that 41% of the deformity in conventional fields and 33% in organic fields was due to factors other than lygus bug. These results are important in understanding the role of various lygus bug and other factors in causing fruit deformity and making appropriate treatment decisions. Sampling the fields for lygus bugs is always the right way to make a treatment decision rather than counting on deformed berries.
Information on lygus bug biology, sampling, and management can be found at the following resources:
Lygus bug biology and damage video: www.youtube.com/watch?v=7sZu9nirOPQ
Lygus bug monitoring and treatment threshold video: https://www.youtube.com/watch?v=Z7o7fafxuhE
Lygus bug management video: https://www.youtube.com/watch?v=5-4qcvceqmU
UC IPM Pest Management Guidelines: http://www.ipm.ucdavis.edu/PMG/r734300111.html
http://ucanr.edu/articlefeedback
Reference
Zalom, F. G., M. P. Bolda, S. K. Dara, and S. Joseph (Insects and Mites). 2014. UC IPM Pest Management Guidelines: Strawberry. University of California Statewide Integrated Pest Management Program. Oakland: UC ANR Publication 3468. June, 2014.
/span>- Author: Surendra K. Dara
Strawberry is an important commodity in California with a crop value of $2 billion (NASS, 2013). Lygus bug or western tarnished plant bug (Lygus hesperus), twospotted spider mite (Tetranychus urticae), greenhouse whitefly (Trialeurodes vaporariorum), and western flower thrips (Frankliniella occidentalis) are considered as important arthropod pests of strawberries which can cause significant yield losses. According to the Pesticide Use Report of California Department of Pesticide Regulation (2014), more than 200,000 lb of chemical insecticide and miticide active ingredients were used in strawberries in 2012. Among the 50,000 lb of biorational active ingredients that were additionally applied, 97% were Bacillus thuringiensis products used against lepidopteran pests. Apart from the release of various species of predatory mites against twospotted spider mites, pest management in strawberries is mainly dependent on chemical pesticides and IPM is generally limited to the rotation of pesticides in different modes of action groups.
In an effort to develop an effective IPM program with a particular emphasis on lygus bug management, research has been conducted for the past few years in Santa Maria to evaluate the role of various non-chemical alternatives. Field studies in 2013 showed that botanical and microbial pesticides can be effectively used in combination and rotation with chemical pesticides (Dara, 2014). Additional studies were conducted in 2014 to evaluate the efficacy of various combinations and rotations of new and existing chemical pesticides along with botanical, earth-based, and microbial pesticides.
Methodology
A large scale field study was conducted during June and July, 2014 in a conventional strawberry field of variety Del Rey at Goodwin Berry Farms, Santa Maria. Chemical pesticides included those from IRAC mode of action groups 3A (sodium channel modulators) 4A (neonicotinoids), 4C (sulfoximines), 6 (chloride channel activators), 9C (selective homopteran feeding blockers), and 15 (inhibitors of chitin biosynthesis). Additionally, diatomaceous earth, azadirachtin, and two entomopathogenic fungi, Beauveria bassiana and Metarhizium brunneum (formerly known as M. anisopliae) were also used. Diatomaceous earth is a powder form of fossilized remains of diatoms and contains silicon dioxide as an active ingredient. Silicon dioxide interferes with the integrity of the cuticle by absorbing the waxy layer and causes mortality due to desiccation. Both B. bassiana and M. brunneum are soilborne entomopathogenic fungi which cause infection when a conidiospore comes in contact with an insect or a mite. Azadirachtin, a secondary metabolite present in neem seed, is a limonoid compound which interferes with the synthesis of various proteins and thus affects molting, mating, sexual communication, and reproductive ability. It also has insecticidal properties and acts as an antifeedant and repellent. Using these alternatives can help pest management which is sometimes difficult to achieve with chemical pesticides alone.
Treatments included an untreated control, a wettable powder formulation of acetamiprid as the grower standard, and other materials in different combinations and rotations (Tables 1 and 2). Each plot had seven 75' long and 64” wide beds and treatments were replicated four times in a randomized complete block design. Treatments were administered late afternoon or in the evening using a tractor-mounted sprayer except for diatomaceous earth dust which was applied by a backpack dust applicator. Three applications were made at 7-8 day intervals and observations were made once before the first application and 5-6 days after each application. On each observation date, 20 plants were randomly sampled from the middle three beds of each plot by gently beating the plant to dislodge insects into a container. The number of aphids, lygus bugs (young and mature nymphs and adults), thrips, whitefly adults, and various species of natural enemies were counted from each plant. Natural enemy complex included bigeyed bug (Geocoris spp.), minute pirate bug (Orius spp.), lacewing (Chrysoperla spp. and Chrysopa spp.), damsel bug (Nabis spp.), lady beetle (multiple species), parasitoids (multiple species), and spiders (multiple species). Data were analyzed using statistical procedures.
Table 1. List of treatments used in this study and their application rates per acre – Active ingredients
*3A Sodium channel modulators 4A Neonecotinoids, 4C Sulfoxamines, 6 Chloride channel activators, 9C Selective homopteran feeding blockers, and 15 Inhibitors of chitin biosynthesis.
Table 2. List of treatments used in this study and their application rates per acre – Trade names
*3A Sodium channel modulators 4A Neonecotinoids, 4C Sulfoxamines, 6 Chloride channel activators, 9C Selective homopteran feeding blockers, and 15 Inhibitors of chitin biosynthesis.
Results and Discussion
Actual numbers of various pests and natural enemies are presented in Table 3 and percent change post-treatment compared to pre-treatment is presented in different figures.
Table 3. Pest and natural enemy populations from various treatments before and after treatment per 20 sample plants. Post-treatment counts include averages for three spray applications. Refer to Tables 1 and 2 for the list of treatments.
Aphid: Negligible number of aphids was seen only in few treatments and data are not presented.
Lygus bug: Lygus numbers increased in all treatments after treatment and there were no statistical differences (P > 0.05). However, when the percent change, compared to pre-treatment counts, was considered, some treatments appeared to be more effective than others in preventing population buildup. The high rate of Sequoia (treatment 8) limited the increase to 14% followed by the rotation of Diafil high rate-BotaniGard low rate+Assail 70 WP-Met 52+Molt-X (treatment 12) indicating the potential of non-chemical alternatives for lygus bug management (Table 4). When BotaniGard+Molt-X combination was applied twice after Rimon+Brigade combination (treatment 4), it appeared to be the fourth best rotation limiting the population build up to 54%. Untreated control and Assail 70 WP had the highest lygus numbers with 383% and 1083% increase, respectively.
Percent change in all stages of lygus bugs after three spray applications.
Treatments ranked according to their efficacy as expressed by the percent change/control of lygus bugs after three spray applications.
Thrips:There was a general reduction in thrips numbers post-treatment. There was a 48% reduction in their post-treatment numbers in untreated control while it varied from 35% treatment 2 to 68% in treatment 12.
Percent change in western flower thrips populations after three spray applications.
Whitefly adult:Most of the treatments reduced whitefly populations except for one treatment where there was a 20% increase (treatment 11 – Diafil low rate followed by Sequoia low rate+Molt-X, and Met 52) compared to a 13% in untreated control. There was a 7 to 78% reduction in whitefly populations in all other treatments.
Percent change in greenhouse whitefly adult populations after three spray applications.
Natural enemy complex:The number of big-eyed bug, parasitoids, and spiders significantly varied among various treatments post-treatment (P < 0.05, data not shown). When the percent change was considered for the entire natural enemy complex, there was a reduction in all treatments with 41% reduction in untreated control and 53-86% reduction in various treatments.
Diafil application left a white deposit on strawberry plants for several days making the berries unmarketable. It may not be practical for managing lygus bug, which usually appears after fruit production starts.
These results support last year's data in demonstrating the potential of non-chemical alternatives such as microbial and botanical pesticides. These tools are essential for sustainable pest management and can make a significant reduction in chemical pesticide use without compromising the control efficacy.
http://ucanr.edu/articlefeedback
References
California Department of Pesticide Regulation. 2014. Summary of pesticide use report data 2012: Indexed by commodity.
Dara, S. K. 2014. New strawberry IPM studies with chemical, botanical, and microbial solutions. CAPCA Adviser 17: 35-37.
National Agricultural Statistics Service (NASS) 2013. California agricultural statistics: 2012 crop year.
- Author: Surendra K. Dara
The western tarnished plant bug or lygus bug (Lygus hesperus), the western flower thrips (Frankliniella occidentalis), the greenhouse whitefly (Trialeurodes vaporariorum), and the strawberry aphid (Chaetosiphon fragaefolii) are important insect pests of strawberries in California (Zalom et al., 2014). While the importance of thrips and whitefly fluctuates from year to year, lygus bug continues to be a major problem in strawberries.
Changing pest conditions have a potential for increased pesticide applications and possible resistance issues. There is a need to emphasize the importance of integrated pest management and explore alternatives to chemical pesticides. Previous field studies in Santa Maria demonstrated the potential of azadirachtin and the entomopathogenic fungus, Beauveria bassiana for managing strawberry pests, particularly the lygus bug when used as standalone treatments or in combination of other materials (Dara, 2013). Additional studies conducted in Santa Maria evaluated azadirachtin, B. bassiana, a biopesticide based on Chromobaterium subtsugae,and existing and newly registered chemicals in a rotation program. The objectives of this study were to determine the efficacy of new chemicals against lygus bug and to identify treatment combinations where good pest control can be achieved with non-chemical alternatives or reduced rates of chemicals.
Methodology
A large plot field study was conducted on strawberry variety, Virtue at Manzanita Berry Farms in Santa Maria which was planted on October 20, 2012. Existing and newly registered chemical active ingredients such as acetamiprid (Assail), bifenthrin (Brigade), bifenthrin+avermectin (Athena), flonicamid (Beleaf), novaluron (Rimon), piperonyl butoxide+pyrethrins (EverGreen), and sulfoxaflor (Sequoia) were evaluated along with non-chemical alternatives such as azadirachtin (Molt-X), B. bassiana (BotaniGard), and Chromobacterium subtsugae (strain PRAA4-I) (Grandevo) in a rotation program (Tables 1 and 2). Acetamiprid was used as a grower standard along with an untreated control. Although B. bassiana is infective to all life stages, some immature stages might escape infection by getting rid of the attached conidia during molting. The combination of azadirachtin and B. bassiana target immatures and adults, respectively, and could be compared to the combination of novaluron and bifenthrin. Using the lowest label rates of chemical active ingredients along with B. bassiana was intended to reduce the use of chemicals without compromising the control efficacy. Each treatment included seven 75' X 68” long beds replicated four times and arranged in a randomized complete block design. Treatments were applied by the grower using tractor-mounted spray equipment at 50 gallons per acre on 14, 22, and 29 May, 2013. The first application was made late afternoon and the remaining two during early morning hours. Non-ionic surfactant was used at 0.125% concentration for treatments that included B. bassiana and at 0.25% for all other treatments. Insect and natural enemy populations were monitored 5 or 6 days after each treatment by sampling 20 random plants in the middle three beds of each plot. Sample plants were gently beaten with the lid of a plastic container to dislodge arthropods and the number of aphids, lygus bugs, thrips, whiteflies, and various species of natural enemies in the container was counted. Natural enemies that were observed during the period included bigeyed bug (Geocoris spp.), minute pirate bug (Orius spp.), lacewing (Chrysoperla spp. and Chrysopa spp.), damsel bug (Nabis spp.), lady beetle (multiple species), parasitoids (multiple species), and spiders (multiple species). Data were analyzed using ANOVA and significant means were separated using Tukey's HSD test.
Table 1. List of treatments used in this study and their application rates per acre – Active ingredients
Table 2. List of treatments used in this study and their application rates per acre – Trade names
Results and discussion
Treatments varied in their efficacy against different pests when individual sampling dates (data not showed) and average for three sampling dates were considered (Table 3).
Table 3. Pest and natural enemy populations from various treatments before and after treatment per 20 sample plants. Post-treatment counts include averages for three spray applications. Refer to Tables 1 and 2 for the list of treatments.
Aphids: Very low numbers of aphid infestations occurred during the study period. Average number varied from 0 to 0.33/20 plants during the post-treatment period, but there was no statistically significant difference among different treatments (P > 0.05, data not shown).
Lygus bug:Lygus numbers were more or less similar initially and significant differences were seen after the 2nd and 3rd spray applications (P < 0.01). When the average for nymphal and adult stages for post-treatment period was considered, the lowest number was found in treatment 5 (two sprays of Rimon and Brigade followed by EverGreen) and treatment 10 (low rates of Assail, Beleaf, and Athena with BotaniGard) followed by treatments 11 (Sequoia at high rate, BotaniGard, and Grandevo) and 6 (Rimon+Brigade followed by two sprays of BotaniGard+Molt-X). The highest numbers were seen in untreated control and plots treated with Grandevo alone. When individual life stages were considered, there were no statistically significant differences in the number of 4th and 5th instar nymphs and adults post-treatment (P > 0.05). However, treatments 11, 5, 3 (two sprays of Beleaf followed by Athena), and 12 (two sprays of Sequoia at low rate followed by Beleaf) had the lowest number of 1st to 3rd instar nymphs (P < 0.0001).
When change in lygus populations as a result of treatments was considered, numbers increased in untreated control, treatments 7 (Grandevo), 8 (BotaniGard, Grandevo, and Beleaf), and 9 (two sprays of EverGreen followed by Assail). Following an increase after the first application, reduction in populations was seen in treatments 2 (Assail), 3, 4 (two sprays of Athena followed by Beleaf), and 12 after subsequent applications.
Percent change in lygus numbers (all life stages) after each spray application (above) and at the end of three spray applications (below)
Thrips:There was an increase in western flower thrips numbers after the first spray application. Treatments appeared to show their effect following the second application where the increase was limited. However, there was a general decline in their numbers in all plots after the third application. Number of thrips varied from 29 to 39 per 20 plants for post-treatment averages, but they were not statistically significant (P > 0.05).
Percent change in western flowerthrips after each spray application (above) and at the end of three spray applications (below)
Whiteflies: Low numbers of whiteflies were observed during the observation period. Pre-treatment whitefly counts were not available, but the number of adults for post-treatment period varied significantly among treatments (P = 0.03). The lowest number of whiteflies was seen in treatments 3, 10, and 12.
Natural enemies:There was a general decline in natural enemy populations in all plots after treatments were administered. Although highest numbers were seen in untreated control (P = 0.002), there was no specific trend on specific treatments that could be detrimental or beneficial to natural enemies.
This study showed the efficacy of several active ingredients against the primary target, lygus bug and other pest populations. Most of the treatments were effective in reducing lygus populations except for those that had Grandevo alone (treatment 7), BotaniGard+Molt-X followed by Grandevo, and Beleaf (treatment 8), and two EverGreen sprays followed by Assail (treatment 9). Substituting the combination of Rimon and Brigade combination with Molt-X and BotaniGardappeared to be an environmentally safe, but effective strategy to achieve good lygus control. Similarly, using reduced rates of Assail, Beleaf, and Athena with BotaniGard (treatment 10) also appeared to provide good control. Such non-chemical alternatives serve as an important part of resistance management and integrated pest management. Important aspects of insect resistance management addressed by this study include i) reducing the total number of chemical insecticide applications, ii) using lower rates of chemical pesticides, iii) rotating different modes of action, and iv) incorporating non-chemical alternatives. This study demonstrates the efficacy of existing and new chemistries as well as the potential of botanical and microbial control options for lygus bug management in strawberries. These results also underscore the role of non-chemical alternatives beyond organic agriculture and their potential in conventional cropping systems.
Acknowldegments: Thanks to Dave Peck, Manzanita Berry Farms for the collaboration and to the pesticide industry partners for funding the study. Thanks to Chris Martinez, Jacob Conway, and Maria Murrietta for their technical assistance.
http://ucanr.edu/articlefeedback
References:
Dara, S. 2013. Microbial control as an important component of strawberry IPM. February issue of CAPCA Adviser magazine.
Zalom, F. G., M. P. Bolda, S. K. Dara, and S. Joseph (Insects and Mites). 2014. UC IPM Pest Management Guidelines: Strawberry. University of California Statewide Integrated Pest Management Program. Oakland: UC ANR Publication 3468. June, 2014.
- Author: Surendra K. Dara
The western tarnished plant bug, Lygus hesperus has a wide host range and is an important pest of many crops. It is commonly referred to as lygus bug and is a major pest of strawberries on the California Central Coast. In the recent months, it has emerged as a major threat to celery causing significant yield losses which, in some cases, lead to a complete loss of the crop.
Lygus bug feeding causes fruit deformation in strawberry, but the damage is quite different in celery. Lygus bug punctures celery stalks with its piercing and sucking (needle-like) mouthparts to feed on plant juices. Damaged tissue results in brownish, sunken, elongated lesions. Such lesions are usually seen below the first node, but feeding of the nymphs (or adults) on the inner and developing parts can result in dark spots and twisted or distorted growth.
Nymphal instars and adult L. hesperus.
Lygus bug is a hemipteran pest (Family: Miridae) and prefers to feed on plant parts that are high in lipid and protein content such as developing seeds. Flowering weed hosts such as wild mustard and wild radish and cultivated crops such as alfalfa are among the favorite hosts of the lygus bug compared to strawberries or celery. However, when vegetation in the uncultivated areas dries out in late spring, lygus populations disperse in search of food and migrate to other crops. Intensive agriculture on the fertile and environmentally ideal Central Coast offers a never ending food source of a variety of crops to the lygus bug.
Drought and warmer conditions can dry up wild habitats and force the migration of lygus bug populations sooner than usual. Pests require less time to develop and complete their life cycle in warmer climate resulting in increased infestations. Cold temperatures during winter months typically reduce populations of several pests, but milder winters aided by an endless supply of food sources may also contribute to the carryover of lygus bug and other pests to the following season resulting in continuous and/or early infestations. Under these circumstances, using degree-day models or other such tools appear to be impractical in predicting lygus infestations.
Farms have boundaries, but pests do not have such limitations and freely move from one field to another. Effective pest management is thus necessary not only to limit damage to the infested fields, but also to limit the spread to other fields. In 2013, ineffective management of whiteflies on strawberries lead to their build up and resulted in the outbreak of an uncommon disease known as viral decline of strawberry (pallidosis-related decline). Increased outreach helped growers to take appropriate management decisions and reduce whitefly vector populations. Similarly, effective and timely management of lygus bug on strawberries or other hosts is very important to prevent their spread to other crops.
When a pest issue emerges, it is not uncommon to put an emphasis on chemical pesticides for bringing populations down to manageable levels. However, efficacy of various pesticides vary due to their modes of action and other factors and resistance of some populations make otherwise effective chemistries less efficacious. It is important to implement IPM strategies and use cultural, biological, botanical, chemical, microbial, and other options rather than relying on one or two options for managing lygus bug and other pests. When chemical pesticides are used, rotate among different modes of action groups to reduce the risk of resistance development.
According to the Santa Barbara County Ag Commissioner's office, failure to take timely actions to manage a pest that could become a major issue to the neighboring fields, can have legal implications.
Lygus bug management on strawberries and celery can be found at the following sources:
Strawberry:
- UC IPM: http://www.ipm.ucdavis.edu/PMG/r734300111.html
- 2012 Santa Maria Study: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9595
- 2013 Santa Maria Study: http://capca.com/assets/magazine/February2014/index.html#/34/
- 2014 Santa Maria Study: http://capca.com/assets/magazine/February2015/index.html#/40/
Celery:
- UC IPM: http://www.ipm.ucdavis.edu/PMG/r104300411.html
To know more about lygus bug management and recent IPM studies, attend the Annual Santa Maria Strawberry Meeting on 10 November, 2015 at the Santa Maria Library. Register at http://ucanr.edu/2015strawberrymeeting.