Western tarnished plant bug (Lygus hesperus) killed by the entomopathogenic fungus, Beauveria bassiana (Photo by Surendra Dara)
Beneficial fungi such as Beauveria bassiana are pathogenic to insect and mite pests and are commercially available for use in organic and conventional farming. Field studies conducted on commercial strawberry farms with B. bassiana and another entomopathogenic fungus, Metarhizium brunneum show the importance of these microbial pesticides in pest management on conventional farms (Dara 2013, 2014, and unpublished). These studies can make a significant contribution to IPM practices by reducing chemical pesticide use without compromising the pest management efficiency.
In a cropping system where fungicides are frequently applied for managing various foliar diseases such as powdery mildew (caused by Podosphaera aphanis) and botrytis fruit rot (caused by Botrytis cinerea), the fate of a beneficial entomopathogenic fungus is always an important question. Evaluating the compatibility of various fungicides commonly used in strawberries with B. bassiana is necessary to understand the fungicide and beneficial fungus interactions. A series of studies were conducted to address this issue and to explore opportunities to evaluate their compatibility.
In 2012, six bioassays were conducted using fungicides Captan, Elevate, Microthiol Disperss, Pristine Quintec, Rally, and Switch and an organic formulation of B. bassiana (Mycotrol-O) (Dara and Dara, 2013). Mortality and/or infection caused in mealworm (Tenebrio molitor) larvae exposed to surfaces treated with B. bassiana and fungicide was used as a measure of compatibility between the fungicides and the beneficial fungus. Except for Elevate and Quintec, all other fungicides showed moderate to high level of inhibitory effect on the fungus. A follow up study with Pristine showed that increasing the application interval to 1 or 4 days improved the compatibility and resulted in 100% mortality of the mealworms from B. bassiana treatment. Another study was conducted where B. bassiana (BotaniGard ES) was applied 0 to 6 days after fungicides Pristine, Merivon, and Switch were applied (Dara et al. 2014). Switch seemed to have a higher negative impact on B. bassiana than Pristine and Merivon, in general, but the increase or decrease in mealworm mortality with increasing time interval between the fungicides and fungus was variable. Although these two studies indicated that increasing time interval could influence the compatibility of fungicides and B. bassiana,they were conducted only once and warranted additional replicated studies.
A new study was conducted from June to August, 2014 where eight fungicides that had different modes of action were applied at 0 to 6 day intervals to evaluate their impact on mealworm mortality caused by B. bassiana.
Treatment list
Untreated control
Positive control with BotaniGard ES® (B. bassiana)
BotaniGard ES applied 0,1, 2…6 days after treating with Captan.
BotaniGard ES applied 0,1, 2…6 days after treating with Pristine.
BotaniGard ES applied 0,1, 2…6 days after treating with Merivon.
BotaniGard ES applied 0,1, 2…6 days after treating with Microthiol Disperss.
BotaniGard ES applied 0,1, 2…6 days after treating with Rally.
BotaniGard ES applied 0,1, 2…6 days after treating with Rovral.
BotaniGard applied 0,1, 2…6 days after treating with Switch.
BotaniGard ES applied 0,1, 2…6 days after treating with Thiram.
Captan alone applied 0, 1, 2…6 days prior to the exposure.
Pristine alone applied 0, 1, 2…6 days prior to the exposure.
Merivon alone applied 0, 1, 2…6 days prior to the exposure.
Microthiol Disperss alone applied 0, 1, 2…6 days prior to the exposure.
Rally alone applied 0, 1, 2…6 days prior to the exposure.
Rovral alone applied 0, 1, 2…6 days prior to the exposure.
Switch alone applied 0, 1, 2…6 days prior to the exposure.
Thiram alone applied 0, 1, 2…6 days prior to the exposure.
Including the untreated control, there were a total of 114 treatments in each assay. Each treatment had 10 mealworms that were individually incubated in Plexiglas vials with a piece of carrot after a 24 hour exposure to a paper towel treated with B. bassiana, fungicide, or B. bassiana+fungicide applied at different time intervals. Mortality of the worms was observed daily for 6 days. Treatments of fungicides without B. bassiana were also included to see if they have any influence on the mortality of the worms. These assays were repeated three times using medium-sized mealworms purchased from a commercial supplier.
Results
None of the worms in untreated control died during the study. Except for six dead worms out 560 in fungicide only treatments in the first assay, there did not seem to be any impact of fungicides alone on the mortality of mealworms.
Among the fungicides tested, Captan (Mode of action group M4) and Thiram (Mode of action group M3) are the only ones that showed a significant negative impact on B. bassiana resulting in reduced mealworm mortality (Fig. 1, Table 1). Other fungicides had no or negligible impact on B. bassiana. When the average total mortality of the mealworms among different time intervals between B. bassiana and fungicides was considered, Captan caused about 57% reduction and Thiram caused 43% reduction in the efficacy of B. bassiana. Remaining fungicides caused only 0-2% of reduction in the efficacy of B. bassiana. Both Captan and Thiram are broad spectrum fungicide acting through multi-site contact and differ from others, except for Microthiol Disperss (Mode of action group M2), in their modes of action.
Time interval between B. bassiana and different fungicides did not seem to have any impact on the total mortality of mealworms. Although the total mortality caused by B. bassiana ranged from 30-57% in Captan and 33-77% in Thiram treatments at different time intervals, differences were not statistically significant (P > 0.05).
Fig. 1. Average total mortality of mealworms at different time intervals between B. bassiana and fungicides
Table 1. Total mortality caused by B. bassiana when fungicides were applied at different time intervals.
*Means followed by the same letter within each column are not statistically significant (Tukey's HSD P > 0.05). There was no significant difference in values within each row i.e., no difference in time intervals between B. bassiana and any of the fungicides.
This study shows that several of the fungicides commonly used in strawberries are compatible with B. bassiana. When B. bassiana is considered for pest management, Captan and Thiram should be avoided. Fungus-based microbial pesticides play an important role in conventional agriculture and understanding their interaction with fungicides helps with their effective use in pest management.
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References
Dara, S. 2013. Microbial control as an important component of strawberry IPM. February issue of CAPCA's Adviser magazine, pp 29-32.
Dara, S. 2014. New strawberry IPM studies with chemical, botanical, and microbial solutions. February issue of CAPCA Adviser magazine, pp 34-37.
Dara, S. and S.S.R. Dara. 2013. Compatibility of the entomopathogenic fungus, Beauveria bassiana with some fungicides commonly used in strawberries. Strawberries and Vegetables Newsletter (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9626)
Dara, S. S., S.S.R. Dara, and S. Dara. 2014. Optimal time intervals for using insect pathogenic Beauveria bassiana with fungicides. Central Coast Agriculture Highlights (http://cesantabarbara.ucanr.edu/newsletters/Central_Coast_Agriculture_Highlights50500.pdf)
- Author: Surendra Dara
Average annual precipitation in California is 200 million acre-feet, out of which 42% of water is used for agriculture while 11% is used in the urban areas (municipal and industrial users) and the remaining 47% by the environment (native vegetation, ground water, and oceans) (Doug Parker, personal communication). According to the National Drought Mitigation Center's Drought Monitor, 95% of California is currently in a severe to exceptional drought condition. Drought has impacted California agriculture in different ways in different regions. Depending on crop needs, geographic location, and availability of ground water, production of each crop is affected in one way or the other. Compared to the Central Valley which is affected most by the drought, agriculture on the Central Coast and Southern California is less affected according to a study conducted by the Center for Watershed Sciences at University of California Davis.
Water use in California (Source: Doug Parker, Director of California Institute for Water Resources and Water Strategic Initiative Leader)
Drought conditions in California as of October 16, 2014. Source: US Drought Monitor.
Some strawberry and vegetable growers in San Luis Obispo and Santa Barbara Counties were contacted recently to assess the current impact of drought. Their feedback helped to put together the following summary of the current status and recommendations to address drought conditions.
Strawberries
Strawberry growers continue to use available groundwater although with concern for future availability. Current impact of the drought on strawberries:
- Strawberries require 21-24 acre inches of water and rainfall accounts for 3-6 acre inches during normal rainfall years. Rainfall leaches salts away from the root zone while meeting irrigation needs. Compared to three years ago, it is estimated that there is up to a 10% increase in some salts, especially calcium and magnesium due to the current drought conditions. This could lead to 5-10% reduction in fruit yields, but severe salt injury could cause higher losses. Additionally, plants would be vulnerable to pests and diseases which could lead to further yield reduction.
- Strawberries are very sensitive to salinity and frequent irrigation is practiced to prevent the accumulation of salts in the root zone. Growers are aware of diminishing groundwater resources and are carefully monitoring water and salinity levels. Extra irrigation to push out salts from the root zone results in nutrient leaching.
- These practices are expected to continue as long as groundwater is available, but acreage could diminish if groundwater becomes unavailable.
Salt injury to strawberry plant (Photo by Surendra Dara)
Strategies to address drought conditions in strawberry production:
- Continue to monitor groundwater levels and provide irrigation to meet water needs as well as to leach out salts.
- Monitor health of plants and regularly scout for pests and diseases which might require more timely treatment actions than usual because plants are already under stress.
- Check nutrient levels in the soil and plant and compensate as needed if irrigation is causing nutrient loss.
- Modify leaching fractions based on salt levels and plant maturity to flush salts away from the root zone.
- Reconsider acreage planted based on groundwater availability to minimize losses.
Vegetables
Vegetable growers are experiencing the impact of drought conditions on their production and are currently relying on available groundwater.
- Water needs for vegetables vary from about 7 to 36 acre inches based on the crop and location. Rainfall during a normal season contributes up to 24 acre inches depending on the crop and season.
- Drought conditions resulted in increased salinity, which has caused 10-20% reduction in yields of some crops and a significant increase in pest and disease pressure. Some growers are managing without any yield losses.
- Some growers have already reduced their acreage by 10% or more while others continue to maintain the current acreage.
- Reducing or completely avoiding pre-irrigation is currently practiced by some growers to cope with water shortage. This practice has also increased salinity in the soil and increased weed populations.
- Some growers have reduced fertilizers or are choosing ones with less salt content.
- In order to monitor salinity and nutrient levels, additional expenses are incurred for water, soil, and plant analysis. Increased weed, pest, and disease problems have also increased management costs.
- Some growers are prepared to reduce acreage up to 25% if drought conditions continue.
Strategies to address drought conditions in vegetable production:
- Continue regular monitoring of groundwater levels, salinity conditions, nutrient status, and provide irrigation and fertilizers as appropriate.
- Regularly monitor for pests and diseases and make timely management decisions.
- Reduce or avoid sprinkler irrigation and use drip irrigation as much as possible.
- Continue to reduce or avoid pre-irrigation to conserve water.
- Modify leaching fractions based on the current salt and crop conditions and administer irrigation as needed.
- Modify acreage to suit future water availability.
My current research is evaluating the potential of entomopathogenic fungi in improving water and nutrient absorption by plants, which could play a role in conserving water resources.
Acknowledgements: Thanks to the strawberry and vegetable growers in San Luis Obispo and Santa Barbara Counties who responded to the survey on drought impact and provided their valuable feedback.
UC and other resources:
California agriculture faces greatest water loss ever – College of Agricultural and Environmental Science, UC Davis
California Institute for Water Resources – UC ANR
Center for Watershed Sciences - UC Davis
Water use in California – Public Policy Institute of California
News articles:
California harvest much smaller than normal across crops – The Sacramento Bee
Drought highlights need for more outreach, education - Ag Alert
In virtual mega-drought, California avoids defeat – Los Angeles Times
- Author: Surendra Dara
Female (top), male and female in copulation (middle) and a mature nymph (bottom) of Bagrada bug on a dime. (Photo by Surendra Dara)
Bagrada bug (Bagrada hilaris) is an invasive pest that was first reported in California in 2008 in Los Angeles County. It is currently reported from the following 27 counties in California on various host plants.
Alameda
Amador
Butte
Contra Costa
Fresno
Imperial
Inyo
Kern
Kings
Los Angeles
Madera
Merced
Monterey
Orange
Riverside
Sacramento
San Benito
San Bernardino
San Diego
San Francisco
San Mateo
Santa Barbara
Santa Clara
Santa Cruz
Stanislaus
Ventura
Yolo
Videos:
Biology, damage, and management of Bagrada bug
Voraz plaga ataca huertos y jardines
Pest Alert: http://www.ipm.ucdavis.edu/pestalert/pabagradabug.html
Other articles:
1. Bagrada bug: An exotic pest in southern California
2. Bagrada bug is now in Santa Barbara County
3. Update on the Bagrada bug as it moves up to San Luis Obispo County
4. An update on the Bagrada bug
5. Bagrada bug host preference: Crucifers and green beans
6. Bagrada bug update: bioassays and a short video
7. Current distribution of Bagrada bug in California
/span>- Author: Surendra Dara
Bagrada bug [Bagrada hilaris (Burmeister)] is an invasive hemipteran insect (Family: Pentatomidae) that was first reported in Los Angeles County, California in 2008. It has now spread to several counties in California and is moving northwards.
Distribution: Citizen scientists have been instrumental in reporting the occurrence of Bagrada in various counties and are helping map its current distribution. As of September 2014, Bagrada bug is known to be present in Imperial, San Diego, Orange, Riverside, Los Angeles, San Bernardino, Kern, Kings, Inyso, Fresno, Merced, Ventura, Santa Barbara, Monterey, San Benito, Santa Cruz, San Mateo, Santa Clara, Alameda and Yolo Counties and is likely to be present in some other.
Distribution of Bagrada bug in various California counties as of September, 2014.
Bagrada bug is also spreading eastwards from California and is currently reported in Nevada, Arizona, Utah, New Mexico, and Texas.
Host plants affected: While Bagrada bugs are known to feed on a variety of host plants in addition to their preferred cruciferous hosts, serious damage to barley, carrot, corn, pepper, potato, tomato, and sunflower was recently reported by growers or gardeners. In a previous study where multiple food sources were offered, Bagrada bugs did not feed on tomatoes. They were also found on strawberries and reported to be present on other hosts, but damage has not been confirmed. Bagrada bugs might have been present on these plants as they move around in search of suitable food sources.
Damage to carrots from Bagrada bug feeding. (Photo by Rick Machado, Menifee)
Stippling and eventual necrosis of damaged tissue in chiko burdock. (Photo by Don DeLano, Pomona)
Backyard corn damaged by Bagrada bugs. (Photo by Larry Adcock, Arroyo Grande)
Adult Bagrada bugs on damaged pepper leaves. (Photo by Rick Machado, Menifee)
Seriously damaged seed potato plants (above) and tubers (below). (Photo by Rick Machado, Menifee)
Bagrada bug damage to sepals on sunflower. (Photo by Larry Adcock, Arroyo Grande)
Bagrada bug feeding damage to tomatoes. (Photos by Rick Machado, Menifee, above and Jennifer Evangelista, San Luis Obispo, below)
Bagrada bugs on strawberry foliage. Not seen to cause any feeding damage. (Photo by Jennifer Evangelista, San Luis Obispo)
Management: Regular monitoring, mechanical exclusion or removal, destruction of weed hosts, and chemical, botanical, and microbial pesticides continue to be available management options. There have been several queries in the past two months from home owners, community garden operators, and organic growers about serious Bagrada bug infestations. Avoiding cruciferous and other hosts at risk should be a serious consideration for community and home gardens where using some of the currently available management options is difficult.
What to do: If you see Bagrada bug in an area or on a host that is not previously reported, please contact Surendra Dara at skdara@ucanr.edu or 805-781-5940. This information will be useful to track the distribution of this pest.
Additional information:
Biology, damage, and control video: www.youtube.com/watch?v=gSj3AZoJIRM
Biology, damage, and control: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4047
Potential organic solutions: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11031
Host preference: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9611
General information: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=8438
- Author: Surendra Dara
Adult tomato bug (Cyrtopeltis modesta) on backyard tomato plant. See its slender, greenish body and needle-like mouthparts. (Photo by Jessie Altstatt, Goleta)
A homeowner in Goleta recently reported severe infestation and damage of tomatoes by the tomato bug, Cyrtopeltis modesta (Distant) in their home garden. It also appears that they have become more frequent in recent years. This article provides an overview of the pest and some management options.
Tomato bug also known as tomato suck bug belongs to the family Miridae in the order Hemiptera. Lygus bug and other plant bugs also belong to the same family. There seems to be some confusion in the description of C. modesta (Engytatus modestus) and without a good key, identification of related species such as C. tenuis, C. geniculata, and Dicyphus spp. can be complicated.
Origin and distribution: Origin of C. modesta was not clear in literature, but Carvalho and Usinger (1960) referred to it as an American species while reporting a new species of Cyrtopeltis from Hawaii. Tomato bug is reported from Europe, South America, and North America and its related species from other parts of the world.
Biology and identification:
Adults are 7-8 mm or 0.25” long. Body is slender, pale and has a green or red tinge. Pronotum (shield like plate on the thorax) is narrow. Eyes are small. Wings are membranous, pale green or translucent. Nymphs look similar to adults, but without wings or with developing wing pads. There are four to five nymphal instars. Eggs are laid inside the petiole or the terminal shoots. Nymphs and adults actively feed.
Adult (above) and nymphal stages (below) of tomato bug. Nymphs can be seen with no wings or developing wing pads. (Photos by Jessie Altstatt, Goleta)
Damage
Nymphs and adults actively feed by inserting their piercing and sucking mouthparts in plant tissues and sucking the juices. Yellowish red rings develop around the stem as a result of feeding. These areas are corky and break easily leading to the dropping off of flowers or developing fruit. Tomato bugs are common in Central Valley and Southern California both in organic and conventional tomatoes. However, they are usually not a problem in large farms where pesticides are applied to manage major tomato pests. They can be a problem in home gardens and small farms where pesticide treatments are less common (Tom Turini, personal communication).
Damaged leaves and flower from tomato bug feeding. (Photo by Jessie Altstatt, Goleta)
Management
There is no information available on natural enemies, pesticide treatments, or other management options specific to tomato bugs. Pesticides that are usually effective against lygus bugs (http://www.ipm.ucdavis.edu/PMG/r783301611.html) or stink bugs (http://www.ipm.ucdavis.edu/PMG/r783300211.html) in tomatoes can be effective against tomato bugs. Based on my research on other hemipterans, botanical insecticide/insect growth regulator – azadirachtin (especially against nymphal stages) and insect pathogenic fungi – Beauveria bassiana, Metarhizium brunneum (M. anisopliae), or Isaria fumosorosea (Paecilymyces fumosoroseus) can also be effective against tomato bugs. These could be good alternatives to chemical pesticides for home gardens.
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References
Carvalho, J.C.M. and R. L. Usinger. 1960.New Species of Cyrtopeltis from the Hawaiian Islands with a Revised Key (Hemiptera: Miridae). Proc. Hawaiian Entomol. Soc. 17: 249-254.
Goula, M. and O. Alomar. 1994. Míridos (Heteroptera Miridae) de interés en el control integrado de plagas en el tomate. Guía para su identificación. Bol. San. Veg. Plagas 20: 131-143.
Letourneau, D. K. and B. Goldstein. 2001. Pest damage and arthropod community structure in organic vs. conventional tomato production in California. J. Appl. Ecol. 38: 557-570.
Swezey, O. H. 1925. Notes and Exhibitions (Sept. 4, 1924). Proc. Haw. Ent. Soc, 6:18.
UC IPM http://www.ipm.ucdavis.edu/PMG/r783301811.html
University of Arizona http://ag.arizona.edu/ceac/sites/ag.arizona.edu.ceac/files/pls217nbCH4_3.pdf.
Taxonomic references:
http://zipcodezoo.com/Animals/C/Cyrtopeltis_modesta/
http://research.amnh.org/pbi/catalog/names.php?name_kwd=cyrtopeltis