Grower Notes and Pest News
Can entomopathogenic fungus, Beauveria bassiana be used for pest management when fungicides are used for disease management?
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show the importance of these microbial pesticides in pest management on conventional farms (Dara 2013, 2014, and unpublished).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 EX) 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.
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.
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.
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)
Adult light brown apple moth (Photo by Jack Kelly Clark, UC IP)
Nursery workers are our first line of defense in detecting light brown apple moth when growing ornamental plants in commercial nurseries. A new brochure and video can help those in the field distinguish light brown apple moth from several look-alike caterpillars.
Light brown apple moth is currently under a California Department of Food and Agriculture quarantine that regulates the interstate shipment of plants to keep the moth from spreading to new areas. It has been quarantined in various counties throughout coastal California ranging from Mendocino to San Diego.
Light brown apple moth larva (Photo by Jack Kelly Clark)
Correct field identification of the light brown apple moth is the first step in containing the spread of this moth. Unfortunately several other leafroller caterpillars, including the orange tortrix, omnivorous leafroller, avocado leafroller, and apple pandemic moth, look similar to light brown apple moth caterpillars. This makes photo identification tools that can go into the field with workers, like the Field Identification Guide for Light Brown Apple Moth in California Nurseries, a useful resource for nursery workers.
The field guide was created by Steven Tjosvold, Neal Murray, University of California Cooperative Extension; Marc Epstein, Obediah Sage, California Department of Food and Agriculture; and Todd Gilligan, Colorado State University with the Statewide Integrated Pest Management Program (UC IPM).
An exotic and invasive pest from Australia, light brown apple moth has a host range of more than two thousand plants. It is a pest to a wide range of ornamental and agricultural crops, including caneberries, strawberries, citrus, stone fruit, apples, and grapes. The caterpillars eat leaves and buds, leading to weak or disfigured plants. They also can feed directly on fruit, causing the fruit to be unmarketable.
For more information on light brown apple moth and other leafrollers found in nurseries, see the UC Pest Management Guidelines for Floriculture and Nurseries.
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.
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.
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
Center for Watershed Sciences - UC Davis
Water use in California – Public Policy Institute of California
California harvest much smaller than normal across crops – The Sacramento Bee
In virtual mega-drought, California avoids defeat – Los Angeles Times
Female (top), male and female in compulation (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 counties in California on various host plants.
Biology, damage, and management of Bagrada bug
Voraz plaga ataca huertos y jardines
UC IPM Kiosk displaying information in Spanish. Photo by Karey Windbiel-Rojas.
National Hispanic Heritage Month (September 15 – October 15) celebrates the contributions, culture, and history of Hispanic and Latino Americans originating from Spain, Mexico, Puerto Rico, Central America, and South America. These Americans make up the largest minority group in the United States and represent a very important part of the UC Statewide IPM Program's audience.
In recognition of National Hispanic Heritage Month, we'd like to highlight several important resources available from UC IPM to help Spanish-speaking audiences manage pests and apply pesticides safely.
For our Spanish-speaking urban audiences, several short videos on common pests such as ants, spiders, snails, bed bugs, and mosquitoes are available as well as Quick Tips (Notas Breves) offering advice on many pest problems and information on using pesticides safely. There are also 16 touch-screen computer kiosks located in various locations around the state where users can find pest and pesticide information in English or Spanish.
For maintenance gardeners preparing to take the California Department of Pesticide Regulation's Pesticide Applicators exam in the category Q, UC IPM offers a study guide and free online training course in Spanish.
National Hispanic Heritage Month actually originated in 1968 as “Hispanic Heritage Week.” In 1988, it was expanded to an entire month-long event in order to include many important historical events such as the anniversary of independence of Mexico, Chile, and several Central American countries (Belize, Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua). It ends after Columbus Day.
For more on other pest management and pesticide safety information available, please see the UC IPM Web site.