- Author: Surendra K. Dara
Twospotted spider mite, Tetranychus urticae Koch is a major pest of strawberries in California. Spider mite damage reduces plant vigor and contributes to yield loss. Twospotted spider mites are typically found on the lower side of the leaf and form webbing at higher population levels.
Damage: Spider mites cause damage by puncturing the epidermis with their mouthparts and sucking the plant juices. Death of plant cells appears as yellow mottling during initial stages and as feeding continues, damaged areas coalesce and result in scarring, bronzing, and drying out of leaf tissue. This reduces the photosynthetic ability of the plant and thus its growth and vigor. If left uncontrolled, damage leads to stunted plant growth or eventual death. Damage symptoms are unique in Benicia variety where upper leaf surface corresponding to spider mite feeding on the lower side, shows purplish coloration.
Yellowing, scarring, bronzing, and drying of infested foliage and stunting of plants. (Photo by Surendra Dara)
Biology: Life cycle includes egg, larva, protonymph, deutonymph, and adult stages. Females lay an average of 100 eggs in 10 days. Eggs are round, initially translucent and turn whitish as they mature. Larvae have three pairs of legs and nymphal stages have four pairs of legs. Males are wedge-shaped and about 0.3 mm long. Females are oval, 0.4-0.5 long, and have a single dark spot on either side of their body. At 85-90 oF, life cycle can be completed in 7-8 days.
Life stages of twospotted spider mite (Photo by Surendra Dara)
Management: Growers typically rely on biological and chemical control options for managing twospotted spider mites in strawberries. Type I specialist Phytoseiulus persimilis Athias-Henriot, Type II specialists Neoseiulus fallacis (Garmin), N. californicus (McGregor), Galendromus occidentalis (Nesbitt), and Type III generalist Amblyseius andersoni (Chant) are common predatory mites that attack twospotted spider mites. Releasing one or more species of predatory mites is a popular practice in strawberry production. Abamectin, acequinocyl, bifenazate, etoxazole, fenbutatin-oxide, fenpyroximate, hexythiazox, and spiromesifen are the most commonly used chemical miticides according to pesticide use reports of the California Department of Pesticide Regulation. Chemical miticide use shows a 2% increase in the Watsonville-Salinas area, an 82% increase in the Santa Maria area, and a 125% increase in the Oxnard areas from 2009 to 2013. There is a continued need for identifying effective chemical and non-chemical miticides to manage twospotted spider mite in strawberries.
A small plot field study was conducted in 2013 at Manzanita Berry Farms in Santa Maria to evaluate the efficacy of various botanical, chemical, and microbial pesticides. Treatments included bifenazate (Acramite 50 WS at 1 lb/ac), abamectin (Agri-Mek SC at 4.29 fl oz/ac), entomopathogenic fungus Beauveria bassiana (BotaniGard ES at a lower label rate of 1 qrt/ac) + bifenazate (Acramite 50 WS at the lowest label rate of 0.75 lb/ac), rosemary and cotton seed oil (Eco-Mite at 1% concentration), fenpyroximate (Fujimite 5 EC at 2 pt/ac), fenpyroximate (Fujimite XLO at 2 pt/ac), Chromobacterium subtsugae strain PRAA4-1 (Grandevo at 2 lb/ac), Burkholderia sp. strain A396 (Venerate XC at 2 gal/ac), and cyflumetofen (Nealta SC at 13.7 fl oz/ac). A spray volume of 150 gal/acre was used with 0.25% non-ionic surfactant except for the treatment with B. bassiana, where an organo-silicon surfactant was used. Each treatment had a 15' long strawberry bed and treatments were replicated in randomized complete block design. Treatments were applied using a CO2 pressurized backpack sprayer twice at weekly intervals and eggs and mobile stages of twospotted spider mites and predatory mites were sampled 3 and 7 days after each application. On each sampling date, 10 mid-tier leaflets were collected from 10 random plants within each plot and mites were collected using a mite brushing machine and counted under microscope. Data were analyzed using analysis of variance and significant means were separated using Tukey's HSD test.
Pre-treatment counts were not available due to a technical issue, so comparisons were made for pest and predatory mite counts after each spray application and the post-treatment period as a whole. Compared to untreated control, treated plots had fewer spider mites throughout the observation period, but the pest suppression was not statistically significant (P > 0.05, Table 1). When the percent reduction in treatments relative to untreated control was compared, rosemary+cotton seed oil, fenpyroximate EC, and B. bassiana+bifenzate had relatively higher reduction in mobile stages while Burkholderia sp., rosemary+cotton seed oil, and cyflumetofen had a higher reduction in eggs after the first spray application (Fig. 1A). Reduction in mobile stages following the second spray was the highest in cyflumetofen followed by bifenzate, rosemary+cotton seed oil, fenpyroximate XLO, and EC (Fig. 1B). After the second spray, the highest reduction in eggs was seen in fenpyroximate EC followed by Burkholderia sp., cyflumetofen, rosemary+cotton seed oil, and B. bassiana+bifenzate. In general, rosemary+cotton seed oil treatment did a better job of reducing egg and mobile stages after both applications followed by Burkholderia sp., cyflumetofen, and fenpyroximate EC (Fig. 1C).
Table 1. Number of eggs or mobile stages (mean+SE) of twospotted spider mite 3 and 7 days after first and second spray treatment along with post-treatment average.
Fig. 1. Percent reduction in eggs and mobile stages of twospotted spider mites in different treatments compared to untreated control after first (A), second (B), and both spray applications (C).
There were no statistically significant differences in predatory mite populations among treatments except in mobile numbers on 7 days after the first spray (P = 0.0046, Table 2). Plots that were treated with Burkholderia sp. and cyflumetofen had a relatively higher number of predatory mites and bifenzate and abamectin had lower numbers, in general.
Table 2. Number of eggs or mobile stages (mean+SE) of predatory mites 3 and 7 days after first and second spray treatment along with post-treatment average.
Although treatment differences were not statistically significant, this study demonstrates the efficacy of various botanical, chemical, and microbial pesticides against twospotted spider mites and their safety to predatory mites. Results show the potential of non-chemical alternatives, which can be used in rotation with chemical pesticides for a sound IPM program.
General IPM recommendations:
- Obtain transplants from a clean source to avoid early spider mite infestations, which could lead to season long problems in production fields.
- Periodically scout the fields to evaluate infestation levels and make appropriate management decisions.
- Rotate chemicals among different modes of action groups and consider botanical and microbial control options to reduce the risk of resistance development.
- Understand the dietary preferences and environmental requirements of different species of predatory mites and release the right species appropriate for the situation.
- Avoid water stress for plants as spider mites thrive when plants are under stress.
- Excessive nitrogen fertilization encourages spider mite population build up, so optimize fertilizer input.
Acknowledgments: Thanks to Dave Peck, Manzanita Berry Farms, Santa Maria for his collaboration, pesticide industry partners for the financial support, and Sumanth and Suchitra Dara for their technical assistance with mite brushing.
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References
Blecker, S. 2015. Pesticide use trends in strawberries. Presentation at Santa Maria Strawberry Field Day. http://cesantabarbara.ucanr.edu/files/213517.pdf
Dara, S. K. 2014. Managing spider mites in California strawberries. UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13943
Dara, S. K. 2014. Predatory mites for managing spider mites on strawberries. UCCE eNewsletter Strawberries and Vegetables. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14065
Hoffland, E., M. Dicke, W. V. Tintelen, H. Dijkman, and M.L.V. Beusichem. 2000. Nitrogen availability and defense of tomato against two-spotted spider mite. J. Chemical Ecol. 26: 2697-2711.
- Author: Cheryl Reynolds
As summer continues to heat up, keep in mind that regulations remain in effect to reduce the volatile organic compounds (VOCs) that can be emitted into the atmosphere by pesticides and other harmful chemicals and contribute to the amount of ozone or smog in the environment.
Calculators from the Department of Pesticide Regulation (DPR) that determine the VOC emissions from fumigant and non-fumigant pesticides before application are available to help growers, pest control advisers, and pesticide applicators comply with the regulations. The UC Statewide Integrated Pest Management (IPM) Program provides a link to these calculators from each of the treatment tables in the UC Pest Management Guidelines. Click on the Air Quality – Calculate emissions button.
Take steps to reduce VOCs. Avoid emulsifiable concentrate (EC) formulations as they release the highest VOC emissions. Pesticide control advisers and growers can also reduce VOC emissions by employing IPM practices such as using resistant varieties, traps, exclusion, and biological control. When using pesticides, spot-treat and seek low-emission materials. Solid formulations, such as granules or powders, are best.
Check the fact sheet on the DPR web site for the most up-to-date-information on VOC restrictions and regulations.
- Author: Steve A. Fennimore
- Author: Richard F. Smith
- Author: Surendra K. Dara
- Author: John S. Rachuy
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Lettuce field at Betteravia Farms, Santa Maria
ABSTRACT
Few herbicides are available for use in lettuce and more effective weed control tools are needed. Previous studies have found Prowl H2O (pendimethalin) to be safe to transplanted lettuce and effective on weeds that commonly infest lettuce fields. The study objective was to compare the safety and efficacy of pendimethalin applied to lettuce before (PRE) and after (POST) transplanting in commercial plantings and field station evaluations on the California central coast. Pendimethalin applied PRE transplanting resulted in little lettuce injury and provided acceptable weed control. Lettuce yields were not reduced by pendimethalin. While the level of injury was low with the pendimethalin POST transplant application, the PRE transplant application caused even less injury than the POST. Pendimethalin at 2.1 pt/Acapplied PRE or POST transplant controlled 68% and 53%, of the weeds, respectively, compared to 12% for Kerb (pronamide). In the commercial evaluations there was no difference in the numbers of marketable lettuce heads or head weights between pendimethalin and the hand weeded control. Results here show that pendimethalin has potential for use in transplanted lettuce and controls weeds as well or better than pronamide.
OBJECTIVES
The objective of this work was to determine the safety of PRE and POST applications of pendimethalin to transplanted lettuce and efficacy on common weeds of lettuce.
Procedures
Pendimethalin PRE and POST Applications. One month old lettuce plants (3 to 5 true leaf stage) were transplanted into twin row 40-inch wide beds. The in-row plant spacing was 9 inches, between row spacing was 12 inches and plots were one bed wide by 25 feet long. Prowl H2O 3.8 lb/Gal. (pendimethalin) was applied at 2.1 and 4.2 pts/A and Kerb 3.3 SC (pronamide) was applied at 2.5 pts/A PRE one day before transplanting and POST, one day after transplanting. The pendimethalin 2.1 pts/A treatment was included as the normal 1X rate, the 4.2 pts./A rate was included as a 2x rate to verify safety to lettuce. Each trial had a no herbicide non-weeded control and a weed-free control. Weed densities were measured in 2.8 ft2 sample areas about 3 weeks after transplanting. Crop injury estimates were recorded on a scale of 0% (no injury) to 100% (dead). Lettuce yield (fresh weights) was determined by harvesting a 9 feet long sample area from one plant line in the middle of the plot. Experiments were repeated in 2013 and 2014, and were arranged in a randomized complete block design with four replications. Injury, weed density and yield data were subjected to ANOVA and means were separated by Fisher's protected LSD at α ≤ 0.05.
Commercial Field Evaluation. The on-farm evaluations were held with cooperating growers in Las Lomas and Santa Maria. Pendimethalin was applied PRE at 2.1 pts/A one day before transplanting. Lettuce yield in Las Lomas was sampled from an 18 ft long sample area on one bed (4 plant lines). Lettuce yield in Santa Maria was sampled from one plant line by 30 feet long. The on-farm evaluations included a hand weeded control. Experiments were arranged in a randomized complete block design with three replications. Data were subjected to ANOVA and means were separated by Fisher's protected LSD at α ≤ 0.05.
Results and Discussion
Pendimethalin PRE and POST Applications. The PREpendimethalinapplications at 2.1 and 4.2 pts/Awere safe for transplanted lettuce and resulted in minor crop injury of 12% or less (Table 1). POST transplant applications of pendimethalin resulted in 0 to 7% injury in 2013. POST applications of pendimethalinin 2014 resulted in 22% and 24% injury for the 2.1 and 4.2 pts/Atreatments, respectively. While the level of injury was very low, injury was more evident in the POST transplant pendimethalin applications than in the PRE transplant applications. Lettuce yields were not reduced by PRE or POST pendimethalin or pronamide applications relative to the nontreated control, indicating that transplanted lettuce plants have similar levels of tolerance to both herbicides (Table 1).
The primary weeds in these experiments (average between 2013 and 2014) were 68% annual sowthistle (Sonchus oleraceus L.), 12% shepherd's-purse, 10% burning nettle (Urtica urens L.) and 8% hairy nightshade (Solanum physalifolium). Under high weed densities in 2013, pendimethalin at 2.1 pts/Aprovided 69% and 53% weed control respectively in the PRE and POST transplant treatments (Table 1). By comparison pronamide provided 12% and 39% weed control respectively in the PRE and POST transplant treatments. Annual sowthistle was the main weed in 2013; a species poorly controlled by pronamide. Hairy nightshade was the main weed in 2014, a species well controlled by pronamide, and the reason why pronamide performed better in 2014 than 2013.
Table 1: Injury estimates, transplanted lettuce yield (fresh weights) and total weed control resulting from pendimethalin PRE and POST applications, in 2013 and 2014 on the field station evaluations. Note: yields were combined for 2013 and 2014.
a Means with the same letter within columns are not significantly different according to Fisher's Protected LSD at P < 0.05.
b Visible injury estimates were taken 15 and 25 days after treatment for the 2013 and 2014 experiments, respectively; estimates were taken on a scale of 0%-100%, with 0% = no injury and 100% = dead plants.
c Yield was evaluated 48 and 59 days after treatment for the 2013 and 2014 experiments, respectively.
d Weed control was measured 25 and 23 days after treatment for the 2013 and 2014 experiments, respectively. The main weeds in this experiment were 68% annual sowthistle, 12% shepherd's-purse, 10% burning nettle and 8% hairy nightshade.
Commercial Field Results. Evaluations of pendimethalin in commercial fields found similar results to the research station evaluations. At both locations, there was no significant difference in the numbers of marketable lettuce heads or yield between pendimethalin and the hand weeded control (Table 2). Differences in yield between locations were mainly due to differences in lettuce varieties and corresponding cropping practice such as plant densities.
Table 2. Transplanted lettuce yield, number of marketable heads and fresh weights, from the on-farm study of pendimethalin held in Las Lomas and Santa Maria in 2013 and 2014, respectively.
a There were no differences between the treatments according to Fisher's Protected LSD at P < 0.05.
We concluded thatpendimethalin (PRE and POST) at 2.1 pts/Awas safe for use on transplanted lettuce, and resulted in better weed control than pronamide. For transplanted leaf lettuce, pendimethalin is a viable product and registration of this product on lettuce should be pursued.
Grower standard on the left and pendimethalin (Prowl H2O)-treated plots on the right at Babe Farms, Santa Maria
Acknowledgments: Thanks to California Leafy Greens Research Board for funding this study and Craig Sudyka, Betteravia Farms and Jason Gamble, Babe Farms, Santa Maria for their collaboration in Santa Maria studies.
- Author: Surendra K. Dara
IPMinfo
Extending research information is an important part of Cooperative Extension. As communication technology is advancing every day, using modern channels of communication are important for successfully reaching out to growers, PCAs, and other key players of the agriculture industry. Electronic newsletters - Strawberries and Vegetables and Pest News, traditional newsletter – Central Coast Agriculture Highlights, Facebook posts, Twitter feeds - @calstrawberries and @calveggies, and Tumblr posts, and online repository of meeting handouts and presentations are some of the tools that play a critical role in making important information about my strawberry and vegetable extension program readily available to the agricultural industry. Popularity of smartphones has made all these sources handy, both literally and figuratively. Smartphone applications are becoming popular in agriculture to provide information, monitor various aspects, and for decision making. However, there are no such applications to help California strawberry and vegetable growers. In an effort to provide easy access to pest and disease information on various crops, IPMinfo was developed and is currently available for free download for iPhones on App Store. The first version was released in December, 2014 and an updated version was released in April, 2015.
IPMinfo is the first IPM information app from University of California and currently has information on strawberry pests and diseases. It provides one-touch access about the biology, symptoms of damage, and management options of pests and diseases to agricultural professionals.
Download IPMinfo from App Store for iPhones
To download the app on iPhones, go to the App Store and search for IPMinfo. Main features of the app are described below:
Overview screen allows access to different components of the app
Home: Takes the user to the crop issues – Pests and Diseases. Pests include aphids, cyclamen mite, greenhouse whitefly, lygus bug, spider mite, and western flower thrips. Diseases include angular leaf spot, anthracnose, botrytis fruit rot, charcoal rot, common leaf spot, fusarium wilt, leaf blotch and petiole blight, leather rot, mucor fruit rot, pytophthora crown rot, powdery mildew, red stele, rhizopus fruit rot, verticillium wilt, and viral decline. Each pest has information on its biology, damage symptoms, and management options and associated photos. Links provided on the management section will take the user to UC IPM website that has more detailed information especially about various control options. Tapping on the picture will enlarge and allows the user to zoom in. Disease section has information on symptoms and management options along with pictures.
After choosing the crop (which is just strawberries for now) either pest or disease topics can be selected.
List of the arthropod pests and access screen for biology, damage, and management.
Example of lygus bug biology, damage, and management sections.
Double tap the image to expand and pinch to zoom in.
List of bacterial, fungal, and viral diseases of strawberries
Disease symptoms and management options can be accessed from these screens.
Discover: Brief introduction to the app and what it does.
About Us: General information about the app, photo credits, and an option to send me an email.
Discover the app and send feedback from these screens.
Pest News: Provides a list of articles on my eNewsletter, Pest News. Tapping on the title of the article will take you to the newsletter through the app.
Berries-Veggies: Provides a list of articles on my eNewsletter, Strawberries and Vegetables. Tapping on the title of the article will take you to the newsletter through the app.
Articles on eNewsletters, Pest News and Strawberries and Vegetables can be accessed from these screens.
Having an app for like IPMinfo facilitates an easy access, especially when out in the field or not at the computer, to a quick summary of various pests and diseases, pictures to help identify the issue, and links to provide additional information.
- Author: Tunyalee Martin
- Author: Chris Laning
Identifying nontarget crop and ornamental plant damage from herbicides has become much easier with the launch of a new online photo repository by the Statewide IPM Program, University of California Division of Agriculture and Natural Resources.
Herbicides applied to manage weeds may move from the site where it was applied in the air or by attaching to soil particles and traveling as herbicide-contaminated soil. When an herbicide contacts a nontarget plant, a plant it was not intended to contact, it can cause slight to serious injury. Herbicide injury also occurs when the sprayer is not properly cleaned after a previous herbicide application. Herbicide residue can be found in the spray tank, spray lines, pumps, filters and nozzles so a sprayer must be thoroughly cleaned after an application. Dry herbicide particles can be redissolved months later and cause herbicide damage to plants. Economic damage includes reduced yield, poor fruit quality, distorted ornamental or nursery plants, and occasionally plant death.
Accurately diagnosing plants that may have herbicide injuries is difficult. In many cases, herbicide symptoms look very similar to symptoms caused by diseases, nutrient deficiencies, environmental stress and soil compaction. Plant disease symptoms such as mottled foliage, brown spots or stem death and plant pests such as insects or nematodes cause foliage to yellow and reduce plant growth similar to herbicide injury.
Dr. Kassim Al-Khatib, weed science professor at UC Davis and director of the UC Statewide Integrated Pest Management Program (UC IPM), has gathered nearly a thousand photos of herbicide-damaged plants, drawn from his own and others' research. The images are cataloged to show damage that can occur from 81 herbicides in more than 14 specific herbicide modes of action, applied in the field to demonstrate the symptoms or when known herbicide spray has drifted onto the plant.
Each image is characterized with the name of the plant, mode of action of the herbicide, and notes the specific symptoms of damage. Together these photos provide a comprehensive archive of damage to over 120 different crops and ornamental plants by known herbicides, which users can easily compare with what they see in the field.
Also included in the repository is information about the modes of action of various herbicides and an index of example herbicide trade names and active ingredients. Users can learn how unintended injury from herbicide occurs from misapplication and carryover from previous crops in addition to drift and herbicide-contaminated tanks.
The repository can be found at http://herbicidesymptoms.ipm.ucanr.edu. Increased knowledge about what causes herbicide damage and how it occurs can lead to fewer cases of herbicide injury occurring through drift or herbicide-contaminated tanks. Using the repository can increase the skill to correctly identify plant damage. Correctly identifying damage as herbicide injury and not from a plant pest or nutrient deficiency can prevent unnecessary applications of pesticides or fertilizers. Fewer applications can lessen the risk of harm of pesticides and fertilizers to people and the environment.