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Weed management with pendimethalin in Central Coast lettuce


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.

Posted on Thursday, June 18, 2015 at 1:22 PM

New invasive pest, the ficus eye-spot midge, Horidiplosis ficifolii in California

Deformed and yellowing foliage of Indian laurel fig infested with the ficus eye-spot midge.  Photo: Tracy Ellis.

San Diego County entomologist, Tracy Ellis recently reported the occurrence of a small gall midge in Rancho Santa Fe and La Jolla.  Established populations of the ficus eye-spot midge, Horidiplosis ficifolii Harris & de Goffau 2003 (Diptera: Cecidomyiidae) were found in Indian laurel fig (Ficus microcarpa var. nitida) in late 2014.  Early last year, another exotic pest, weeping fig thrips (Gynaikothrips uzeli) was found infesting weeping fig (F. benjamina).

Origin and Distribution:  Eye-spot midge is native to South East Asia.  It was first described from the infestations in weeping fig imported from Taiwan to the Netherlands which later moved to UK.  Galls collected in UK and larvae and adults reared in Denmark and the Netherlands were used to describe the pest.  Eye-spot midge was later reported in Italy in 2007, USA (Florida) in 2008, and the Czech Republic in 2010. 

Host range:  It appears to be a primary pest of ornamental figs.  In California, Florida and the Czech Republic, eye-spot midge was found on the Indian laurel fig, in Denmark, UK, and the Netherlands on the weeping fig, and in Italy on a host referred to as ornamental fig.

Damage:  Larvae form galls on young leaves.  Galls are irregularly shaped and about 4 mm in diameter.  When larvae exit the galls for pupation, galls collapse and become dark brown, sunken spots that could be mistaken for leaf spots caused by bacterial or fungal diseases.  Circular exit holes of 1-2 mm diameter can be seen on older galls.  Heavy infestations could lead to leaf fall.


Mature galls turning into dark, sunken spots.  Round holes formed by larvae exiting the galls.  Photo: Tracy Ellis.

Biology:  Information on eggs is lacking, but they are probably deposited on foliage.  Young larvae are translucent.  They make galls and develop individually inside each gall.  Mature larvae are bright orange and exit the galls to pupae in the soil or other substrates.  Adults are small midges with brownish orange bodies and are weak fliers.  Life cycle is completed in about one month at 20oC or 68oF.

Ficus eye-spot midge life stages.  Photo: Tracy Ellis.

Management:  There are no specific management options reported in any literature except for the removal and destruction of the infested foliage.  

What to do: If you suspect ficus eye-spot midge infestations, please inform your local Ag Commissioner or University of California Cooperative Extension office.

References

Beránek J. and I. Šafránková I. 2010. First Record of Horidiplosis ficifolii Harris 2003 (Diptera: Cecidomyiidae) in the Czech Republic. Plant Protect. Sci. 46: 189–191.

Caldwell. D.  2012.  Ficus trees under attack! https://palmbeachcountyextension.files.wordpress.com/2012/01/ficus-trees-under-attack.pdf

Harris K.M. and L.J.W. De Goffau.  2003. Horidiplosis ficifolii, a new species of gall midge (Diptera: Cecidomyiidae) damaging ornamental fig plants, Ficus benjamina L. Tijdschr. Ent. 146: 301–306.

Steck G.J. and S. Krueger.  2008. An ornamental fig pest, Horidiplosis ficifolii Harris (Diptera: Cecidomyiidae), genus and species new to Florida and North America.  http://www.freshfromflorida.com/Divisions-Offices/Plant-Industry/Plant-Industry-Publications/Pest-Alerts/Pest-Alerts-An-Ornamental-Fig-Pest-Horidiplosis-Ficifolii-Harris-Diptera-Cecidomyiidae

Suma P., A. Russo A. and S. Longo.  2007. Horidiplosis ficifolii (Diptera Cecidomyiidae) infestante su Ficus ornamentali in Sicilia. In: Proceeding XXI Congresso nazionale italiano di Entomologia, Catania 10–15 Giugno: 230.

Taxonomic description on Fauna Europaea http://www.faunaeur.org/full_results.php?id=303211

van der Gaag, D. J., E. Dijkstra, W. Lammers, A. Meijer, and E. J. Scholte.  2006.  Pest risk analysis: Horidiplosis ficifolii Harris. https://www.nvwa.nl/txmpub/files/?p_file_id=2000933

Posted on Friday, June 5, 2015 at 11:50 AM

IPM information app from University of California about strawberry pests and diseases


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.

Posted on Friday, May 8, 2015 at 1:09 PM

New videos from UC IPM help stone fruit growers and PCAs tackle pest problems

Spider mites, fruit moth and twig borer larvae, aphids, and bark cankers are just a few pests that can wreak havoc on stone fruit trees.   With spring well underway and trees in full bloom and beginning to develop fruit, it's time to monitor and take action before these pests get out of hand. 

UC IPM teamed up with UC farm advisors to develop a series of how-to videos that can help growers and pest control advisers monitor for pests and damage and determine if and when treatment is needed.

In one video, Sacramento Area IPM Advisor Emily Symmes gives a brief overview of how to monitor for webspinning spider mites.  Spider mites build up in stone fruit trees as the weather warms up.  Late spring through summer is the ideal time to monitor for mites and their damage, which includes leaf stippling and webbing.  If mites build up too much, leaves can drop, fruit may not fully develop, and branches and fruit can be exposed to sunburn. 

Shoot strikes, or dead drooping leaf tips, are often seen on young peach and nectarine trees.  In a second video, UC Sutter and Yuba County Farm Advisor Janine Hasey explains how to monitor for shoot strikes and how to distinguish the culprits, oriental fruit moth and peach twig borer.  Although Oriental fruit moth and peach twig borer can bore into both foliage and fruit, they cause the most devastating damage by feeding on fruit.  Early season monitoring and treatment can prevent future fruit loss.

In plum and prune orchards, leaf curl aphids and mealy plum aphids cause leaves to curl and become distorted.  Aphids produce honeydew, which can lead to the development of sooty mold, causing fruit to crack and blacken.  Aphids are often present when leaves start to grow.  In his video, Rick Buchner, UC farm advisor for Tehama County, discusses how to monitor for aphids and explains how to decide when treatment is warranted. 

In a final video, UC Sacramento County Farm Advisor Chuck Ingels teaches how to distinguish Phytophthora root and crown rot from bacterial canker.  The two diseases are often confused because they both cause bark cankers.   Phytophthora root and crown rot is confined to the lower trunk, but when a bacterial canker infection occurs in the tree trunk, the diseases can often be confused.  Bacterial canker can be confirmed by cutting away the outer bark and looking for characteristic red flecks on the inner bark.  Correct identification of these diseases will help in choosing a management strategy.

You can find all of these how-to videos on the UC IPM video library page.  For specific information about managing pests in stone fruits or other crops, see the Pest Management Guidelines.

Posted on Thursday, April 16, 2015 at 10:47 AM

New UC IPM photo repository shows plant damage from herbicides

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.

 

Posted on Thursday, April 9, 2015 at 9:48 AM
  • Author: Tunyalee Martin
  • Author: Chris Laning

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