Update on Bacterial Leaf Streak of Corn in Nebraska

Feb. 23, 2017

http://cropwatch.unl.edu/2017/update-bacterial-leaf-streak-corn-nebraska

Terra Hartman – Graduate Research Assistant
Tamra Jackson-Ziems, Extension Plant Pathologist

Bacterial leaf streak disease of corn is caused by the bacterium Xanthomonas vasicola (syn. X. campestris pv. zeae). It was previously only reported on corn in South Africa, and had not been reported in the United States until August 2016.

Nebraska map showing counties with bacterial leaf streak.
Figure 1. Distribution of bacterial leaf streak in Nebraska in 2016. The pink color indicates that bacterial leaf streak was confirmed in at least one sample received from that county. Unshaded counties indicate a lack of samples submitted or that those submitted tested negative.

This bacterium is most noted for causing gumming disease, a leaf blight and vascular wilt that affects sugarcane. The vascular wilt phase has not been observed in corn.

Bacterial leaf streak has been confirmed in Nebraska, Colorado, Kansas, Iowa, Minnesota, South Dakota, Illinois, and Texas. A 2016 survey funded by the Nebraska Corn Board confirmed that bacterial leaf streak was present in at least 51 Nebraska counties (Figure 1) across much of the state. The pathogen was not detected in samples from some extreme eastern and western counties. These results don’t necessarily indicate its absence, but rather may be due to a lack of representative samples from those areas, especially considering the disease has been confirmed in several adjacent counties in neighboring states.
Symptoms

Sampling of bacterial leaf streak lesions of corn

Figures 2-4. Bacterial leaf streak lesions may vary in color and length, but will be between veins and often have wavy margins.

Symptoms include yellow, tan or dark to light brown striped lesions with wavy margins that can appear on the leaf blade (Figures 2 and 3) or be concentrated around the midrib (Figure 4).
bacterial leaf streak lesions
Figure 5. Lesions may appear bright yellow when backlit.

These lesions can appear yellow when backlit (Figure 5). Symptoms have been observed on the lower leaves as early as the beginning of June in Nebraska on V7 corn, and tend to move up the plant as the infection progresses. While this seems to be the normal pattern for disease development, there have been cases where symptoms first appeared in the mid-canopy or upper leaves during mid-season.

Bacterial leaf streak and gray leaf spot are often mistaken for each other due to their similar appearance and behavior. There are two key differences to look for when trying to distinguish between these diseases:

First, consider the time of year when the symptoms develop. If the symptoms first developed in June, it is likely bacterial leaf streak, as cooler weather conditions in Nebraska are not often favorable for gray leaf spot development.

Second, examine the margins of the leaf lesions. Bacterial leaf streak typically has a wavy margin, whereas gray leaf spot lesions usually have smooth, linear margins (Figures 6 and 7).

Gray leaf spot and bacterial leaf stripe

Figures 6 and 7. Gray leaf spot lesions (left) versus bacterial leaf streak lesions (right) on corn. Note the wavy margins of the bacterial leaf streak lesions versus the smooth, linear margins of the gray leaf spot lesions.

While these considerations can be useful, neither can be used exclusively to diagnose these diseases every time, especially when both diseases are present on the same leaf.

Be sure to observe many lesions on several plants and always submit a sample for diagnosis if you’re unsure of a diagnosis or if you suspect the bacterial leaf streak has developed in a new area.

Epidemiology

Xanthomonas vasicola is capable of overwintering in infested residue, where it can survive until environmental conditions become favorable for it to infect the next year’s crop. This bacterium does not require wounds to establish an infection, and it is believed to enter the plant through natural openings, such as the stomata.

Center pivot irrigation and wind-driven rain may increase the severity of infection by creating conditions that allow the pathogen to enter the plant’s natural openings, such as stomata. Bacterial leaf streak has been confirmed in dent (field) corn, popcorn, seed corn, and sweet corn.
Favorable Conditions

This pathogen is favored by warm, humid conditions, and is thought to be spread by wind-driven rain.
Management

When making management decisions, it is important to verify the diagnosis. Bacterial leaf streak and the common fungal disease, gray leaf spot, can appear very similar in some hybrids and the fungicides used to treat gray leaf spot are not expected to be effective against bacterial leaf streak.

Resistance to the bacterial leaf streak pathogen has not been confirmed in corn, so resistant hybrids are not available. Crop rotation to a non-host crop may help reduce disease severity in future corn crops, however disease development has been observed after one-year rotations to soybeans, wheat, and after fallow. Rotation alone won’t prevent bacterial leaf streak.

Tillage may reduce disease severity by promoting degradation of the infested crop debris source, but it will not eliminate the disease. Cleaning equipment when moving from an infested field to a disease-free field may slow the spread of the disease. These are standard practices for mitigation of bacterial diseases, but none of them will eliminate the pathogen and some may be impractical in some production systems.
For More Information
Nebraska Extension Plant Pathologist Tamra Jackson-Ziems talks with Market Journal host Jeff Wilkerson about bacterial leaf stripe in corn.

If you have questions about bacterial leaf spot, please contact Nebraska Extension Plant Pathologist Tamra Jackson-Ziems at 402-472-2559 or tjackson3@unl.edu.

Additional resources include:

Bacterial Leaf Streak of Corn Confirmed in Nebraska, Other Corn Belt States
Bacterial Leaf Streak in the CropWatch Plant Disease Management section
Corn Disease Management: Bacterial Leaf Streak published by the Crop Protection Network in December 2016.

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Spider mite control in corn aided by moisture

From IPM inthe South by Rosemary Hallberg

by Kay Ledbetter, Texas A&M AgriLife

The Texas A&M AgriLife Extension Service has a list of do’s and don’ts when it comes to spider mite treatment on corn, according to Dr. Ed Bynum, AgriLife Extension entomologist in Amarillo.

Spider mite damage can reduce corn silage yields about 17 percent and grain yield production by 23 percent or more when not controlled, Bynum said, speaking recently at the High Plains Irrigation Conference in Amarillo.

He said spider mites reduce yields by desiccating leaf tissue, which lowers chlorophyll content and reduces transpiration and photosynthesis. Mite feeding also reduces plant water-use efficiency.

Spider mites are a pest in arid regions that reproduce most rapidly on moderately drought-stressed plants, he said. One female produces 45-100 eggs and they live in colonies. It takes about 10 days for them to go from egg to adult.

“So you can have as many as 11 generations in a summer growing season in the High Plains,” Bynum said.

“The key is to know which species you have and what causes them to increase,” he said. “The Banks grass mite and two-spotted spider mite both feed the same. The Banks grass mite is more common early in the season and stays on the lower portion of the plant, moving up as the population develops. The two-spotted mite is spread out on the plant throughout the growing season.”

Bynum said the list of do’s and don’ts includes:

– Don’t let the corn stress from moisture or heat, especially moisture because it adds to the heat stress.

– Don’t over fertilize.

– Scout fields at least once a week to know if mite and predator populations are increasing, decreasing or staying static.

– Spray before mite populations get out of control.

– Improve the application coverage by getting it down into the canopy.

– Spray early in the morning to keep it from evaporating.

Damage assessment is based on a scale of 1-10, Bynum said.

“We used to advise waiting until a level 5, but with the miticides that we have now, we can’t get the quick control,” he said. “We are advising the damage level of 3, between 21-30 percent plant damage where none of the lower leaves are killed or have excess injury, is the mark for making a miticide application now.”

Bynum said grain corn is only safe after the dent stage is reached, so any infestation prior to that may need to be treated if infestations reach the outlined damage level. Heavily infested plants are prone to stock rot.

“Sometimes people don’t recognize how much loss can occur,” he said. “Some producers may want to control mites at the whorl stage, however at that point you don’t know what the predator populations will do to keep the mite populations under control.

“Most of the control treatments, therefore are made during tassel and grain-filling growth stages. At tassel, the plant chemistry changes and the mites can explode in population.”

In general, Bynum said, spider mites are affected by moisture stress conditions. When corn is kept wet both before and after tassel, mite populations are generally lower. The higher the total season water, the lower density of spider mites. When the crop is kept drier, it supports mites earlier in the season and longer.

Maturity levels of the corn, however, can make a difference. In one study comparing combinations of early maturity, early planted, latematurity, late-planted corn on six levels of water – fully irrigated down to dryland – demonstrated different infestation levels of mites.

Early maturity and early planted with high levels of irrigation had lower mite levels across all water gradients, Bynum said. Early maturity, lateplanted under higher water levels didn’t have as many mites, but mite populations increased as the soil moisture was reduced.

The late-maturity, early planted corn had lower mite infestations at the higher water levels, but increased to high populations during the moderate water levels, and then dropped off to lower populations under drought-stressed conditions.

The late-maturity, late-planted corn generally had low levels of mites at all the different irrigation levels, but Bynum said that might have been because the plants at the drier moisture levels were under greater moisture stress conditions.

“When we allow spider mites to cause excessive damage, we’re really robbing from the water applied to the crop,” he said. “Producers need to be managing those spider mites out there.”

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SARE’s Revised How to Conduct Research on Your Farm or Ranch is now available

Like all farmers, Harry Cope is an innovator who struggles to reduce costs while raising cattle and sheep on his Missouri farm. Cope wondered if forage production could be increased by planting a cover crop into standing corn for fall grazing. But establishing a cover crop is challenging when little sunlight reaches the soil surface. So Cope decided to conduct research to test whether skipping some rows when planting corn would allow more light to reach the soil and establish the cover crop more effectively.

On-farm research revealed that the extra space and light made no difference in the amount of forage produced. Although research is challenging and time consuming, it helped Cope refine his ideas about cover crop management. Now, SARE’s newly revised How to Conduct Research on Your Farm or Ranch is available to help more experimenting farmers like Cope succeed.

How to Conduct Research on Your Farm or Ranch
provides detailed instructions for crop and livestock producers, as well as educators, on how to conduct research at the farm level using practical strategies and peer-reviewed research findings. How to Conduct Research on Your Farm or Ranch also includes a comprehensive list of in-depth resources and real-life examples—from a Missouri crop and livestock farmer testing the effect of additional cover cropping on forage available to his animals to a West Virginia organic producer experimenting with an integrated trap crop and pheromone trap system for ecological management of stink bugs.

Download or order your free print copy of How to Conduct Research on Your Farm or Ranch at sare.org/research or by calling (301) 779-1007. How to Conduct Research on Your Farm or Ranch is also available to educators in quantity for use in educational workshops, classes or tours.

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Iowa State seeks Resistance Management Program Manager

IPRMP program manager 

 

https://www.iastatejobs.com/postings/24653

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University of Florida seeks assistant professor of plant pathology

Location: Tropical Research and Education Center (TREC), University of Florida, Institute of Food and Agricultural Sciences (IFAS), Homestead, Florida

Deadline: For full consideration, candidates should apply and submit additional materials by April 17, 2017. The position will remain open until a viable applicant pool is determined.

Duties and Responsibilities

This is a 12-month tenure-track position with 60% extension (Florida Cooperative Extension Service) and 40% research responsibilities. The incumbent will accrue tenure in the Department of Plant Pathology (Florida Agricultural Experiment Station), Institute of Food and Agricultural Sciences (IFAS), University of Florida and will be located at the Tropical Research and Education Center (TREC) in Homestead, FL.

The appointee is expected to provide leadership for the Plant Diagnostic Clinic by:

  • Analyzing plant samples submitted to the clinic using microbiological, histochemical, biochemical and/or microscopic techniques, to determine organisms or conditions associated with plant diseases and disorders.
  • Interacting with clientele and research and extension faculty to gather information necessary to accurately diagnose plant diseases and disorders and provide research-based management recommendations.
  • Developing new diagnostic methods for plant diseases and disorders
  • Providing in-service training for extension faculty and clientele.
  • Participating in the Southern Plant Diagnostic Network through its regional center at UF.
  • Supervising a laboratory technician.

The research portion of this position focuses primarily on the diagnosis and management of diseases of ornamental and landscape plants. The successful candidate is expected to seek competitive funding to support research and extension programs.

Because of the IFAS land-grant mission, all faculty are expected to be supportive of and engaged in all three mission areas—Research, Teaching and Extension—regardless of the assignment split specified in the position description.

Qualifications

Required:

This position requires a Ph.D. (foreign equivalent acceptable) in Plant Pathology, Plant Medicine, or a closely-related field and a strong interest or experience in clinical diagnosis of plant diseases. Candidates should have good organizational and managerial abilities and demonstrated verbal and written communication skills, interpersonal relations, and procurement of extramural funding. Candidates must support IFAS core values of excellence, diversity, global involvement, and accountability.

Preferred:

Postdoctoral experience is preferred.

Background Information

The Tropical Research and Education Center (TREC; http://trec.ifas.ufl.edu/) of the Institute of Food and Agricultural Sciences (http://ifas.ufl.edu), University of Florida (www.ufl.edu) is located in Homestead, Florida about 30 miles south of Miami. TREC was established in 1929 by an act of the state legislature in what is now Miami-Dade County. Currently, TREC consists of offices, laboratories, greenhouses, vegetable fields and fruit orchards on 160 acres. Research, teaching, and extension programs focus on tropical and temperate vegetable crops, tropical and subtropical fruit crops, and ornamental crops of southern Florida. The agricultural industry served by the center has an annual farm gate value in excess of $1 billion. Multiplier effects make agriculture’s impact on the local economy worth over $2 billion annually. The area’s oolitic limestone soil is unique to extreme southern Florida, and due to the region’s humid subtropical climate, TREC is the only state university research center in the continental United States focused on a large number of tropical and subtropical crops. The center also addresses crop-related water and environmental issues that result from its proximity to Everglades National Park, Biscayne National Marine Park, Florida Bay and major well fields that provide drinking water to the several million people in neighboring urban areas.

The University of Florida (http://www.ufl.edu) is a Land-Grant, Sea-Grant, and Space-Grant institution, encompassing virtually all academic and professional disciplines, with an enrollment of more than 53,000 students. UF is a member of The Association of American Universities. The Institute of Food and Agricultural Sciences (http://ifas.ufl.edu) includes the College of Agricultural and Life Sciences (http://cals.ufl.edu), the Florida Agricultural Experiment Station (http://research.ifas.ufl.edu), the Florida Cooperative Extension Service (http://extension.ifas.ufl.edu), the College of Veterinary Medicine (http://www.vetmed.ufl.edu), the Florida Sea Grant program (http://www.flseagrant.org/ ), and encompasses 16 on-campus academic departments and schools, 12 Research and Educational Centers (REC) located throughout the state, 6 Research sites/demonstration units administered by RECs or academic departments, and Florida Cooperative Extension Service offices in all 67 counties (counties operate and maintain). The School of Natural Resources and Environment is an interdisciplinary unit housed in IFAS and managed by several colleges on campus. IFAS employs over 2500 people, which includes approximately 900 faculty and 1200 support personnel located in Gainesville and throughout the state. IFAS, one of the nation’s largest agricultural and natural resources research and education organizations, is administered by a Senior Vice President and four deans: the Dean of the College of Agricultural and Life Sciences, the Dean for Extension and Director of the Florida Cooperative Extension Service, the Dean for Research and Director of the Florida Agricultural Experiment Station, and the Dean for the College of Veterinary Medicine. UF/IFAS also engages in cooperative work with Florida A&M University in Tallahassee.

Employment Conditions

This position is available May 1, 2017 and will be filled as soon thereafter as an acceptable applicant is available. Compensation is commensurate with the education, experience, and qualifications of the selected applicant.

Nominations

Nominations are welcome. Nominations need to include the complete name and address of the nominee. This information should be sent to:

Please refer to Requisition # 501403

Dr. Bruce Schaffer
Chair, Search and Screen Committee
University of Florida
Tropical Research and Education Center
18905 SW 280th Street
Homestead, FL 33031
Telephone:  786-217-9265
Facsimile:  305-246-7003
Electronic Mail:  bas56@ufl.edu

Application Information

Individuals wishing to apply should go online to http://explore.jobs.ufl.edu/cw/en-us/job/501403 and submit:

  • Application
  • Cover letter that states applicant’s interest in the position and qualifications relative to the credentials listed above
  • Curriculum vitae
  • Contact information (including email addresses) for 4 individuals willing to write letters of recommendation
  • University transcripts

The final candidate will be required to provide official transcript to the hiring department upon hire. A transcript will not be considered “official” if a designation of “Issued to Student” is visible.  Degrees earned from an education institution outside of the United States are required to be evaluated by a professional credentialing service provider approved by National Association of Credential Evaluation Services (NACES), which can be found at http://www.naces.org/ .

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Protect trees when applying herbicides to weeds

From IPM in the South by Rosemary Hallberg

by Merritt Melancon, University of Georgia

It can take years for a tree to reach full maturity, but it only takes one or two seasons of damage to irreparably harm the biggest and most expensive piece of a well-designed landscape.

Drought, insects and blight can all cause damage to mature trees. But more often than not, when a mature tree takes a turn for the worse, the culprit may be human error.

“Extension agents get hundreds of these calls every summer,” said Paul Pugliese, University of Georgia Cooperative Extension coordinator for Bartow County. “People tell us they have an otherwise healthy tree, but this year it started producing damaged-looking leaves.”

In cases like this, symptoms may have been caused by accidental herbicide damage. Gardeners may be familiar with the rippling, curling and deformed leaves that accidental herbicide exposure can cause on vegetable plants and flowers. While it takes more herbicide to damage a tree, they’re not immune to that herbicide damage, Pugliese said.

Trees are usually exposed either through spray drift from a nearby herbicide application or by absorbing herbicides applied to lawns to prevent dandelions and other broadleaf weeds. When controlling lawn weeds, homeowners and landscapers should not apply herbicides near the root zones of trees and shrubs.

The damage is done

The amount of damage seen in the tree depends on the amount of herbicide absorbed by the tree and the area exposed.

Popular herbicides containing 2,4-D and other broadleaf weed killers are notorious for causing leaf curling, but other consumer and commercial herbicides can also cause deformities.

In many cases, the damage caused by the herbicide will be permanent. Deformed leaves one year means leaves will emerge deformed for the remainder of the tree’s life. Some trees will ultimately decline or die over the course of several years.

“Springtime is when you’re going to see these dramatic effects, when the leaves are pushing out and the herbicide is being drawn up into the tree,” Pugliese said.

Pugliese has seen deformed leaves with twisting and curling symptoms that look like pigs’ tails, leaves that appear scorched and leaves that look like they are drought-damaged, but feel like normal leaves. The severity of the deformity determines whether the tree will be able to continue to capture enough sunlight and produce enough energy to sustain itself.

How to know

There are lots of tree disorders that can cause similar symptoms, and not all damage is due to herbicides, he said.

It’s time to suspect herbicide damage if you’ve ruled out other factors, like water stress, viruses and insect damage. If the damage is limited to one species of shrub or plant in the landscape, insects or disease could have caused the damage.

“The unique thing about herbicide damage is that it’s going to be more widespread through the landscape in terms of the types of plants affected,” Pugliese said. “Insects and disease are going to be very host-specific, causing injury to one group of related plants. If you see multiple species of plants with injury, then that’s a good indication that you’re dealing with herbicide damage.”

Also, if damage appears on just one part of a tree, leaves on only that part of the tree may have been hit by some herbicide overspray.

The UGA Extension Agricultural and Environmental Services Laboratories offer plant tissue testing that can determine whether a tree or shrub has been exposed to an herbicide, but it is expensive – about $100 per sample.

Protection

The best course of action is to take extreme caution to avoid the root zone of trees and ornamental plants when applying lawn herbicides, Pugliese said. Homeowners and landscapers should avoid applying broadleaf herbicides on windy days, avoid applying them before rainy periods and avoid applying them above the root zones of trees.

Maintaining a mulch island on top of the tree’s roots not only conserves water and cools the roots, it can also protect against overspray. The mulch island should be expanded as the tree grows to cover an area larger than the width of the tree branches to avoid having to spray lawn herbicides too close to the tree’s roots. The rootball of a mature tree can extend up to two times as wide as the tree’s canopy.

For more information about safely applying herbicides to urban lawns, read the UGA Extension publication “Weed Control in Home Lawns” at extension.uga.edu/publications/detail.cfm?number=B978 or visit extension.uga.edu/publications.

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NEW: PhD Fellowships available in tick pathogen discovery

The National Institute for Microbial Forensics and Food and Agricultural Biosecurity (NIMFFAB) and the Center for Veterinary Health Sciences (CVHS) at Oklahoma State University are pleased to announce the availability of two graduate fellowships for highly qualified, motivated graduate students to pursue the PhD degree while completing mentored research in bioinformatics and pathogen discovery. Available projects involve microbiome and transcriptome analysis of ticks using next generation sequencing and novel platform queries to characterize new and emerging tick-borne pathogens of veterinary and public health importance. English fluency and basic programming skills are required; additional training in bioinformatics is recommended.

For more information, contact vbsc@okstate.edu or visit the Graduate College Application page to begin an application. Oklahoma State University is an equal opportunity employer committed to diversity.

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Missed the Palmer amaranth webinar? Recording is in YouTube

From IPM inthe South by Rosemary Hallberg

On Fe.15, Muthu Bagavathiannan, specialist in weed ecology and agronomy, presented a new tool for consultants, extension specialists and agents, and growers to assist with management decisions regarding Palmer amaranth, named PAM. Based in Microsoft Excel, the tool allows the user to input their rotation schedule, chosen varieties and other management practices. From those entries, the tool calculates the amount of weed seed present over a 10-year period, as well as the economic gains or losses during that period. In addition, it calculates the risk of the combination of practices and allows the user to compare up to 6 different management scenarios. The tool calculates risk based on the amount of weed seed present, which has been concluded to be the main reason for pigweed-related crop failures. 

You can get to the tool from this link.

If you would like to see Dr. Bagavathiannan’s presentation, follow this link to the YouTube recording. During the 60-minute video, he demonstrates how to use the tool and how to interpret the results.

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Lake Ontario Fruit Team seeksr a Production Economics Specialist

The Lake Ontario Fruit Team has an opening for a Production Economics Specialist. 

The link to the Cornell Careers posting is: http://tiny.cc/Economics_WDR_00010019

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Registration opens North American Invasive Species Forum set for may 9-11 in Savannah

Registration is open! Registration is $200 and includes three lunches and two dinners. Early Registration and Hotel Block is available until March 31. Optional Field Trips are available on Thursday Afternoon, May 11 – Saturday, May 13. Space is limited for some trips.

About the Forum

North American Invasive Species Forum – Building Cooperation Across Borders

http://www.invasivespecies2017.org

The North American Invasive Species Forum is a biennial conference encompassing the interests of professionals and organizations involved in invasive species management, research, and regulation in North America.

The Forum expands on the previous successes of the biennial Weeds Across Borders conferences, bringing together the international invasive species community. This Forum will include the latest information on policy and cross-border coordination of aquatic and terrestrial invasive species management – including discussions on innovative and effective approaches for collaboration with indigenous and tribal groups, local communities, government agencies, industry, not-for-profit organizations, and other stakeholders – with the objective of outlining a continental Strategic Framework for aquatic and terrestrial invasive species across North America.

In addition to the three-day event, with opportunities for post-forum field trips along the Georgia coast and a pre-forum workshop on invasive speecies mapping and data. The North American Invasive Species Network is hosting this Forum with the support of, and guidance from, an international steering committee representing the U.S., Canada, and Mexico. We hope that you will plan to enjoy the beautiful Coastal Georgia Botanical Gardens setting.

Meeting Location

Coastal Georgia Botanical Gardens

Way back when the property was a USDA plant introduction station, locals first affectionately dubbed it “the Bamboo Farm.” Today, as a facility within the University of Georgia Extension, it is now known as the Coastal Georgia Botanical Gardens.

Located 10 miles southwest of historic downtown Savannah, Coastal Georgia Botanical Gardens is also 19 miles inland from the Atlantic Ocean. It is in USDA Plant Hardiness Zone 8b, with an annual average minimum temperature of 15 to 20 degrees Fahrenheit. On average, there are about 140 summer days with temperatures above 86 degrees.

To learn more about the Coastal Georgia Botanical Gardens, please visit their website

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