Should our Garden Club Sell Impatiens? What is the risk for Impatiens Downy Mildew in Illinois?

These are good questions. This is because many people don't understand downy mildew of impatiens (Plasmopara obducens) .  When someone buys a plant and it gets sick, they often want to blame the person/business from where it was purchased.  However, in reality, it may not be the fault of that person/business.

I think you are on the right track if you have a "reputable supplier".  This means you are confident that the pathogen that causes downy mildew on impatiens is not going to be on the plants that you are selling.  When this disease first became a problem in the U.S., it was found  in a few nurseries and not in the landscape. Since 2011, it has become a problem in landscapes!  In Illinois, we are receiving reports that this disease is a problem in the Chicago area.  Some may want to know how they can be sure that an impatiens supplier is reliable.

 Plant or finish growers of impatiens may be more at risk for downy mildew infection if:

• Impatiens production is at the same time of impatiens growing in the landscape. -This is not likely in Illinois because plant production occurs during March or April.
• Impatiens plugs or liners are from an area where infected impatiens are currently growing or impatiens downy mildew has been reported in the landscape. - This could be likely if plugs are grown in Southern States and shipped here for finishing.
• Impatiens are growing in an area where impatiens downy mildew was confirmed in the landscape in 2011 or 2012. - This could be a problem for the finish grower or end user is they planted in a landscape bed where downy mildew existed previously.

All cultivars of impatiens walleriana are susceptible to downy mildew; however New Guinea impatiens have a high resistance to this disease.

For more information:   http://www.ballhort.com/Growers/_default.aspx 
                                    http://hyg.ipm.illinois.edu/article.php?id=424
                                    http://hyg.ipm.illinois.edu/article.php?id=354

All plant diseases are best explained by referring to the plant disease triangle.   

Picture taken from apsnet.org

In order for any plant disease to occur, you need to have a susceptible host (impatiens walleriana),disease pathogen present (downy mildew), and favorable environment (impatiens downy mildew thrives in moist conditions and cool temperatures -which can occur at night). 

If you are selling impatiens from a reputable grower and the impatiens that they have provided are thought to be "disease-free", they are not likely to be spreading the plant pathogen that causes impatiens downy mildew to customers.  Based on observations of the last several years, I believe that this disease is a problem because it has become established in the landscape.  Many landscapers/growers do not understand that if they have impatiens infected with impatiens downy mildew, they need to dispose of the infected material!  If they do not, they will continue to have further infection in the same area or at a later date.  If the removal of diseased material does not take place, this disease pathogen will be lurking in yards and landscapes, waiting to infect your and your neighbor's healthy impatiens. Many landscapers and gardeners often plant impatiens in the same area, every year. Impatiens growers are quickly finding that if they have a disease outbreak of downy mildew, they will have it the following year. 

We advise that you remove all of the diseased plant material to avoid further infection of impatiens; however, it may be difficult to completely rid the planting area of this disease and this disease pathogen is known to overwinter in the soil.  I have recently been asked the question: "If I had downy mildew of my impatiens the last two years, should I plant something else?"  My answer is "Yes". 

But, as we all know, we can have a plant disease pathogen present in our landscape, but may not have a problem, because we may not have the favorable conditions required for this plant disease to develop.  We do know that we have had favorable conditions for the infection of downy mildew to occur in Illinois in 2011 and 2012.  Unfortunately, we cannot control the weather, but we can make some predictions based on previous reports of impatiens downy mildew infection in Illinois.  We know that in 2011, we started to receive reports of this disease in the landscape in September; however, this disease was new and many may not have reported earlier disease outbreaks.  In 2012, this disease was reported in July and this is when people really started to become aware of the true devastation of impatiens downy mildew in Illinois.  Most of the 2011 and 2012 reports of downy mildew infection in Illinois were from the Chicago area.

Bed of impatiens infected with impatiens downy mildew

Based on the reports of impatiens downy mildew infection and weather conditions in the Chicago area during the last two years, I believe that there is a strong possibility that we will continue to see outbreaks of impatiens downy mildew in the future in the Chicago area. However, it is much harder to make predictions about this disease in downstate Illinois; but it is possible.  

If one decides to sell impatiens, I think that I would provide a caution statement with the impatiens explaining that your hope is to provide customers disease free material (not a total guarantee), but there is a strong possibility that impatiens could be infected by impatiens downy mildew inoculum, which could be present on infected impatiens debris/soil, lurking in landscapes.  

"Growers are responding to the gardeners requests for alternative shade tolerant plants, so do not hesitant to ask what else you could offer in leiu of impatiens." - Richard Hentschel, University of Illinois Extension Horticulture Educator

Please refer to this website for alternative to impatiens:  http://flor.hrt.msu.edu/IDM/index.htm

Impatiens leaf with sporulation of downy mildew on the underside of the leaf

(Stephanie Porter)

Significant Invasive Plant Disease and Insect Events and Noteworthy News from 2012.

First Finds & First Submissions, New Leadership & New Sites
A Look Back at Notable Events of 2012

(Taken from NPDN Newsletter:  Volume 7 Issue 11, December 2012)

Rachel McCarthy, Department of Plant
Pathology and Plant Microbe-Biology,
Cornell University

Last year ended with the announcement of some rather significant news. APHIS confirmed that boxwood blight, caused by the pathogen, Cylindrocladium pseudonaviculatum, was present in North Carolina, Connecticut and Virginia. This news created a stir in several of our labs and a buzz throughout the network, because it was the first time it had been confirmed in the United States. 

As 2012 draws to a close, let’s take a moment to reflect on some other significant events and noteworthy news from the year. In January 2012, Maryna Serdani, Department of Botany and Plant Pathology, Oregon State University (OSU), reported butternut to be a new host for thousand cankers disease and the walnut twig beetle. Suspect black walnut branch samples with signs of the disease and the beetle vector were dropped off at the OSU Plant Clinic. Scientists confirmed that the branches were those from a butternut, Juglans cinerea, and not a black walnut, Juglans nigra. The Oregon Department of Agriculture confirmed the beetles to be Pityophthorus juglandis and the OSU Plant Clinic recovered Geosmithia morbida, from the canker margins. This was the first time G. morbida and P. juglandis were detected on butternut in North America. 

On January 13, the Texas Department of Agriculture and USDA-APHIS confirmed the first detection of citrus greening in Texas. The disease was discovered in a tree in a commercial orange grove in San Juan. Texas is the second-leading state in grapefruit production and ranks third in orange production with approximately 28,295 acres in commercial citrus production in the Rio Grande Valley.

In February, APHIS announced that eight new plants – Ilex cornuta, Illicium parviflorum, Larix kaempferi, Magnolia denudate, Mahonia nervosa, Molinadendron sinaloense, Trachelospermum jasminoides, and Veronica spicata syn. Pseudolysimachion spicatum – would be added to the list of Phytophthora ramorum regulated articles as of March 1, 2012. Inaddition, APHIS moved Cinnamomum camphora species from the associated host list to the proven and restricted host list based on new information received from the state regulatory agency in California. These changes brought the total regulated hosts for P. ramorum to 137.

In early March, APHIS, in cooperation with the California Department of Food and Agriculture, expanded the regulated area for the Asian citrus psyllid (ACP) in California. The detection of ACP in San Clemente, California, resulted in expansion of the ACP regulated area to include the Camp Pendleton area of San Diego County. APHIS applied restrictions on the interstate movement of regulated articles from the expanded regulated area that are parallel to the intrastate quarantine that had been previously imposed by CDFA. ACP is considered to be present only in some areas in California and subject to official control via parallel State and Federal quarantines. 

On March 16, APHIS announced a revised Federal Order to expand the regulated area in Florida for Guignardia citricarpa, the causal agent of citrus black spot (CBS). Due to additional detections of CBS during ongoing surveys by APHIS and the Florida Department of Agriculture and Consumer Services, Division of Plant Industry, the regulated area was expanded by eight sections in Collier County and 31 sections in Hendry County. 

Later in March, the Ohio Department of Agriculture confirmed boxwood blight in Lake County in Ohio and plant pathologists at the Connecticut Agricultural Experiment Station identified Pachysandra terminalis as a new host for this disease.

The California Department of Food and Agriculture confirmed the state’s first detection of huanglongbing, or citrus greening on March 31.

APHIS launched the new Hungry Pests website in April and announced that the month will be dedicated to sharing information about the threat invasive plant pests, diseases and harmful weeds pose to America’s fruits, vegetables, trees and other plants — and how the public can help prevent their spread.

On May 24, Agriculture Secretary Tom Vilsack announced that the U.S. Department of Agriculture will support 321 projects in all 50 states, plus American Samoa and Guam. The 2012 Farm Bill submissions aim to prevent the introduction or spread of plant pests and diseases threatening U.S. agriculture and the environment.

On June 15, APHIS announced the first detection of South American palm weevil (SAPW), Rhynchophorus palmarum, in the state of Texas. APHIS previously confirmed the detection in Alamo, Texas on May 3. This detection was the result of a multi-state delimitation survey initiated in response to detections of SAPW in California in 2011. 

On May 11, 2012, a second SAPW was detected in the same general geographic area of Alamo, Texas. Both detections were found within 5 miles of the U.S.–Mexico border. In July, regional access to data within the National Repository was opened up to several users across the NPDN network. This level of access provides users the ability to view reports, maps and charts for their entire region. One of the greatest benefits of regional access is the daily first submission by state e-mail report. This e-mail report represents pest/pathogens by state that have been uploaded to the National Repository as confirmed for the first time.

On July 20, the Connecticut Agricultural Experiment Station and the Department of Energy and Environmental Protection announced that the emerald ash borer (EAB) was detected in Prospect, CT. On August 29, EAB was again found by the Kansas Department of Agriculture and USDA staff during a survey being conducted as a result of the July 2012 confirmation of emerald ash borer in Platte County, Missouri.

On August 6, Dr. Jeff Jones, SPDN Director and Professor of Plant Pathology at the University of Florida,assumed the role of NPDN Executive Director and on September 1, Dr. Marc Fuchs, Associate Professor of Plant Pathology and Plant Microbe-Biology at Cornell University officially replacedDr. George Hudler as the NEPDN Director.

In October, the British environmental secretary announced a ban on the importation of all ash into the U.K. as reports of trees showing symptoms of ash dieback disease caused by the fungus Chalara fraxinea have popped up across the country. Ash dieback disease has been moving across mainland Europe with countries like Denmark reporting losses of up to 90% of their ash trees. In February 2012, ash dieback disease was found in British nursery tree stocks, but the new reports in October represented the first occurrence of the disease in a natural area in the UK.

Spruce Windbreak Problems

Norway Spruce, Richard Webb, Self-employed horticulturist, Bugwood.org

Every year, I receive many questions on spruce windbreaks.  These windbreaks appear to be declining either due to disease, spider mites, environmental issues, cultural issues, or all of the above.  First of all, we always suggest that you submit a sample of the affected branches to our Plant Clinic for an analysis.  For more information, you can go to the U of I Plant Clinic website:  http://web.extension.illinois.edu/plantclinic/  If you have questions about your problem or the sample process, you are always welcome to call (217) 333-0519.

Spruces are generally native to cooler regions and are adapted to cold conditions. They prefer full-sun locations with acidic and well-drained soils. Improper planting techniques as well as plantings in inadequate sites can be detrimental to spruce health. When exposed to unfavorable cultural or environmental conditions, spruce can become stressed and more susceptible to diseases and pests. 

Recently, we released a U of I Plant Clinic Report on Spruce Problems (Pest and Cultural Issues). 

It includes pictures and brief descriptions of spruce cultural issues as well as the most common disease, insect, and spider mite problems that affect spruce each year in Illinois.  It can be found at the following link:  http://web.extension.illinois.edu/plantclinic/downloads/Plant%20Clinic%20Report%20Spruce.pdf

Next, if you continue to have problems with windbreaks, please go to the Illinois Windbreak Manual, which can be found at the following link:  http://web.extension.illinois.edu/forestry/iwm_complete.pdf 
This manual is a great resource.  Some of the helpful information that I often pass on to others from this manual:

• Most Illinois windbreaks will only last 40 to 50 years.  Once they mature, they can decline and lower branches can die.

• Thinning a closely spaced windbreak needs to be done to promote individual tree formation and to discourage death of lower branches.

• It is not good to plant entire windbreak to one species.  Monocultures can encounter serious problems with disease and insects pests and lack of variety of texture.

• Same species should be planted in the same row - minimize shading problems for trees that don't grow as quick as neighboring trees in adjoining rows.

• Remember to maintain, care, and protect your windbreak!

-Control competing vegetation
-Control disease and insect
-Protect from grazing livestock
-Correct Pruning
-Fertilize
-Replant or renovating windbreak when necessary

Emerald Ash Borer - Illinois First Detector Tree Pest Program

 

 The Emerald Ash Borer (Agrilus planipennis), or EAB, has been gradually making its way across the continental US since 2002. This beetle has killed millions of ash trees to date and poses a threat to all communities where ash grows. Originating from Asia, these small, green jewel beetles pose a serious threat to ash trees across the states. EAB has been reported in Canada as well as Michigan, Illinois, Indiana, Iowa, Kentucky, Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Wisconsin. The EAB has a 1-2 year lifecycle. Adult females lay eggs on the tree and within 1-2 weeks the larvae emerge and bore through the bark and into the cambium. This is the nutrient-rich area just under the bark. Larvae feed laterally around the tree, girdling it and preventing nutrients from travelling up through the tree. Signs of infestation start with thinning of the upper canopy. Up to half of the canopy may be destroyed after a few years of infestation and the tree may be killed after about six years. Epicormic shoots will appear in the branch collars of the tree and around the base. EAB prefer to attack stressed or damaged trees, but will also infest healthy trees. Due to the severity of the problem, much is being done to prevent the spread of EAB. There are many public ad campaigns discouraging people from moving wood out of the county of its origin to reduce the spread of this and other borers. Federal and State agencies as well as Universities are working with the public to prevent the spread of the Emerald Ash Borer.
 (Rachel Kirchoefer and Phil Nixon)

Early detection and response is key to managing invasive pests. The Illinois First Detector Workshops are aimed at improving first-detector training and invasive species awareness. Plan to attend these workshops focusing on current and emerging invasive forest pests in Illinois. Each location will have sessions devoted to the emerald ash borer, thousand cankers disease, and invasive plants. In-depth training sessions will highlight identification, symptoms, management, and much more!

Registration for this program will be handled by various University of Illinois Extension host sites.  You can easily register via the Extension links and contacts listed below. 

February 12 – Springfield, IL –Springfield Extension Office

Hosted by University of Illinois Extension Logan-Menard-Sangamon Unit

Register at: https://webs.extension.uiuc.edu/registration/?RegistrationID=7542

(Registration will be open until February 5^th.)

Contact:  Jennifer Fishburn- fishburn@illinois.edu

February 26 – Moline, IL -Deere-Wiman Carriage House

Hosted by University of Illinois Extension Henry-Mercer-Rock Island-Stark Unit

Register at: https://webs.extension.uiuc.edu/registration/?RegistrationID=7407

(Registration will be open until February 26^th.)

Contact:  Martha Smith -smithma@illinois.edu or Tracy Mulliken- tmully@illinois.edu

March 7 – Mt. Vernon, IL –Jefferson County Extension Office

Hosted by University of Illinois Extension Bond-Clinton-Jefferson-Marion-Washington Unit

Register at: www.extension.uiuc.edu/bcjmw

(Registration will be open January 22nd until February 28^th.)

Contact:  Chelsie Keene- ckeene@illinois.edu

March 14 – Collinsville, IL – Collinsville Extension office

Hosted by University of Illinois Extension Madison-Monroe-St. Clair Unit

Register at: http://web.extension.illinois.edu/mms/

(Registration will be open January 7th until March 8th and cash, check, and charge accepted.)

Contact:  Sarah Ruth- ruth1@illinois.edu

March 21 – Champaign, IL – Champaign Extension Office

Hosted by University of Illinois Extension Champaign-Ford-Iroquois-Vermilion Unit

Register at: http://web.extension.illinois.edu/cfiv/

(Registration due by March 18th. No refunds after March 20^th.)

Contact:  Sandy Mason- slmason@illinois.edu

March 26 – Lemont, IL- Midwest Golf House (*FULL)

Hosted by University of Illinois Extension Cook County

Register at: http://extension.illinois.edu/go/treepest

(Registration will be open December 1st until March 17th.)

Contact:  Greg Stack -gstack@illinois.edu

April 4 – Lemont, IL- Midwest Golf House

Hosted by University of Illinois Extension Cook County

Register at: http://extension.illinois.edu/go/treepest

(Registration will be open until March 26th.)

Contact:  Greg Stack -gstack@illinois.edu

A $25 registration fee covers on-site lunch and training materials. No registration at the door. If you do not cancel prior to the workshop, and do not attend, there is no refund.

All workshops 9:00 AM - 3:00 PM

*Each Workshop is worth

4.0 Continuing Forestry Education Credits

4.25 Continuing Education Credits (CEU’s) for IAA Certified Arborists

Questions:  Contact Stephanie Porter at satterle@illinois.edu

Honeylocust knot or galls - Call for more research

Question: "I was wondering if you know of any treatment for Honey Locust Knot? Or what is your suggestion to deal with that problem. I have a client that has 7 Honey Locust tree's that are clearly infected with this Knot" -Arborist from Maryland

Picture of a honeylocust sample received at the U of I Plant Clinic with galls on branches.

Picture of a honeylocust sample received at the U of I Plant Clinic with galls on branches.

You recently emailed Nancy Pataky with a question about honeylocust knot.  She is now retired and she has forwarded your email to me.  Honeylocust knot can be tricky, as to my knowledge, the cause has not been proven by research.  In my recent investigation on this topic, I have found that there could be many different causes for “knots or galls” in honeylocust.  You first need to rule out chemical/herbicide use near these trees.  For example, the herbicide, Imprelis (no longer sold), has been found by Midwest plant diagnosticians to cause knots in honeylocust.  Insects and bacteria are also some other causes for honeylocust galls.

We rarely see these honeylocust galls in Illinois, but when we did, we did not find any evidence of chemical or insects in the galls; therefore, Nancy Pataky suspected a bacterial cause.  She wrote about this topic in the U of I Home, Yard, and Garden newsletter:  http://hyg.ipm.illinois.edu/pastpest/200805a.html . Nancy Pataky’s theory of bacterial (Pseudomonas savastanoi) formed galls was based on research from the Ohio State:  http://ohioline.osu.edu/sc189/sc189_55.html . If you read this bulletin from the Ohio State, they had reports of this disease mainly in the Midwest, but also in Maryland.  The spread of the bacterium was thought to be caused by the lack of sanitation during hand pruning and the trees eventually died.  In this newsletter article, Nancy Pataky mentions that a plant pathology student at the Ohio State was beginning a new project on this problem; however, we have since learned that the funding was lost. 

We have an Agdia plant diagnostic listserve, a great resource for plant diagnosticians across the US to discuss problem plant samples. Here are some recent posts about honeylocust galls:

“Several years ago (2003ish) while working in Maryland, we found galls on honeylocust.  I'm surprised that this link is still active, but you can look at some images:  http://www.mda.state.md.us/sc/plants-pests/plant_protection_weed_mgmt/new_pest_detections_md_nurseries_-s2.php .  We called it honeylocust gall or knot.  The problem was on Shademaster and Skyline honeylocust and we found it both in the landscape and at a nursery.  It was present on the landscape trees for multiple years and eventually killed many of the trees.  At that time, I did some research and there was an article on the internet that suggested that Pseudomonas savastanoi was the cause.  I sent samples to Ohio State.  I do not know if they ever confirmed if this was the cause or what the status of the research is at this time.”

Another plant diagnostician that had a honeylocust sample with galls reported the following on the diagnostic listserve: “We had a similar case and could not rule out gall midge.  An entomologist thought it might be Neolasioptera brevis, but we had no direct evidence.” 

Since the release of Nancy Pataky’s article, I have received inquiries and reports about galls on honeylocust.  For example, a Canadian plant diagnostician has reported, “We had one honey locust sample came in the middle of July showing exactly the same gall symptoms. After one month's moist chamber incubation, some Lepidopteran larvae (Family Pyralidae,snout moths) came out from the galls. I have seen reports on locust twig borer (Ecdytolopha insiticiana) but our entomologist insisted that what we got were not the same.”

Therefore, if we are not sure of the cause, we can’t be sure of a treatment.  I would suggest that you send a sample to your local Plant Clinic.

I would also suggest that you rule out chemical/herbicide issues.  Next, I would try to cut into a gall and check for signs of insects.  If you suspect that this is a bacterial induced gall problem, please be sure to sanitize your pruners after each cut.   I am sorry, but, unfortunately, I have no other management suggestions besides keeping the tree in good health by fertilization and watering during times of drought.   

Please let me know if you know of any recent research done on honeylocust knot or gall. 

Stephanie Porter