A Trip to Muir Woods and the Effect of Phytophthora ramorum (Sudden Oak Death)

Thanks to the National Plant Diagnostic Network (NPDN) meeting, I was able to make my first trip to California.  In addition to some awesome, diagnostic workshops and meetings, we were able to choose one of four field trips/tours.  It was a very, hard decision, but I chose: Phytophthora ramorum-Redwoods Tour-
Marin County.

Basically, on the this tour, we were taken to the site where Sudden Oak Death (P. ramorum) was first discovered in the United States.

"Since the early 1990s, oaks and tanoaks have been dying in the coastal counties of California. Since then, other types of plants have been found to be infected or associated with this disease, referred to as Sudden Oak Death (SOD), ramorum leaf blight or ramorum dieback. Phytophthora ramorum is the pathogen that causes these diseases. Sudden Oak Death was first reported in 1995 in Mill Valley (Marin County) on tanoak. Since that time, the pathogen has been confirmed on various native hosts in fourteen coastal California counties (Marin, Santa Cruz, Sonoma, Napa, San Mateo, Monterey, Santa Clara, Mendocino, Solano, Alameda, Contra Costa, Humboldt, Lake, and San Francisco), and in Curry County, Oregon. Through ongoing surveys, APHIS-PPQ continues to define the extent of the pathogen’s distribution in the US and limit its artificial spread beyond infected areas through quarantine and a public education program." -USDA-APHIS

Case Study: Sudden Oak Death /ramorum blight caused by Phytophthora ramorum

This tour included a visit to Muir Woods!

There is an abundance of information and stories that could come from Muir Woods, but the one I would like to share is that of the trees located there.  The large live trees located at Muir Woods mostly consist of coastal redwoods; however, there are some scattered Douglas Firs there.  The tallest coastal redwood stands 258 feet tall ("A six foot person stacked 45 times").  The average coastal redwood is 600 to 800 years old and the oldest is 1200 years old. -Now, that is old!  In the understory of these magnificent trees are tanoaks.

Unfortunately, many of the tanoaks in Muir Woods are infected with Phytophthora ramorum or SOD (Sudden Oak Death). Most of the trees are dying. To a plant pathologist the story may end here.  We took many pictures, so that we would have record of the symptoms of tragedy, in the hope that we can catch it before it enters our State, like Illinois.  What I did not realize, is how much this disease is affecting the ecosystem of Muir woods.

Note the dark, cankers on the tanoaks, which are symptoms of Sudden Oak Death caused the the fungal pathogen, Phytophthora ramorum.   For more information, go to:  http://www.suddenoakdeath.org/

If the tanoaks die-then there are no acorns...
If there are no acorns, then there will be no food for the forest rats.....
If the forest rats have no food, then they could possibly die, and then the endangered spotted owls will have no food....

And so, there are many ecological studies taking place to study the many ecosystems, like this one at Muir Woods.

In most of the pictures, the browning foliage belongs to dying tanoaks in Muir Woods.

I wish I could end my story here, but the horror of it is, this fungal disease pathogen,  P. ramorum, not only affects oaks, but also has been found to infect over 200 plant hosts and counting....
http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files/usdaprlist.pdf 

Here is how you can prevent the spread of this pathogen to your "neck of the woods": http://www.aphis.usda.gov/publications/plant_health/content/printable_version/SBR_StopTheSpread.pdf

Greenhouse Poinsettias with Pythium root rot

When these plants were examined, the roots appeared to be rotted.  When the root tissue was examined under the microscope, there were oospores present.  This is a sign of Pythium root rot.  The visual symptoms of the poinsettia roots also appeared to be those associated with Pythium root rot at various stages of infection.

Pythium can be introduced to plants by infested crop debris in the greenhouse, transplanting infected cuttings, or recycling potting mix or containers.  In addition, in some cases, this pathogen can be introduced by contaminated irrigation water.  The problem could also be that the potting medium is not draining properly.  Remember, environmental conditions can cause soils not to dry out properly. 

This disease is favored by high soil temperatures.  Another thing that seems to favor this disease is high soluble salts in the root substrate.  I also read where excess fertilization can promote the growth of Pythium.

Good sanitation is the best defense against this disease.  Make sure that the potting mix is sterile and disinfect work surfaces.  Unfortunately, once Pythium infection takes place, control of the pathogen can be very difficult.  Disease development can be reduced by lowering pH to 5.5 or below; however, this can cause nutrient disorders to develop in plants.

There are fungicides that can be used to help manage this disease.  In Illinois, the Commercial Landscape and Turfgrass Pest Management Handbook lists fungicides that can be used for root rot. You can also refer to the report on disease to find out which fungicides are used against Pythium: 
http://ipm.illinois.edu/diseases/rpds/615.pdf

A preventative fungicide application may be necessary the following year, in addition to improved sanitation.


Other very, helpful links:
http://ncsupdicblog.blogspot.com/2011_01_01_archive.html
http://www.negreenhouseupdate.info/index.php/diseases/296-poinsettia-pythium-root-rot
http://www.gpnmag.com/Don%E2%80%99t-Expect-Pythium-Root-Rot-to-Always-Act-the-Same-article2958
http://www.chasehorticulturalresearch.com/pages/ChaseArticles/45PythiumRootRotonPoinsettias.pdf

Downy Mildew on Impatiens in Illinois

In October, 2011, there were several reports of downy mildew on garden impatiens (Impatiens walleriana).  This disease was first reported in the U.S. in 1942, but recently several sources say this disease has been confirmed on impatiens in coastal southern California, northeastern Illinois, northern Indiana, Cape Cod in Massachusetts, Long Island and upstate New York. If you think that you experienced this disease in your garden, there are no worries of it infecting other plants.  However, it is very, important that you remove and destroy infected plants.  There is still a chance that this disease pathogen could overwinter and infect impatiens the following year.  I have read that New Guinea impatiens have resistance to this disease and can be a considered a choice that can be planted in an infected area.  End of the season fungicides are not recommended.  Watch for this disease next year! Keep a careful watch on impatiens and catch this disease in the early stages and remove infected plants immediately!  Fungicides can provide some protection, but will not protect impatiens for the entire season.


Several weeks ago, we received an email from from Diane Anderson saying that this downy mildew had infected most of the impatiens at the University of Illinois Trial Gardens.  In the next several pictures you can see just how devastating downy mildew can be, if impatiens have been infected.

Symptoms of downy mildew of impatiens have been described as: "yellowish or pale-green foliage, downward curled leaves, leaf distortion, white to light-gray fuzz on leaf undersides, new leaves that are small or discolored (yellow or pale green), flowers buds that fail to form and stunted growth".

 The plant pathogen that causes downy mildew is an oomycete and is spreads by oospores as seen below.

For more information on Down mildew of impatiens, you can check out the following websites:

Downy Mildew causing problems on impatiens in the Landscape

Check impatiens for downy mildew

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