SOD Blitz Partnership

I love the idea of the SOD Blitz partnership between the UC Berkeley science community, the USDA Forest Service, and “citizen scientists” to gather data on Sudden Oak Death. A similar idea has been used to gather information about migration of birds, butterflies, and fish. It also reminds me of the crowdsourcing projects run on the web, using members of the online community to solve complex problems.

Tip blight symptoms on tanoak caused by P. ramorum. Photo by Joseph
O'Brien (Creative Commons Attribution 3.0 License).

SOD Blitz participants are trained to look for symptoms, and to conduct testing on  specimens. The SOD Blitz project website provides information on training dates, symptoms, testing, and meetings.  The 2014 Spring SOD Blitz is currently being organized, so the training schedule has not yet been published. If you are interested in participating in a Blitz, check the website regularly for updates. In the meantime, there are plenty of workshops and lectures scheduled for Fall 2013.

SODMAP App

A free SODMAP application, with SOD Blitz research information, is available as a plugin to Google Earth. It can be installed on the desktop or on smart phones (Android and iPhone). The application shows you visually where SOD Blitz specimens were taken, and the test results. SODMAP categories include infected and uninfected trees, oaks, tanoaks, and water samples.



SODMAP application running on a desktop computer. Click on an icon to drill down to detailed information.

Icons on the map represent either a single record for one of these categories, or multiple records. Drill down to view detailed information, or to see multiple records and their details. Some trees are tagged, and checked every year. Others are sampled randomly from year to year.

This icon indicates a SOD infected tree - here a bay laurel (Umbellularia californica).

On smart phones with GPS, you have the added capability of the app identifying where you are, and automatically displaying details for your surroundings. This is great if you are out in the field. Currently I have SODMAP running on my desktop and iPad, and really enjoy scoping out the results of the San Francisco Bay Area SOD Blitz. 

The icon indicates a SOD infected oak or tanoak tree - in this case live oak (Quercus agrifolia).

SOD Blitz 2013

I recently attended a lecture at University of California, Berkeley (UC Berkeley, or Cal) by Dr. Matteo Garbelotto, to summarize the results of the 2013 SOD Blitz. Dr. Garbelotto is an adjunct professor at UC Berkeley. He received his B.S. and M.S. degrees in Forestry from the University of Padua, Italy, and then completed his graduate and post-graduate work in forest pathology at UC Berkeley. He has been studying SOD since its discovery in California, and is an engaging speaker, making information accessible for both scholar and community. Fittingly, the lecture was held under a mature oak tree outside Tolman Hall on the UC Berkeley campus.

SOD Blitz—or Sudden Oak Death Blitz—refers to an event where professionals and trained “citizen scientists” join forces to fan out over Northern California, look for evidence of Sudden Oak Death, and gather specimens. The specimens are tested and analyzed in the lab. In this way, a lot of field data has been gathered in the last six years to study the introduction and spread of SOD in California. Data is published online, and available via a free app for Android or iPhone. Professionals include USDA Forest Service and the UC Berkeley Forest Pathology and Mycology Laboratory. SOD Blitz also refers to community outreach to inform the community about Sudden Oak Death.

Symptoms of ramorum leaf blight on California bay laurel. Photo by Joseph
O'Brien (Creative Commons Attribution 3.0 License).

Several items interested me. In general, the overall infection rate of tanoaks and live oaks decreases after a dry year, and then spikes after a wet year. However, a comparison between 2012 and 2013 research shows some deviation - increases were observed in two colder areas, and decreases in hotter areas. This supports observations that the disease operates differently between coastal forests and inland forests. Infestation typically happens during the spring rains (March, April, May), and not the early rains in November, December, January, February), so you should avoid pruning during spring rains.

Plants such as bay laurel, Rhododendron, and Camellia are intermediate hosts for Phytophthora ramorum; removing them from the presence of a high value oak can reduce chances of its infection. Use of phosphonate to treat healthy oaks is very promising, but they are reevaluating delivery mechanisms, since plugs may cause damage to the trees. Additionally, Dr. Garbelotto observed that the disease is relatively slow moving, which is giving scientists a chance to study it. These lectures are offered periodically and well worth your time.

Clear Lake Plant Diseases

I’m afraid my Plant Diseases class from Merritt College in Oakland has despoiled me – I am always on the lookout for plant diseases! End-of-summer is a great time to spot them, as many plants have spent their reserves on reproduction, and are more vulnerable to attack. Here are some of the diseases I spotted in Clear Lake; oaks seem especially hard hit.



Sudden Oak Death –  I wasn't close enough for direct inspection, but this looks like SOD from afar; caused by the water mold, Phytophthora ramorum. 

Oak Gall – these little "nipples" are galls caused by asexual reproduction by the oak gall wasp.
When the wasp lays its eggs, hormones kick off a type of genetic engineering to create the perfect nursery (the gall).

Oak Apple Gall – this "strange fruit" indicates sexual reproduction by the oak gall wasp.

Tent Caterpillar – we found these gauzy structures all over foliage.
The residents had already moved on.

In many cases, these diseases do not cause permanent damage. An organism is simply taking advantage of a situation, and working through its own life cycle. After the class, seeing plant disease is not necessarily alarming. Plants in nature are rarely perfect; instead, they are teaming with all sorts of life forms. Learning to enjoy the whole ecosystem of a plant, both good and bad, can add to the enjoyment of nature as well as the garden. And raising your tolerance for imperfection can lower the need to combat the imperfect with pesticides.

Sudden Oak Death

The plant pathogen Phytophthora ramorum, commonly called Sudden Oak Death (or SOD), is a water mold in the Oomycota class. I reported on Sudden Oak Death a couple of years ago as part of a series on oak trees. Most Phytophthora species are soil-dwelling, root pathogens, but P. ramorum is a leaf pathogen. Spores from the leaves and twigs of infected trees spread to an oak through water, wind-driven rain, plant material, or human activity. Once the spores are on the oak, microbes use natural openings to access bark tissues. The microbes kill cells, causing bark cankers, clogged water and transport systems, leaf die-off, and ultimately death of the tree. Take a look at SOD zoospores: http://youtu.be/rTo6UwnZiQg

Fascinating to me is that P. ramorum has a wide host range (including tanoaks, and non-oaks, such as California bay laurel, Rhododendron, and Camellia), but these hosts are not killed by the pathogen. Oaks, on the other hand, are considered terminal hosts; when they encounter the pathogen, they may become infected very quickly in the right conditions. According to the IPM, the best predictor of the disease is the presence of a California bay laurel.

Since there is no cure, prevention is the best way to manage Sudden Oak Death. Purchase non-infested nursery plants from a reputable dealer; remove infected oaks following local ordinances; remove non-oak hosts (such as California bay laurel); and dispose of infected plant debris properly (leave on the property as mulch or compost). The IPM website lists using phosphonate fungicide treatments (Agri-Fos) as a preventative measure. The treatment must be made on healthy trees, and repeated every year or two, so it is recommended for high-value trees.

Downy Mildew

Downy mildews are water molds in the Oomycota class that affect foliage. Downy mildew appears on the upper leaf as a yellow, discolored section between veins, and on the lower leaf as white or purple-brown mold. (Downy mildew is not the same as Powdery mildew, which is a fungus that appears on the upper leaf as a white powder). Downy mildews flourish in moist conditions, between 40 – 60 degrees F, so are prevalent in some areas of the San Francisco Bay Area. The Downy mildew microbes are obligate parasites, meaning that they need a living host, so their strategy is to feed, but not kill, the host plant. Frequent hosts include grape, cucurbits (pumpkin, cucumber, etc.), and impatiens.

Powdery mildew sporulation on alfalfa leaves.
Photo by Gerald Holmes. This work is licensed under a Creative Commons
Attribution-Noncommercial 3.0 United States License.

The Downy mildews require water for infection, and at last 90% humidity for sporulation. The pathogen exists as an oospore in leaf debris or soil between growing seasons. When conditions are right, the spores germinate and produce sporangia (tree-like structures), which in turn produce zoospores (swimmers with flagellum, capable of motility in water). The sporangia and zoospores are airborne, or splashed onto lower leaves. The spores enter stomata or damaged tissue on the underside of the leaf, and infect the leaf (generally within 8 – 12 hours). Additional waves of sporangia and zoospores follow during the growing season as a secondary inoculation. The mold that you see on the underside of the leaf is the sporulation, or collection of spores. At the end of the season, sexual reproduction produces oospores that can survive without a host until the next growing season.

Downy mildews are typically host specific, meaning that a particular pathogen attacks a specific host (if your pumpkin exhibits Downy mildew, you do not need to worry that it will jump to your grapes; however, the same environmental conditions may exist, making your grapes susceptible to their own Downy mildew pathogen). For management tips, see the Integrated Pest Management (IPM) site, and search for a specific host. In general, recommendations include planting disease-resistant seeds and plants; rotating crops with plants that are not susceptible to the pathogen; and using practices to minimize leaf wetness. Chemical control methods are also available; consult the IPM for recommendations about your particular host.

Plant Diseases - Water Molds

For our next group of diseases that attack plants, I’m reporting on Protoctistas, or “water molds”. They are in the Eukarya Super Group, and the Oomycota classification. For references, I am using Five Kingdoms, Essential Plant Pathology, and information from my plant diseases course at Merritt College taught by Dr. Ann Northrup in Fall 2012.

Oomycetes were classified as fungi, but later reclassified as Protoctista, since they are more closely related to brown algae. Oomycetes do resemble fungi in that they have filamentous hyphae used for feeding. However, at a cellular level, they do not have cross walls between nuclei; they are composed of cellulous; and their nuclei are diploid (two sets of chromosomes). In contrast, fungi have cross walls between nuclei; are composed of chitin (similar to crabs); and their nuclei are haploid (one set of chromosomes). Water molds are very primitive, and require moist conditions for reproduction. The asexual spores, called zoospores, have flagella and are motile, enabling them to move through moist conditions to a target such as a root. Take a look: http://youtu.be/jQXO4P8cpQQ
  

Two types of Oomycetes are found, both of which affect plants in the San Francisco Bay Area:

• Root affecting – water molds that live in garden soils, ponds, and streams
• Foliage affecting – water molds that live above ground, and are adapted for air dispersal (but still require moist conditions)

A water mold disease caused the Irish potato famine in 1845 – 1852. Closer to home, a water mold is behind Sudden Oak Death in the San Francisco Bay Area. Other water molds cause downy mildews and white blister rusts.