Essential Plant Pathology

For a great resource for learning about plant diseases, I recommend the text book we used for the Plant Diseases class at Merritt College last fall. Essential Plant Pathology was written by Dr. Gail L Schumann and Dr. Cleora J. D’Arcy, and published by American Phytopathological Society Press in 2010 (Second Edition).

It is not your standard text book, in that the text is very accessible (except for a few deep-dives into genetics), and it is filled with graphics, photos, case histories, high-level summaries, references, web resources, and a CD, all of which are great for visual learners. Case histories, called Disease Classics, appear throughout the text, and describe Host, Pathogen, Symptoms and Signs, Disease Cycle, Management, and Significance. A glossary and index help the reader grapple with new concepts and terminology.

The presentation is organized around plant diseases from the five kingdoms – fungi, bacteria, animals, plants, and protoctista, as well as viruses and environmental factors. The idea is that by understanding the phylogeny of organisms, you can use the information to identify the pest or disease, understand its life cycle, and use the knowledge to mitigate the problem. The book’s emphasis is on learning a system for diagnosing plant diseases, rather than memorizing many plant diseases.

 

Trees of Lakeside Park

On a recent field trip to the Gardens at Lake Merritt, we discovered a wonderful collection of mature, established trees at Lakeside Park. Most of the tees have ample room in which to grow, so they have been able to spread out and grow naturally. Trees add so much to the environment, so their presence is pleasure enough. But to the gardener, this is a wonderful resource for viewing the natural form of a tree, its true size in its later years, and its transformation throughout seasonal cycles.

When planting a tree from a five gallon bucket, it is easy to be enamored with its physical qualities as seen in close up photographs of bark and flower, but much more difficult to envision how tall a 60-80 feet tree really is! Seeing trees in situ can help when you’re selecting a tree for your yard, or envisioning how your current landscape may change over the next decade or two.

Cork Oak	Bonsai
Dawn Redwood (deciduous)	 Monkey Puzzle Tree
 Wine Palm	Young Olive

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Many of the trees are not native to the Bay Area, but they are beautiful trees worthy of study and appreciation. Many of us have some of these trees in our yards, or access to them in parks, so it helps to see good, healthy specimens. For trees like the Wine Palm, which has been over harvested, parks like this help preserve tree specimens until they can be restored in the wild. For  trees like the Monkey Puzzle tree, which was greatly coveted during the plant collection frenzy of the Victorian era, parks provide a glimpse into the past. I recommend a stroll through Lakeside Park to see its trees in any season.
 

The Gardens at Lake Merritt

I heard about the Gardens at Lake Merritt last year from a Tree ID classmate while attending Lake Merritt College. My fellow student raved about all the gardens located close to Fairyland by Lake Merritt. I’ve been around Lake Merritt a few times, and thought I had seen the Gardens, but my gardening buddy, Ruth, and I decided to see if we had missed something. Recall that we are visiting Bay Area gardens to study their design, plantings, infrastructure, and winter charms. Turns out, there is a gem of a garden complex at 666 Bellevue Avenue in Oakland.

Instead of a single garden, we discovered a series of gardens, almost like the garden rooms we read about from garden history. We only had a couple of hours, so we tried to see as much as we could in a quick survey. Some high-lights include a tiny, serene Japanese garden, and an extensive Bonsai collection (most of the deciduous trees were without leaves, so you could appreciate their foundational forms, but one apricot was already in bloom). We enjoyed the Rhododendron collection from all over the world, and the subtropical Vireya Garden (Vireyas are a kind of Rhododendron, from the mountains and jungles of Philippines, Malaysia, Indonesia, and New Guinea). The Palmetum is a wonderful collection of unique palm trees, ferns, and cycads. The succulent collection near the Easterbrook Fountain has many fine examples of succulents, and cacti. There is a Bay Friendly garden, a community garden for children, an Edible garden, a Pollinator garden, and a Sensory garden, all worthy of more exploration.

  Palmetum

 Japanese Garden

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Golden State Bonsai Collection

Vireya Garden

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The gardens are being restored, and always in need of volunteers. The Lake Merritt Pruning Club, among other groups, helps with the trees. The day we visited, a team of volunteers was adding organic matter to the beds near the Easterbrook Fountain. This is a great local treasure to visit, or help tend! I’m looking forward to returning in the spring when blossoms emerge, and in the fall to see the leaves turn color. Learn more: http://gardensatlakemerritt.org/
 

Sick Plant Clinic

Another great resource for diagnosing plant problems in the San Francisco Bay Area is the Sick Plant Clinic held at the University of California Botanical Garden in Berkeley the first Saturday of the month (always good to check the calendar). The clinic is free.



Bring in your container plant or plant part for evaluation. (Cover the plants and disease samples in containers or bags before entering the Garden to protect other plants). Microscopes, reference books, and plant and insect experts are available for consulation. Expect to be grilled with questions about the plant symptoms and the plant environment.

Leaf miner trail to the left, and woolly aphid cocoon to the right (partially obscured by the stem).

The symptoms may vary with the seasons. I visited the Sick Plant Clinic in October. We saw rust on a pear leaf (pome/juniper rust); leaf miner trails and a woolly aphid cocoon on an apple leaf; a leaf distortion on a Chilean Coyote Bush; scales on a citrus leaf; sun burned Jasmine leaves; and black sooty mold on Bay leaves. I’m planning to visit again in the spring for a glimpse of diseases that manifest as the weather warms and plants start to bud.

Sick Plant Resources

Thanks to the Internet and the World Wide Web, we have many resources for identifying plant diseases available at the click of a button. Following are some of my favorites.

American Phytopathological Society

The APS is a nonprofit professional, scientific organization dedicated to the study and control of plant diseases. Search their online database for symptoms such as “leaf spot” or “leaf spot on roses.” Their online store offers many scientific books related to plant diseases. Visit: www.apsnet.org

Integrated Pest Management

The University of California Agriculture and Natural Resources provides the statewide Integrated Pest Management Program, hosted by U.C. Davis. IPM is a process for solving pest problems, while minimizing risks to people and the environment, in urban, agricultural, and wild land or natural areas. Find out about all kinds of pests and how to combat them (or co-exist with them). Visit: www.ipm.ucdavis.edu

Forest and Shade Tree Pathology

This site is described as an online textbook for those learning forest and shade tree pathology, and is hosted by the University of New York College of Environmental Science and Forestry. Even though it is “East Coast”, it is a great resource for “West Coast” and San Francisco Bay Area plant diseases. Visit: www.forestpathology.org

Tom Volk’s Fungus of the Month

This site is a treasure from Tom Volk, hosted by the Department of Biology at University of Wisconsin at La Crosse. The last post is August 2010, but the site is full of great pictures and information about fungi. The presentation is old school HTML, but the photos are useful, and the information is engaging. Visit: http://botit.botany.wisc.edu/toms_fungi/

Online Glossary at Cornell University

This site provides a glossary of technical terms in plant pathology and is hosted by Cornell University. Search alphabetically to access the definition, pronunciation, and a drawing or photograph. For example, navigate to the C section to look up “canker” and see a picture and hear it pronounced. Visit: www.plantpath.cornell.edu/glossary/

Sick Plant Symptoms

This time of year, a lot of plants look a little sick. Deciduous trees have lost their leaves, and look barren, or maybe even dead. Evergreen broadleaf trees still have their leaves, but most look pretty battle scarred. Leaves exhibit spots, necrotic tissue, or even missing sections. Some of this is residual from the previous season, and may be less apparent with spring growth. Often these symptoms are unsightly, but do not pose a risk for the plant; they simply indicate current or past environmental conditions. Sometimes the symptoms do indicate a more serious problem that should be treated, or the plant removed.

When you start diagnosing a sick looking plant, take some time to check it and its surrounding site for symptoms and clues:

• Look at the leaves for spots, mold, sun burn, yellowing, and necrotic patterns. But don’t just look at individual leaves; look for patterns in the plant or tree canopy. Is one leaf having the problem, a group of leaves, or all the leaves?
• Do some branches look dead? If so, is it just one branch, a scattering of branches, or a whole section of the canopy?
• Is the bark intact? Are there cankers high on the trunk, or low near the soil line? Does the trunk flare and visible root structure look healthy?
• Did the symptoms occur all of a sudden, or did they occur gradually over a period of time? Are they related to seasons?
• What is happening in the area around the plant? Are nearby plants experiencing the same thing? If so, are they plants of the same species, or of different species?
• What site events have occurred in the last several years – construction, landscaping, broken irrigation system, fertilization mishap, flooding, extreme weather (freezing or drought)? Symptoms for some problems manifest several seasons or years later.

Flagging (dead branches) may indicate blockage in the vascular system.	Black Spot of Rose is very common in roses, especially late in the season.
Cankers low on the trunk may indicate environmental damage, or below-ground diseases.	Conks feed on dead wood, indicating this tree is dying, and may become a hazard.

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Try to identify the plant by its scientific name. Many plant diseases are very specific to a particular species, so knowing the plant name can help you research the specific disease. It is also useful to be familiar with some of the diseases common in the San Francisco Bay Area; for example: powdery mildew, downy mildew, rust, anthracnose, black spot of rose, peach leaf curl, wilt, water molds, and sudden oak death are very common in the area. Armed with your site research, scientific plant name, and basic awareness of symptoms in your area, you may be able to identify the plant disease or environmental condition that produced the symptoms you are seeing.
 

Winter House

One wing of Ruth’s Folly is known as Winter House, a kind of greenhouse where the tenderest plants overwinter. The structure is typically covered with landscape cloth, but during the winter months it is covered with visqueen and warmed naturally by the sun and artificially by a heater.

Winter House from outside.

From the outside and backlit by the sun, Winter House looks a like an underwater aquarium or a science fiction movie set. But inside, it is cozy and inviting, with the morning sun streaming in through the windows.

Winter house from inside.

The two Ruths and I appreciated stepping out of the crisp morning air and into its warm interior before starting our tour of The Ruth Bancroft Garden. Several succulents were blooming, including a Euphorbia and several aloes.

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After our tour, we ended up in Winter House, which also doubles as the gift store. The enclosure had become quite warm between the heater and the sun, and the Euphorbia blossoms were glistening with nectar. We enjoyed the heat, light, and fragrance while making our selections from the gift store (including bulbs from The Ruth Bancroft Garden private collection and breeding program).

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Shady Ideas in Winter

When I visited The Ruth Bancroft Garden in the summer of 2011, I was taken with the long arbor, which provides shade for tender succulents in the hot sun (see Shady Ideas). Under the arbor grows a border, planted with succulents, cactus, and Mediterranean plants in keeping with the garden’s theme. I was just as taken with the winterized version of this arbor, which is transformed with visqueen into an “other-worldly” green house.



Exterior view of the winterized arbor.

In this protected environment, plants grow, bloom, and carry out their normal life cycle. Recently the Garden obtained the special rocks they use to construct raised garden beds. The crushed rocks, mixed with organic material and soil, provide the good drainage these plants require. The rocks are native - quarried locally near Mount Diablo. With the reworked garden beds and the protected environment, the tender border thrives through the winter.

Inside view of the protected greenhouse.

During our docent-led tour, with no exterior views to distract us, we could focus on the variety and details of the plants before us. Some plants were blooming, or preparing to bloom; some exhibited beautiful color variations; some looked like they belonged in the ocean; and some looked like creatures out of an old Sci Fi movie!

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