Plant Diseases: Wrap Up

Delve into all the things that can go wrong with your plants via diseases of all types (bacteria, parasites, water molds, nematodes, fungi, and viruses), and the built-in arms race between predator and prey that keeps balance.

Plant distortions and diseases

Getting Started

Diagnose sick plant symptoms, and figure out what to do about it.

Sick Plant Symptoms
Sick Plant Resources
Sick Plant Clinic
Back to School – Plant Diseases (Aug 2012)
Plant Diseases Update (Oct 2012)
Finished Plant Diseases! (Dec 2012)

Plant Diseases

Learn about the main categories of plant diseases, and deep dive into examples of them all.

Plant Diseases – Bacteria Fire Blight   Crown Gall
Plant Diseases – Flowering Plant Parasites Mistletoe   Lichen (not a disease)
Plant Diseases – Water Molds Downy Mildew   Sudden Oak Death
Plant Diseases – Viruses Tomato Leaf Curl Virus (TYLCV)   Grape Leafroll Associated Virus (GLRaV)
Plant Diseases – Nematodes Root Rot Nematodes   Spiral Nematodes
Plant Diseases – Fungi Black Spot of Rose (Ascomycetes)   Cedar-Apple Rust (Basidiomycetes)

Plant Diseases in Action

Head into the field to experience plant diseases all around us in the garden and nature.

SOD Blitz 2013
SODMAP App
SODBlitz Partnership
Mushrooms
Mistletoe in Bend
Clear Lake Plant Diseases
Discriminating Squirrels (Feb 2016)
Summer on the Iron Horse Trail (July 2019)

Books and Movies

Read about plant diseases and plant pathology, and enjoy films where plant diseases play a role.

Five Kingdoms
Essential Plant Pathology
All That the Rain Promises and More ...
Winter Movies 2013: Nausicaa of the Valley of the Wind
Rosemary & Thyme: And No Bird Sings (Jan 2019)

Thanksgiving

Finally – it is Thanksgiving Eve, and I have one thing on my mind – turkey dinner! And mashed potatoes, stuffing, gravy, cranberry salad, and sweet potatoes. And, maybe pumpkin pie with whipped cream. OK, so I have a lot on my mind. I love this time of year – the traditions, trying something new, counting my blessings (and considering that some hardships may be a blessing in disguise).

Waiting for the turkey

Thinking of turkey, reminds me of a lunch-time walk out in Dublin, California last year. At the time, I was researching street trees through the seasons. It was fall – warm in the sun, bright blue sky, golden-brown leaves, and chilly around the edges. I spotted a herd of turkeys on the sidewalk ahead, but they seemed to scatter. I strode on. Gradually I became aware of a click- click sound behind me. I walked faster. The sound continued – click-click. I hurried on as the sound increased – click-click. I whirled around to find the herd of eight to ten turkeys following me, with the click-click of their claws on the pavement.

Part of me found this endearing – they were like baby ducks or geese, imprinted to follow anything that moves. Another part of me had the irrational thought that these birds are actually dinosaurs. Remember the scene in Jurassic Park where the cute, chicken-like dinosaurs with flaring hoods bring down a man by blinding him, then attacking him en masse? Luckily, I escaped.

I plan to enjoy my turkey dinner this year, enjoy the people around me, and thank God for the blessings and trials of life!

Cedar-Apple Rust (Basidiomycetes)

Cedar-apple rust (Gymnosporangium juniperi-virginianae) is caused by a fungus in the Basidiomycota phylum. The disease life cycle involves two types of trees – apple or crab apple (Malus genus), and red-cedar or juniper (Juniperus genus). The apple or crab apple is an aecial host (the host plant on which heteroecious rust fungus produces aecia and pycnia); and the red-cedar or juniper is the telial host (the host plant on which a heteroecious rust fungus produces telia, and sometimes uredinia).



Telial gall of cedar-apple rust on cedar, with spore horns withered after spore germination. Photograph courtesy C. W. Mims from the APS slide collection, Introduction to Smut and Rust Fungi.

Some vocabulary, because this is complex:

• Aecia – the fruiting body of a rust fungus in which the first dikaryotic spores (aeciospores) are produced. Aeciospores infect the alternate host (in this case, the juniper). Dikaryotic spores have two sexually compatible haploid nuclei per cell and divide simultaneously.
• Pycnia – the flask-shaped haploid fruiting body of a rust fungus bearing receptive hyphae and sexual spores.
• Telia – survival spore, or teliospores, produced by rust fungus in which germination occurs.
• Uredinia – asexual dikaryotic, often rust colored spores, capable of infecting the host species on which it is produced.

Basidiospores form on the germinating teliospores of a red-cedar or juniper gall. The basidiospores infect apple leaves to produce pycnia. Aeciospores are produced in blisterlike aecia on the lower surface of the apple leave. The aeciospores infect junipers only (not the apple tree). The disease is monocyclic, meaning one life cycle per growing season (versus polycyclic which is even more complicated)!

For management tips, see the Integrated Pest Management (IPM) site. Prevention is the best strategy – remove junipers that are within five miles of apple orchards, and avoid planting junipers near apple trees in the landscape (although damage is not extensive to apple trees, except in very wet years). Because the disease is monocyclic, you can effectively apply fungicide applications timed to protect the apple trees during the time when basidiospores are released. Plant apple and crabapple trees that are disease resistant.

Black Spot of Rose (Ascomycetes)

Black Spot of Rose (Diplocarbon rosae) is caused by a fungus in the Ascomycetes phylum. It is frequently found on rose bush leaves here in the Bay Area, especially during the winter or in the fog belt. Symptoms include black spots and yellowing on the upper surface of leaves. The fungus produces ethylene, which induces chlorosis (yellowing) of the leaves, and eventually abscission (leaf drop). Ethylene is a growth regulator that affects leaf drop, fruit ripening, and plant senescence; and can cause vascular wilt diseases. The black spots may have a feathery margin and may include fruiting bodies (best seen with a hand lens). Inside the fruiting body, microscopic sexual spores called ascospores are produced in sacs called ascus (pl. asci), and released upon maturity.

The fungus requires water to reproduce and grow, and can survive in fallen leaves and infected stems. Overhead sprinklers may keep leaves wet for long periods of time, and may splash the fungus from infected to uninfected plant material.

Black Spot of Rose, with chlorosis. Photo courtesy of C. Ash, available by APSnet via License to Copy.

For management tips, see the Integrated Pest Management (IPM) site. Prevention is the best solution – plant resistant rose bushes in a sunny location with plenty of room for air circulation; remove fallen leaves and infected plant parts; and do not let moisture stay on the leaves for more than seven hours. This means you should avoid watering with overhead sprinklers; and, if you spray the leaves to remove dirt or pests, do so early in the day so the leaves have a chance to dry. You can manage black spots on leaves using a combination of bicarbonate of soda and horticultural oil, or using Neem oil or fungicides.

Plant Diseases – Fungi

Fungi are the last category of plant diseases in our year-long study of plant diseases that can affect our plants in the San Francisco Bay Area. Other categories have included bacteria, plant parasites, water molds, nematodes, and viruses. Our resources have included information from my plant diseases course at Merritt College in Fall 2012, Essential Plant Pathology, and Five Kingdoms. As with other categories, many fungi are beneficial for the ecosystem, but others can cause disease or damage.

Fungi are incapable of producing their own food, so seek nourishment from dead organic matter or living plants. Fungi are composed of filaments, which excrete enzymes that decompose organic matter so that the cells can absorb the nutrients. An individual filament is a hypha (hyphae), and the mass of filaments is the mycelium. Some parasitic fungi produce toxins that help them invade a host; others produce mycotoxins that are poisonous, causing illness or death to animals or humans who ingest them.

White mycelia of a wood decay fungi - great on the forest floor, on your roof - not so much.

Hypha cells contain mitochondria, nuclei, and other organelles. Nuclei are haploid (one set of chromosomes). Cell walls are made of chitin (similar to the shells of crabs and exoskeleton of insects), rather than cellulose (the main component of plant cell walls), making fungi more closely related to animals than plants. Additionally, fungi use glycogen for food storage (similar to animals), rather than starch (as plants do). The hypha may grow into survival structures (called fruiting bodies) that produce spores, such as puff balls, mushroom, and conks. Fungi reproduce by sexual and asexual spores. Sexual spores ensure genetic diversity and adaptability; asexual spores are clones that ensure survivability.

The four major phyla of true fungi are Ascomycota, Basidiomycota, Chytridiomycota, and Zygomycota. The phyla are called true fungi to distinguish them from organisms that were formerly classified as fungi, such as the water molds (or Oomycetes). The first two groups are especially important for plant diseases:

• Ascomycetes – bread and beer yeasts, morel mushrooms, and plant parasites that cause common diseases such as Chestnut blight, apple scab, leaf spots, Dutch Elm disease, post-harvest diseases, powdery mildews, and vascular wilts
• Basidiomycetes – root rots, rust fungi, smut fungi, wood decay fungi, turf grass diseases, and Sclerotium spp. blight

All parts of a plant—roots, stems, vascular system, trunks, flowers, and leaves—are susceptible to fungal diseases.

Cal at Mountain View Cemetery

I recently took the “UC Berkeley’s Blue and Gold” tour at the Mountain View Cemetery in Oakland. We visited the gravesites of some of the famous and infamous folks, buried in the cemetery, who have some connection to Cal. The Mountain View Cemetery tours are offered twice a month – the standard tour on the second Saturday of the month, and specialty tours—like the UC Berkeley tour—on the fourth Saturday. Docents lead the tours, telling fascinating and well-researched stories.

Henry Durant (1802 - 1875)

Some of my favorites include Reverend Henry Durant, the founder of the College of California, which later became the University of California. He and his advisors decided not to create a Christian college, but rather one based on Christian principles. Another is Joseph LeConte, who was one of the first professors at the U.C. Berkeley, hired to teach geology, natural history, and botany. He was a friend of John Muir, a frequent visitor to Yosemite, helped co-found the Sierra Club, and has a glacier in Southeast Alaska named after him. LeConte’s headstone is a boulder from Yosemite. His brother John LeConte also taught science at the university, and is buried in the cemetery.

Julia Morgan (1872 - 1957)

 

Bernard Maybeck’s remains are in the Urn Garden; he taught engineering drawing at Cal, designed the Hearst Gymnasium for Women, and mentored Julia Morgan. Julia Morgan, also a Cal alumna, has a simple grave marker that includes the names of her parents and siblings. Apparently, she didn’t want a fancy headstone – “my work speaks for itself.” She worked with William Randolph Hearst to create Hearst Castle.

Charles Franklin Doe (1833 - 1904)

 

Charles Franklin Doe, who is buried in “Millionaire’s Row,” donated funds for the Doe Memorial Library at U.C. Berkeley (he was inspired by the library of Alexandria). Anna Head (of Head-Royce School fame) is buried here, as is Ida Louise Jackson (an African-American daughter of slaves who attended U.C. Berkeley to obtain her teaching degree in the 1920s).

Ida Louise Jackson (1902 - 1996)

 

I recommend this tour, or any tour offered by Mountain View Cemetery. It is a great way to spend several hours on a Saturday morning – surrounded by beautiful scenery, and in great company!

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.