In the 1990's, a mysterious illness was discovered both along the western coast of North America and in Europe. The sickness affected foliage, trunks, and overall health of many genera and species of woody plants, resulting in death or serious damage. Since its first official reporting in 1995, much research has been undertaken to identify its source, spread, and effective treatments, and there is now cause to believe there will be a sizeable resurgence in the disease due to the emergence of a more evolved strain.

This organism develops spores on leaves of primary host species, including the California Bay Laurel, which then are carried by rain and/or air currents to the leaves of the new host, where they continue to develop. Other host genera or species include Rhododendron, Madrone, Huckleberry, Buckeye, Bigleaf Maple, Toyon, Manzanita, Coast Redwood, Douglas Fir, Coffeeberry, and Honeysuckle. Once in contact with the host plant, the organism then infects the inner bark and sapwood of affected plants, resulting in bleeding cankers. Affected trees and shrubs typically die as a result, either from the disease itself or from other pests or diseases that attack the weakened plant. After infected plant matter dies and decomposes, the organism is transferred to the soil, where it germinates until another host species takes up spores. Phytophthora ramorum can overwinter in soil, and will also take advantage of already wounded trees and shrubs.

A phosphonate compound is the chosen preventative, life-extending treatment for high-value trees. Trees and shrubs that are not highly valued, however, are best left to their own devices. If kept otherwise healthy, they may survive for a while before succumbing to the pathogen. The best way to deal with this issue, as with most landscape diseases, is to prevent it from occurring in the first place. 

The best way to prevent Sudden Oak Death from killing landscape plants is to prevent it from entering the garden, because once it is there, it is not possible to eradicate it. The first step in preventing SOD is to inspect nursery plants before bringing them home. Many commonly grown ornamental plants available at nurseries can be carriers of the pathogen, and the state-established regulations we have do not always catch infections. Carefully inspect leaves of host plants for symptoms, which include browning and spotting of foliage. Do not purchase any plants with these symptoms. After bringing plants home, quarantine them away from the garden for eight weeks before installing. Some nurseries will use general fungicides on their plants to prevent spread of many diseases, and the symptoms of SOD can be masked. This quarantine time will increase the likelihood that an infection will be caught before the new plant is added to the landscape.

Trees affected by Phytophthora ramorum are prone to rapid decay and unpredictable failure. If an infected tree is growing close to homes or other structures, sometimes the best option is removal. Always consult local regulatory officials before deciding to remove trees, as sometimes permits are required. If there is an acute emergency, contact the city arborist or your local fire or police department.

Although there are many host plants for Sudden Oak Death, removal of these plants to prevent spread is not recommended at a residential level. If there is a healthy, susceptible-species Oak tree in the landscape, removal may be helpful to prevent spread, especially if there are few other host species planted nearby. Otherwise, leave host plants where they are.

Responsible disposal of infected plant debris and subsequent transportation of infected plant parts can be a cause of more areas in our state becoming affected by the pathogen. Even after being removed from the host plant, branches, leaves and twigs can still harbor Phytophthora ramorum. The best disposal method is to leave debris on-site, chipping small material for use as groundcover and using larger pieces for firewood. Removal of plant debris from the infection site is only recommended if it is the first infected tree in the area, or if the presence of debris on the property is a potential fire hazard. If infected tree parts are removed from the property, make sure whoever disposes of them does so inside the same quarantine area.

Finally, if infected trees or host plants are removed, they can be replaced with trees and shrubs that adapt well to the site. If another Oak tree is desired, make sure to choose a species that is not as affected by Phytophthora ramorum, such as those in the White Oak group (Valley Oak, Garry Oak, or Blue Oak).

A recent project undertaken by Dr. Matteo Garbellotto at the University of California Berkeley campus in conjunction with other contributors fueled SOD Blitzes, information from which was used to create a comprehensive Google Earth map overlay. The map overlay is available for download on the project's website. This 2024 survey found that infection levels are on the rise in the state of California, and have the potential to rise even more in early 2025 due to our wet winter weather. It also concluded that Sudden Oak Death is spreading quickly due to the emergence of a new strain of the pathogen.

The original pathogen, which was of the N1 lineage, has been surpassed in infectiousness and aggressiveness by the new N2 lineage. This new lineage has the ability to be more successful in warmer temperatures, which is a looming issue in California due to both climate change and the warmer weather of our Central Valley. Given these outlooks, it is of utmost importance that the public become aware of this disease and learn all they can about its spread, including how property owners can discourage it from entering their landscape.

To learn more about Sudden Oak Death, review the following questions:

What is the connection between Sudden Oak Death (SOD) and nursery plants?
As with many other pests and diseases that affect landscape plants, SOD is spread by human activity via the transport and sale of nursery specimens. All host plants for the disease are strictly regulated in California, and must be inspected and approved for transport and sale prior to shipment out of the regulated area they originate in. Purchasing of host plants at nurseries should be done carefully; all should be inspected before a sale is made. Inspect the leaves of host plants for symptoms, and refrain from planting host species near susceptible Oaks in the landscape. It is recommended that no host species be planted within 150-1,000 feet of susceptible Oak species. For an updated, comprehensive list of SOD host species, visit suddenoakdeath.org.

How do I determine if my tree has Sudden Oak Death?
It is a bit difficult to determine whether a tree is affected by SOD or another disease or pest. Homeowners are not equipped to diagnose trees on their own with absolute certainty. However, there are some steps that can be taken to determine whether it is a likely cause of tree decline:

• Find out what type of tree you have, and whether it is a susceptible species. Although the disease is called Sudden Oak Death, it does not affect all Oak tree species equally. In California, SOD mainly affects Tan Oak, Coast Live Oak, Shreve Oak, Canyon Live Oak, and California Black Oak.
• Determine if you are in an infested zone. There are many maps available to the public, including one on the Board of Forestry and Fire Protection website. Keep in mind that even if your property is not located within a designated infested zone, it is still possible, though a bit less likely, that your tree is infested with Phytophthora ramorum.
• Compare the symptoms of SOD with those exhibited by your tree. Make sure to check any host species nearby for symptoms, as well. If plants located close to your Oak are showing SOD symptomology, it is more likely that your tree could be suffering from it as well. Symptoms range from browning or dead foliage to spots or discoloration on leaves, cankers on trunks, and general dieback.

How do I pronounce Phytophthora ramorum?
The fungus-like organism that causes SOD, Phytophthora ramorum, is pronounced fye-TOFF-thor-rah  rah-MOR-um.

If my Oak has SOD, what are the chances that it will die?
There isn't a great way to determine whether a tree will die as a result of the disease, as each tree responds differently to infection. Even trees of the same species, planted in the same yard can exhibit different symptoms. For the most part, however, once infected, Tan Oaks have a relatively high probability of being killed. Coast Live Oaks have a somewhat lower probability of being killed. Most of the time, infections are a death sentence for susceptible species.

If I suspect that my tree has SOD, who should I hire to treat it?
The California Oak Mortality Task Force (COMTF) regularly carries out trainings for tree care professionals in the state. A list of training participants can be found on their website (suddenoakdeath.org). Hiring a professional who is familiar with the progression and treatment of SOD is key to ongoing health in affected plants. 

If I cut down my infected Oak tree, what should I do with the debris and wood?
The easiest way to deal with infested wood is to leave it on site. The wood can be chipped and used as mulch, and larger pieces can be used as firewood. Doing this will not significantly worsen the local disease conditions. Do not move any infected wood or plant parts out of the infected area; this will increase the spread of the disease to more locations in our state, and possibly lead to the destruction of large swaths of forest. As a general rule of thumb, it is not recommended to pile up wood next to established plants of any kind, as pests tend to 'jump' from wood piles to living trees and shrubs. Composting infected plant parts is not recommended, as most home-created compost piles do not reach high enough temperatures to kill the pathogen.

What plants can be installed to replace a tree killed by SOD?
If a new tree is desired to replace the lost one, choose a plat that suits your needs and that will adapt well to the planting site. If another Oak tree is the best choice, make sure to select a species that is not as affected by Phytophthora ramorum, such as those in the White Oak group (Valley Oak, Garry Oak, or Blue Oak). Also, take care when choosing new plantings for underneath Oak trees; many ornamental plants are carriers of the pathogen, and have the potential to affect nearby Oak trees. For a comprehensive list of host species, visit suddenoakdeath.org.

Ah, Euphorbia pulcherrima. The quintessential ornamental plant found in so many homes over the holiday season. These plants hail from Mexico and Central America, and are members of the Euphorbiaceae plant family, making them relatives of Croton, Castor Oil Plant, Cassava, and Rubber Tree. The plants were first discovered back in 1834, and derive their common name from the first United States minister to Mexico, Joel Roberts Poinsett. In fact, the day of his death (December 12) is now celebrated as National Poinsettia Day in the United States. Poinsettias have also been historically known under the names Mexican Flame Flower and Painted Leaf.

In 1919, an urban legend caught fire which told of the account of a two year old being poisoned to death after consuming a single Poinsettia leaf. Solely on this basis, the plant was included in H. R. Arnold's 1944 book Poisonous Plants of Hawaii. The author admitted that the inclusion was completely based on hearsay, but that did not stop the United States Food and Drug Administration (USFDA) from circulating a publication stating completely erroneously that "one Poinsettia leaf can kill a child". All attempts to prove this toxicity scientifically have failed, however, and it is widely considered to be a safe indoor plant to keep around children and pets.

These shrubs or small trees are semi-evergreen (they generally lose most of their leaves during the cooler months of the year), and produce very small yellow flowers that are grouped together at the center of colorful bracts. These bracts are most commonly seen in bright red, but can also be pink, creamy white, variegated with multiple colors, or orange. The bracts are often mistaken for flower petals, but are actually modified leaves, colored to attract pollinators to the inconspicuous flowers.

In order for bract color to emerge brightest, these plants require some special treatment. Bract color is created through photoperiodism, which essentially means that they need long periods of darkness over a few months' time to attain their color. It is recommended that plants are kept in complete darkness for twelve to fourteen hours each day over 6 to 8 weeks for best results. In most cases, this treatment is done by growers, but for those green thumbs who keep their Poinsettias alive throughout the year for display during the holidays, this is a task that will need to be completed at home.

Poinsettias are popular holiday decor in homes, churches, offices, and elsewhere across the United States, thanks to their ease of care, bright coloring, and a strategic marketing campaign by California grower Paul Ecke Sr. In 1923, he founded the Ecke Ranch, which today provides almost 80 percent of the plants bought and sold in the United States each winter. It may (or may not) be surprising to hear that Poinsettias are actually the most commonly purchased plant in the United States, with 35 million plants sold in the six week period leading up to Christmas. Having so many plants to choose from can be a bit confusing, however, so we've come up with some guidelines for purchasing these popular holiday ornamentals.

As with many plant purchases, investigating plants for health is an important step. The first indicator of a healthy Poinsettia is leaf health. Look for plants that have leaves which are a rich, dark green. Plants that have issues will exhibit leaves with burned edges, pale coloring, yellowing, curling, spots, or physical damage. These indicators can point to plant stress caused by cold temperatures, watering issues, or nutrient deficiencies. Bracts (the uppermost leaves that exhibit bright colors) should be unblemished and fully colored, without spots, curling, cracking, tearing, or dried sap.

Watering is a second major indicator of plant health. When a Poinsettia plant is picked up, it should be heavy, but not have water dripping from the bottom (unless it has just been watered). If pots are too light, make sure to check for signs of water stress (which typically exhibits itself in leaf issues, as discussed above). Heavy, overwatered pots can also cause plant stress; leaves can be wilted and yellowed due to overwatering. A plant with medium hydration is best.

Finally, choose a plant that is good lookin'! Poinsettias naturally have a handsome shape to them, and are bushy with a good amount of foliage. When looking for a perfect Poinsettia, think about the place you will be displaying it. Placed in a corner? On a narrow step? In the middle of a table? Depending on the display site, you may want to grab a plant that is a bit triangular, one-sided, or rounded.

Poinsettias are considered to be easy-care plants, and when brought home should be placed in a spot that receives full sun. They can take direct sun, especially indoors. Poinsettias should be put in a spot that is not drafty; they prefer temperatures stay between 65 and 70 degrees Fahrenheit. Keep plants well-watered but take care to not overwater or have standing water around the roots. Many Poinsettias sold around the holidays have beautiful coverings around their containers for aesthetic purposes, but these coverings can cause issues when watering. They do not typically have drainage holes in them, so the water that drains out of the base of the container is captured and held, creating a situation where plants can easily drown. To water plants with coverings, make sure to remove the covering before watering, and allow excess water to drain off before replacing it.

Poinsettias in their first month outdoors should be placed in a shaded spot that is somewhat sheltered. As new growth continues to emerge, pinch it back to encourage a bushier plant to form. Over the next few months, care for the plant in its outdoor space, gradually introducing it to more and more light over time. Provide enough water to keep soil relatively moist, but not waterlogged. At around Labor Day, or as soon as nighttime temperatures begin to drop, bring the plant back indoors. Make sure to quarantine the plant away from other houseplants for a while after it is brought inside until it is clear that it has no pest or disease issues. To initiate blooms, Poinsettias will need to be exposed to between 12 and 14 hours of darkness starting six to eight weeks before the holiday season. To do this, place a box over the plant or place the plant in a dark closet. Return plants to a sunny location (one that receives between 6 and 8 hours of sunlight each day) inside a window during daytime hours when they are ready for display.

Ensure that plants get potted up about once every two years or so, depending on how quickly the root ball is growing. As a general rule of thumb, when roots start to poke out from the bottom of the pot, it is a good time to pot up. Poinsettias will continue to grow larger and larger over the years, and will be at a great size within 5 years to be planted outdoors. Make sure to harden off plants by exposing them to increasing amounts of time outdoors over a few weeks before leaving them out in the garden permanently to avoid transplant shock. The final planting site should receive direct sunlight, have well-draining soil, and be somewhat sheltered from drying winds. Another option is to grow Poinsettias outdoors in containers, so that they can be brought indoors over the cooler months of the year.

Now that you know more than you've ever wanted to know about Poinsettia plants, you're ready to care for one of your own!

​Happy Holiday Gardening.
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