Phytophthora Tentaculata

New disease warning!

Imagine a world without oregano. Or celery. Or sage. Or chrysanthemums. It could happen.

Sticky monkey flower plant infected with P. tentaculata (right) compared with a healthy plant. (USDA)

There is a new plant disease on the horizon. Its name is Phytophthora tentaculata.

Just because this disease is tricky to pronounce (Fie-TOF-ther-uh), doesn’t mean you should ignore it. Its name is Greek phytón (plant) and phthorá (destruction), so the name phytophthora means plant-destroyer. (The tentaculata part of the name refers to its retractable tentacles.)

First noted in Germany in 1993, Phytophthora tentaculata hitched a ride on contaminated nursery stock and made its way to Central California and Monterey County in 2012. It is still spreading and is deadly to many of your garden and landscape plants.

According to the Retail Nursery and Garden Center IPM News, Phytophthora tentaculata poses a long-term environmental and economic threat to many native and non-native plants because this pathogen can stay viable in the soil for many years. There is currently no known treatment.

What is Phytophthora tentaculata?

Phytophthora tentaculata is a member of the water mold family. Water molds fall between fungi and algae. These pathogens attack stems and roots and frequently kill their host plant. There are several types of phytophthora, including those that cause potato blight, crown rot, and sudden oak death. You cannot see these organisms with the naked eye, but watch for the symptoms and know which plants are currently considered susceptible.

Host plants

The following garden plants are highly susceptible to Phytophthora tentaculata:

• Celery (Apium graveolens)
• Hickory (Cichorium intybus)
• Oregano (Origanum vulgare)
• Sage (Salvia species)
• Tarragon (Artemisia dracunculus)

These ornamental plants are also at risk (and may harbor the disease):

• Barberton daisy (Gerbera jamesonii)
• Buck brush (Ceanothus cuneate)
• California coffeeberry (Frangula californica)
• California sagebrush (Artemisia californica)
• Chrysanthemum species (hybrids, marguerite, and oxeye daisy)
• Costus root (Saussurea costus)
• Coyote mint (Monardella villosa)
• Lavender cotton (Santolina chamaecyparissus)
• Mugwort (Artemisia douglasiana)
• Rocket larkspur (Consolida ajacis)
• Toyon (Heteromeles arbutifolia)
• Verbena species (vervain hybrids)

Symptoms of Phytophthora tentaculata

Symptoms of Phytophthora tentaculata look a lot like many other plant diseases: chlorosis, reduced root growth, root lesions, root rot, stem cankers, stem collar lesions, and stunted growth are strong indications of infection.

Preventing Phytophthora tentaculata infection

Contaminated nursery stock is the most likely way this pest will reach your garden. Good water management is the best way to prevent infection. Phytophthora tentaculata is a soil-borne disease. Spores can also stick to plants, tools, containers, and shoes. And they travel through the movement of water. Spraying an infected plant can transfer the water molds to nearby plants. Since symptoms take time to be visible, avoiding potentially infected plants is in your garden’s best interest. These tips can help you protect your garden:

• Buy certified pest- and disease-free seeds, seedlings, and plants.
• Quarantine all new plants for at least 4 to 6 weeks, including any water that may drip from the container.
• When possible, use seeds rather than plants.
• Install plants at the proper depth.
• Avoid over-watering.
• Allow soil to dry out between waterings.
• Ensure proper drainage.
• Sanitize tools, boots, and hands after handling potentially infected plants.
• Sanitize shoes with bathroom cleaner after walking through an infected area.
• Do not add infected plants to the compost pile.
• Ask nursery or garden store staff if they know about this new disease and what they are doing to prevent its spread. (You may be the person who brings it to their attention!)

If Phytophthora tentaculata appears in your garden or landscape, contact your local Cooperative Extension Office. They may have helpful advice to protect your plants. And they need to know how this disease is spreading.