The best environment for laurel trees has morning sun and water for most of the year.

Laurel has expanded its range to grasslands and other sub-optimal areas, making them vulnerable to staphylococci.

When many kinds of woody plants are stressed like this giant redwood, they will attack them.

Courtesy of Themis J. Michailides/UC IPM

Botryosphaeria is commonly found in woody plants such as walnut trees, and is newly found in laurel trees. Look for dying leaves at the tips of the branches.

For many years, a latent cell in our native laurel tree, a pathogen called Botryosphaeria, has been in a low position, waiting for the tree's defensive ability to launch an attack. It's now.

For many years, the Gulf Laurel has been a free exercise. They are overpopulated in the best places with water for most of the year and spread to drier grasslands and shrubland. The normal fire cycle may culminate fire-sensitive saplings, but we have prevented fires from playing a regular role in the management environment. Therefore, after being established in wet years, the laurel tree survived the early drought and grew. Now, they are big trees and need water very much. At the same time, this year’s drought has gone from drought to terrible drought, from extreme to abnormal.

Botryosphaeria is a genus of fungi. They are opportunistic pathogens associated with stress, which can cause canker and blight in many woody plants. They are also endophytes, which means they live in the host and usually do not cause damage.

"We call it'robots' for short," said Steven Swain, Marin and Sonoma's environmental gardening consultant. "Bots infect seedlings and live with plants forever. Unless the plants are stressed, the robot will not cause any bad consequences. They just wait for a surprise attack. It infects many species and has a variety of hosts because there is always something Under pressure."

Drought-stressed woody plants are typical hosts of Staphylococcus. But the same is true for plants far from their native habitats—such as laurels on grasslands or giant sequoias planted on well-watered, warm lawns.

"Bots don't care about the pressure on the plants," Swain said. "Bots attack when plants are stressed. When you see the branches of the Novato sequoia withered, it may come from Bots. The shaded branches of madrones and manzanitas get it because they need plenty of light."

However, the Bot in the Gulf Laurel is new.

"I rarely saw it on laurel trees in the past," Swain said.

Swain said that if you see a laurel tree with dead branches, it may be the target of robot attacks, not just drought stress.

"If the laurel tree is under drought stress, you will see that the small tip leaves are still alive, while the old leaves will dry out and fall," he said. "If this tree is infected with a Bot, you will see a branch die from the top, usually a larger branch grows below. But because these symptoms can come from many sources, we collected samples."

Swain uses samples to determine if a tree has bots or other problems. Bot is a normal pathogen; it will not destroy the entire species. If something else is attacking the tree, it may need to be quarantined.

"We are not worried about bots spreading or not spreading," Swain said. "Robots are everywhere. Bot is an all-rounder."

Fungal spores are mainly spread by splashing water when it rains. When a Bot infects tissues, it forms small, black fruit structures (conidia), which may be ejected from the bark. Infected laurel trees do not always have these ulcers, but if you cut into the wood, you will see the tissues appear dark black and wedge-shaped discoloration.

Antiseptics can treat bots, but using antiseptics may not be the best idea. Instead, as part of regular fire protection maintenance, remove any dead and dry branches and focus on strengthening the plant's defense capabilities.

"When you have widespread fungi that prey on stressed plants, usually the best strategy is to focus on plant health," Swain said. "Watering is best. The point is not to let the plant flourish. Don't kill it kindly by creating warm, moist soil. Use a soaking hose to drop the water 10 inches down, and then wait to water again until it's down 10 inches dry. Only Give it enough water to keep the pressure level in the dull roar."

For more information, please visit marinmg.ucanr.edu.

Sponsored by the University of California Cooperative Promotion Department, the University of California Marin Master Gardener provides home gardeners with information based on science and research. Email questions to helpdesk@marinmg.org. Attach photos related to plant diseases and insect pests inquiries. The office does not accept temporary visits. Subscribe to the free quarterly e-newsletter flyer of the University of California Marlin Gardener Master at marinmg.ucanr.edu

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