Developing Pathogen Risks and Native Here Nursery

Some of you have heard the KQED story on a new invasive species—Phythophthora tentaculata. This is in the same genus as the organism that causes sudden oak death (SOD). P. tentaculata is a root rot pathogen and is spread by infected plant material, water, and soil and was recently responsible for a swath of dieback in an San Francisco Public Utilities restoration project. Back in December, Diana Benner, along with Alisa Shor, Kristen Hopper and me, put on a symposium to address this new risk to our wildlands. The seven most recent videos on the CNPS-Santa Clara Valley Chapter YouTube page contain most of the content of the symposium. We have re-started the California Native Plant Nursery Network and plan on continuing to share resources, knowledge, and emotional support to work through this and future issues.

What has Native Here Nursery done in response?

Charli Danielsen already had good growing practices in place. Our material is sourced locally, and primarily from seed, reducing introduction vectors. Additionally, we have our stock on benches above the ground, with relatively inhospitable wood chip mulch underneath. We are also growing near a location of known Phythophthora ramorum (SOD) infection, Tilden Park. As such, we are inspected for P. ramorum on a monthly basis and have not yet had a positive sample among our nursery stock. Native Here also lacks a greenhouse, which can act as a year-round breeding ground for pathogens. Those are good things, but we need to get better.

“Kitchen clean” is a simple way to think of it. The ground should be considered infected, and our potting benches and plant cages need to be kept clean. Native nurseries, including Native Here Nursery (NHN), must stop sharing dirty pots. This has been identified as one of the likely vectors for several pathogens. We strive to minimize waste, and re-using pots are a good way to do that, so we need to develop an effective and efficient method for cleaning pots. We are also looking into the possibility of sterilizing our soil medium prior to potting-up, and re-thinking foot and vehicular traffic into the nursery (other possible vectors).

This will cost more money for nurseries and will result in the need for additional infrastructure at NHN. Please contact me if you have ideas for funding/grant opportunities for infrastructure projects—e.g. plant benches, watering system for propagation areas, soil containment structure, etc.

A question now becomes: how clean can we expect to be? Will putting container plants into restoration sites come with a risk of invasive pathogen introduction? I have had many conversations with nursery, restoration, and regulatory organizations these past three months, trying to come up with answers and solutions. In tandem with cleaner growing practices, I am exploring alternative ways to support restoration efforts that may reduce infection risks, and could have side benefits as well (think on-site, or even in situ restoration nursery). Email me if you are interested in talking about this.

Keep in mind that native plant nurseries are not the only vectors of pathogens. Grading and other construction equipment, nearby gardens/communities, and latent pathogens that rear their heads with environmental disturbance or the addition of water. Then there is the issue of the primary introductions,. I believe that we can point to the standard horticultural industry as the main factor in importing new pathogens; they have been dealing with exotic pathogens for a long while now.

Some of these widepread pathogens, such as Phythophthora cinnamomi, P. cactorum, and Pithyum spp., can be expected reside somewhere at NHN. I look forward to using trusted procedures and to finding new ways to continue to produce clean nursery stock for the local urban/wild interface of the East Bay.

Theo Fitanides, Native Here Nursery manager

Mount Diablo manzanita (top) and oak mistletoe (bottom). Photos by Kevin Hintsa.