Effort Underway to Establish Pathogen Resistant Lupines at Milagra Ridge

Over 1,000 summer lupines are being planted at Milagra Ridge this spring. The newly planted seedlings are all protected by cages and flagged according to species, source, and propagation center. Christina Crooker / Golden Gate National Parks Conservancy

April 2019 - As Mission blue butterflies decline at Milagra Ridge, silver lupines at the site are also in rough shape. They are losing their leaves and flowers to a fungal pathogen identified in 2010 as Colletotrichum lupini. Silver lupines are host plants for Mission blue butterflies; Mission blue caterpillars depend on their leaves for food. To help buffer the Mission blue population from pathogen outbreaks going forward, the Golden Gate National Parks Conservancy is planting over 1,000 summer lupines at Milagra Ridge this spring. This lupine species is also a Mission blue host plant native to the region, and crucially, it is resistant to the problematic pathogen.

Still, experience has shown that summer lupine seedlings grown in a nursery and transplanted into the field do not do very well. So, in addition to planting all of those seedlings, Conservancy scientists are leading an experiment to figure out how to establish summer lupines from seeds. They are testing three different ways of preparing the seeds, and two different ways of planting them. The preliminary results are exciting. Germination rates along transects at Milagra Ridge so far show that putting seeds in a rock tumbler may be more effective than nicking them, or soaking them with a bit of coffee before planting. In addition, burying the summer lupine seeds seems like it may be a slightly better planting method than raking them into the soil. The final results will help restoration specialists establish the pathogen-resistant summer lupines more widely at Milagra Ridge, and at other restoration sites throughout the parks, in the years to come. The hungry Mission blue caterpillars of tomorrow may be depending on it.

Contact Christina Crooker to learn more.

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