Alien Invasion, Part 10:

Pampas & Jubata Grasses

Tall, waving white plumes above bunches of slender green blades make for a handsome coastal resident, right? Maybe for the uninformed, but to the many native plant lovers on the California coast, this sight is horrifying. Pampasgrass and jubatagrass are familiar sights along the coast, unfortunately. These rapidly spreading invaders are non-natives at their worst.

Jubata grass (Cortaderia jubata)

Photo courtesy of John M. Randall/ The Nature Conservatory

First introduced into Santa Barbara in the mid-1800’s for horticultural purposes, the taller of the two grasses, pampasgrass (Cortaderia selloana), originally came from South America. It was introduced into Europe in the early 1800’s and then to North America later. It was raised commercially around the Santa Barbara area, and the Soil Conservation Service even planted it in southern California for dryland forage and erosion control in the mid-1900’s.

Jubatagrass (Cortaderia jubata), with shorter bunches of slender green blades, also is native to South America. It was brought into France and Ireland first, and then somehow was introduced into North America. It probably was a horticultural import as well.

Both grasses are invasive in California’s wildlands. Both species can be found both in yards and escaped into the open spaces in Los Osos and Morro Bay. Jubatagrass is the more aggressive species. It cannot tolerate frost, and so can grow only along the coast. Drive from San Luis Obispo to the Monterey Bay area along US Highway 1, and you will see entire hillsides covered with jubata. Landslides often disturb the hillside soils and create an ideal site for propagation of invasive species. Jubatagrass threatens coastal ecosystems by crowding out the native species, particularly in sensitive coastal dunes. Jubata has invaded large areas of the central coast in Vandenberg Airforce Base. It also is a major headache in logged areas on the northern California coast.

Pampasgrass often is seen along with jubatagrass in the San Francisco Bay area and along the southern California coast. Pampasgrass, being tolerant of frost, also has escaped and invaded an inland riparian zone along the American River near Sacramento.

There are two ways to identify which plant species is which. Pampasgrass develops tall bunches of greenery that can reach over ten feet in height. The female of the species selloana also has a very white seed plume with no traces of purple color. Unfortunately, the male selloana has purple coloration, making its plumes difficult to distinguish from jubata, which also has a purple tinge. However, jubatagrass seldom reaches greenery heights of more than about five feet tall. This is probably the easiest distinction to make between the two species.

Pampasgrass has both male and female plants. In nature, selloana reproduces only by sexual means, with fertilization occurring in the presence of both male and female plants. The female plant flowers when it is about two to three years old. Originally, only the female plants were cultivated for their showier plumes. However, male plants have escaped into the environment now and allow the plants to spread in the wild.

Jubatagrass has only female flowers. However, the flowers can form viable seeds without pollination. This is called apomixis, and allows jubata to spread uncontrollably. An individual plume can produce 100,000 seeds, and large clumps of jubata can produce one million or more seeds. Viable seeds can be produced in the first year of growth. The seeds can be carried by the wind for up to 20 miles. This makes jubata extremely aggressive in wildlands. In both species, the grasses usually flower in late summer or fall.

Burning or grazing cannot control these South American grasses. They simply re-sprout too quickly. Mechanical digging and cutting can be used with tools such as the Pulaski (axe on one end and hoe on the other) or mattock (pick on one end and hoe on the other) being effective. However, the task can be very tedious and time consuming until skill is developed. Also, the steep, rocky hillsides on which the plants can be found are dangerous to traverse and can require skilled mountaineering techniques to be employed. The plant and the upper roots have to be detached and inverted to prevent re-sprouting. Once plants have flowered, it is important to burn or compost the plumes to prevent seed dispersal.

Post-emergent chemical control can be used on both pampasgrass and jubatagrass. For homeowners, Roundup at 2-4% may be effective if applied in the fall and sprayed until the leaves are wet. Rope-wick applicators can be used with undiluted Roundup to eliminate spray drift. In all cases, a surfactant should be added to enhance absorption. Other registered herbicides include Poast, Fusilade, Prism and Stalker or Arsenal. Once plants have been killed, clumps can be mechanically uprooted and left to decompose naturally. Leaving dead clumps in wildlands may prevent new seedlings from being established.

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