Source: California Invasive Plant Council
URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=50&surveynumber=182.php
Invasive Plants of California's Wildland
|Scientific name||Ficus carica|
|Common name||edible fig, common fig|
|Synonymous scientific names||none known|
|Closely related California natives||0|
|Closely related California non-natives:||0|
|Listed||CalEPPC List A-2,CDFA nl|
|By:||John M. Randall|
HOW DO I RECOGNIZE IT?
Edible fig (Ficus carica) is the familiar fig tree that produces edible fruits sold fresh, dried, and as paste used as filling for cookies (fig newtons) and other sweets. Mature trees often have multiple trunks and may grow to thirty feet tall. The heavy trunk and branches are covered with a smooth, light gray, flaky bark. The sap is thick, sticky, and slightly milky. The leaves are rough to the touch, bright green, with three to five lobes, the classic fig-leaf shape. They are two to eight inches wide and two to ten inches long with a two- to four-inch-long petiole (stem). Edible figs are deciduous, dropping their leaves in mid- to late autumn and leafing out again in early spring (March-April). The fruits are shaped like small sacks full of sand, two to four inches long and nearly as wide. Edible fig has been widely cultivated, and the color of ripe fruits of different cultivars ranges from dark purple-black in the ‘Mission’ fig to pale greenish yellow in the ‘Kadota’ and ‘Genoa’ figs to white with a purple blush in ‘Conadria’ figs. Cultivated trees produce large numbers of fruits, which can become a nuisance when they ripen and drop, but those growing wild in canyons and riparian (riverside) forests around California’s Central Valley usually produce only a few greenish yellow fruits that ripen in late summer or fall.
Moraceae. Tree up to 30 ft (10
m) tall, winter-deciduous, leaves dropping in mid- to late autumn and emerging
again in early spring (March-April) in California. Leaves with petioles <4in
(<10 cm) long, blades with 3-5 palmate lobes usually halfway to the midrib,
blades broadly ovate to round in overall outline, 2-8 in (5-20 cm) wide and 2-10
in (5-25 cm) long, bright green to dark green, scabrous on upper surface, hairy
on lower surface. Plant is gynodioecious (two sexual forms), one, the
caprifig, with staminate (male) flowers and short styled pistillate (female) flowers;
the other, the fig, with only long-styled pistillate flowers. Both forms have
a complex inflorescence called a synconium. Clusters of flowers are
enclosed inside the pear-shaped synconium, which has a small, scale-covered
opening (ostiole) at its distal end. Flowers visible only if the synconium is cut
open, and are unisexual, small, and more or less radial with 4 sepals and no
petals, male flowers with 4 stamens, female flowers with superior ovary and
simple style. Synconium develops into a multiple fruit, consisting of fleshy
receptacle surrounding the drupelets that form from each pistillate flower. Synconium 1.5-3 in (4-8 cm) long, color dependent on variety (on plants outside cultivation generally bright green, turning pale green to pale yellow as they
|WHERE WOULD I FIND IT?||
Edible figs invade and dominate riparian forests, streamside habitats, levees, and canal banks in and around California’s Central Valley, surrounding foothills, the south coast, and the Channel Islands (Hickman 1993). They are also widely cultivated for fruit and ornament in areas below 2,500 feet (800 m) elevation. California is one of the world’s largest producers of fig fruits (Ferguson et al. 1990).
Edible fig is most likely to escape where soils stay moist throughout the summer. It has invaded many nature preserves and parks in California. Plants form dense thickets covering roughly twenty-five acres along a seven-mile-long section of Dye Creek at the Dye Creek Preserve northeast of Chico and have begun to invade the riparian forest at Woodson Bridge State Park along the Sacramento River to the west. Several rapidly expanding fig thickets were found in the most pristine valley oak riparian forest on the Cosumnes River Preserve south of Sacramento. These thickets were repeatedly cut and the stumps treated with herbicide, but they were difficult to eliminate. Edible figs have also invaded parts of the riparian forest in Caswell State Park near Stockton. They are found on the Santa Cruz Island Preserve in disturbed sites, and scattered along coastal flats and in coastal scrub (Junak et al. 1995).
|WHERE DID IT COME FROM AND HOW IS IT SPREAD?||
Edible fig is probably native to the fertile region of southern Arabia (Ferguson et al. 1990). It was probably first domesticated outside its native region, in Mesopotamia, in the valley of the Tigris and Euphrates rivers, in what is today Iraq. It was among the earliest known fruits to be cultivated, with records dating back to the Sumerian era, roughly 4,900 years ago (Ferguson et al. 1990). The area where figs were cultivated gradually grew to encompass all nations of southwestern Asia and the Mediterranean Basin. Edible fig was first introduced to the New World in the West Indies by Spanish and Portuguese missionaries in the 1520s and then to what is now the East Coast of the United States in 1575 (Ferguson et al. 1990). Edible fig trees were introduced to California by Spanish missionaries beginning in 1769; hence this variety is known as ‘Mission’ or ‘Franciscan’ fig. Many other varieties were introduced to California for food and ornamental plantings after 1850. Commercial production of figs was hampered until the fig wasp, Blastophaga psenes , was successfully introduced to the state in 1899 (Ferguson et al. 1990). Currently, California ranks third in the world in fig production, behind Turkey and Greece, although figs rank only twenty-second in value and eighteenth in acreage among crops produced in California (Michailides et al. 1996).
It is not clear how edible fig spreads into preserves and other wild areas. It grows quickly and can spread vegetatively by root sprouts, soon forming dense thickets that exclude most other plants. Limbs that have been cut or broken and fallen to the ground can take root, and it is thought that branches broken off during storms or floods may wash up and root at downstream sites. Many birds eat the fruits and may spread the seeds. Hujik (pers. comm.) reports that deer also feed on the fruits. Seeds germinate only if they are removed from the fleshy synconium during passage through an animal’s gut or by mechanical means such as heavy rainfall (Lisci and Pacini 1994).
|WHAT PROBLEMS DOES IT CAUSE?||
If not controlled, edible fig trees could crowd out native trees and understory shrubs characteristic of California’s riparian forests. Riparian forests are already rare in California, especially in the Central Valley, where over 95 percent have been converted to cropland, pasture, or developed areas in the past 150 years. No published or unpublished reports are available with quantitative information on the impacts of edible figs invading natural vegetation in California or elsewhere.
The leaves of edible fig contain at least two furocoumarin compounds that are activated on exposure to a certain waveband of light and can then cause a skin rash in humans (Damjanic and Akacic 1974, Evans and Schmidt 1980). The activated furocoumarins are primary irritants, meaning they chemically or mechanically irritate the skin rather than causing an allergic response. The mode of action of these compounds is not known, but they may photobind to DNA and/or ribosomal RNA in epidermal cells following exposure to ultraviolet light in the 320-370 nm waveband (Evans and Schmidt 1980).
|HOW DOES IT GROW AND REPRODUCE?||
Most edible fig fruits with viable seeds are produced in late summer and in autumn. Studies in Europe indicated that, once freed from the fleshy synconium, edible fig seeds may germinate in autumn or in spring, depending on climatic conditions (Lisci and Pacinia 1994), and the same presumably is true in California. Seeds germinate at temperatures between 50 and 85 degrees F (10 - 30 degrees C), but only if humidity remains high or if they are in contact with soil that is continuously wet (Lisci and Pacini 1994).
Edible fig grows quickly in soils with enough moisture and with exposure to high light levels. It is winter-deciduous, and the timing of leaf-out and leaf drop varies with the cultivar and with climatic conditions.
Edible fig reproduces by seed and by vegetative growth. Most of the world’s Ficus species depend on a species-specific agaonid wasp (family Agaonidae, Hymenoptera) for pollination. Ficus carica depends on the wasp Blastophaga psenes. The wasps are in turn dependent on F. carica because they breed only inside its fruits (Kjellberg et al. 1987). Fertilized female B. psenes wasps squeeze through the scale-covered ostiole in the end of the synconia of caprifigs and lay one egg in each of several of the short-styled female flowers. Each wasp larvae destroys a female flower as it feeds and grows. Female flowers that escape the egg-laying may each produce a single viable seed if pollinated. Adult male wasps emerge first and quickly cut into flowers containing female wasp larvae and mate with them. These female wasps emerge two to three weeks later and, as they make their way out of the synconium, they pick up pollen from the male flowers clustered near the opening. They then search for another, younger synconium and squeeze through the narrow opening to reach the flowers inside. Galil and Newman (1977) found that the opening is so small that it is likely all pollen on the body surface of the wasp is scraped off as it squeezes through. They speculate that the wasps carry pollen in cavities on their bodies (e.g., between abdominal segments) and that these pollen grains fall out and onto fig flowers when the wasp’s body swells and twists as it attempts to deposit eggs. The wasps insert their ovipositors down the style tube to deposit their eggs, but the styles of the female flowers in fig synconia are so long that they prevent the wasps from successfully depositing eggs. During their exertions, however, the wasps deposit pollen and fertilize these flowers. The undamaged, pollinated long-styled female flowers develop into tiny seeds within the synconia. Seeds from these flowers can produce both types of tree, caprifigs and figs (Beck and Lord 1988). Once a female B. psenes wasp has entered a synconium to lay eggs, it cannot leave, so these individuals are destined to die without producing offspring (Kjellberg et al. 1987).
In California caprifigs produce three crops of fruit, one each in winter, spring, and summer. If climate allows, figs may produce two crops, a small one initiated in spring and maturing in June or July and a main crop initiated between May and July and ripening between August and December (Ferguson et al. 1990). Staggering of fruit crops enables the fig wasp to survive throughout the year and ensures pollination of flowers in fig synconia. The synconia of the main crop of Smyrna varieties of edible fig, including the ‘Calimyrna’ cultivar, will abort and fail to develop if flowers are not fertilized. Synconia of common figs, including the ‘Mission,’ ‘Adriatic,’ and ‘Kadota’ cultivars, can develop fully even if the flowers are not pollinated and no viable seeds are produced (Ferguson et al. 1990).
Because the wasps can carry fungal disease spores, California fig growers often grow caprifigs apart from fig trees and distribute ripe caprifig synconia with emerging wasps around their orchards only after checking them for disease (Michailides et al. 1996). It is not known whether the edible fig trees that have invaded natural areas in California are all of one variety, nor is it known whether the individuals are caprifigs (with male and short-styled female flowers) or figs (with only long-styled female flowers).
The fleshy tissue of the synconium apparently contains inhibitors and/or creates a microenvironment with high osmotic pressure that prevent seeds from germinating (Lisci and Pacini 1994). Birds and mammals feed on and pick apart the fig fruit and then excrete or drop seeds, releasing them from this inhibition and usually distributing them as well. Seeds may also be washed free of the synconium by hard rains after they fall to the ground and split open.
|HOW CAN I GET RID OF IT?||
An efficient control method for edible fig has not yet been developed. The trees resprout vigorously after cutting and are difficult to control without herbicides.
Manual/mechanical: Edible figs are shallow-rooted in heavy, wet soils typical of riparian forests and can be pulled up fairly easily when young. They often root-sprout, however, so that what looks like one small sapling may be one of many sprouts from a large network of roots. A small or medium-sized weed wrench may help remove some of the mid-sized specimens. Repeated cutting of resprouts may eventually exhaust the root reserves of a tree or small thicket if the interval between cuttings is short enough, but this has not yet been demonstrated.
Insects and fungi: No biological control species are approved by the USDA for this species. However, figs are subject to damage from nematodes, tree borers, and rust.
At the Cosumnes River Preserve all trunks and sucker shoots in a thicket were cut six to eighteen inches above the ground and the cut stumps treated with a 100 percent solution of an amine formulation of triclopyr (sold under the names Garlon3A® and Brush-B-Gone®). This was successful, although some thickets had to be retreated at least once because there was some resprouting. The retreatments were carried out at yearly intervals, but shorter intervals (two to six months) might have improved their impact by giving the plants less time to replenish root reserves. Managers at the Cosumnes River Preserve recently have been using a hack-and-squirt method, applying 100 percent triclopyr amine formulation to the wounds, but it is too early to tell if this will be as effective as the cut-stump treatments. This method was also tried at the Dye Creek Preserve, but was not effective there.
Herbicide may be applied in an eight- to twelve-inch-wide band around the uncut trunks of trees with trunk diameters up to two or three inches and perhaps greater. This is known as basal bark application, and it has been shown to be highly effective for a variety of trees and shrubs. Other herbicides, including glyphosate (marketed under a variety of names, including Rodeo® and Roundup®) and imazapyr (as Chopper® and Arsenal®) may be at least as effective as triclopyr against edible fig, but studies of this have yet to be conducted.