Biology and Management of Long-Stalked Phyllanthus in Ornamental Crop Production

Species Description

Class: Dicotyledonous plant

Family: Euphorbiaceae (Phyllanthaceae)

Other Common Names: Mascarene Island leaf-flower, long-stalked leaf-flower, phyllanthus

Life Span: Summer annual or short-lived perennial

Habitat: Occurs in disturbed areas, greenhouses, turf areas, landscape beds, and nursery containers. It is found most often in sunny locations that are irrigated or remain moist. Once established, long-stalked phyllanthus can become more drought tolerant and survive in drier locations.

Distribution: Long-stalked phyllanthus is native to tropical regions in Africa and Asia but has naturalized throughout Hawaii, the southeastern U.S., and parts of Europe (Crisafulli, Picone, and Zaccone 2011; USDA NRCS 2015).

Growth Habit: Erect (upright) growing up to 2 feet tall but typically seen at 3 to 12 inches in height. Long-stalked phyllanthus typically produces a single main stem that may branch toward the stem apex (top) (Figure 1).

Seedling: Cotyledons are pale green with opposite, spatulate (spatula-shaped) leaves with smooth margins. First true leaves are typically darker green. Stems are reddish to pink in color (Figure 2).

Shoot: Stems are thin, round, and reddish to brown in color. Leaves are small (1 cm), green, elliptic in shape with netted venation, and alternately arranged. The small size of the leaves make them appear as though they are compound and resemble those of legumes. Stipules are present and about 1 to 2 mm long. No milky sap is present when stems are broken.

Roots: Dense fibrous root system.

Inflorescence: Inconspicuous, star-shaped, pedicellate white flowers (approximately 2 mm long) are found in the leaf axils (Figure 3). Flowers are monecious, with male and female flowers found on the same plant.

Fruit and Seeds: Round fruits are produced on long stalks, approximately 0.5–1 cm, and covered with rounded bumps (Figure 4). Seeds are very small (1 mm) and dark to light brown or tan in color. Fruits are explosively dehiscent and expel seeds over 3 feet when ripe.

Similar Species: Phyllantus urinaria (gripeweed, leafflower, or chamberbitter) is very similar in appearance to P. tenellus (Figure 5). Both appear as small, leafy herbs with an upright growth habit and multiple thin branches concentrated toward the terminal apex with fruits/flowers hanging below the leaves. The primary difference is that P. tenellus has seed capsules on long stalks, whereas P. urinaria has sessile seed capsules that lack stalks (Wunderlin and Hansen 2003; Bryson and DeFelice 2009) (Figure 6). In addition, P. tenellus leaves are chartaceous (papery) and stems are wiry, whereas P. urinaria leaves are somewhat coriaceous (thickened) with fleshier stems. Both species thrive in the same environments and have similar biology.

Plant Biology

Long-stalked phyllanthus is a summer annual weed, but can be seen throughout the year in Florida and may occur as a short-lived perennial in southern Florida if frost does not occur. Long-stalked phyllanthus seedlings typically emerge in late spring and throughout the fall, and may begin flowering and producing seed when only a few inches tall (Neal and Derr 2005). Seedlings can develop under mature plants, but high germination rates are common if seeds are exposed to full sun (Wehtje, Gilliam, and Reeder 1992). Studies on the similar species Phyllanthus urinaria (chamberbitter) showed that warmer temperatures (77 to 95°F) and twelve hours of light resulted in germination rates of 82 percent (Wehtje, Gilliam, and Reeder 1992). Germination is inhibited by dry conditions, so these species typically are more of a problem in irrigated areas or during periods of frequent rainfall (Wehtje, Gilliam, and Reeder 1992).

Management

Physical and Cultural Control

Long-stalked phyllanthus commonly grows in the potting media of container-grown ornamentals and often through drainage holes in nursery containers or through tears in nursery fabric close to irrigation risers. It is a problem in greenhouses, propagation houses, non-crop areas, and landscapes including both turf areas and landscape beds. As long-stalked phyllanthus germination increases in moist environments, reducing irrigation can be effective, but may not be practical in container production nurseries. Group plants by water requirement and ensure irrigation systems are well-maintained and are applying irrigation uniformly. Hand pull long-stalked phyllanthus as soon as it is seen. Once established, both Phyllanthus species can be difficult to hand weed due to their extensive root systems. Due to the high light requirements needed for germination, mulching can be effective. In a study on P. urinaria germination, deep shade and mulching reduced germination to as little as 2 percent (Wehtje, Gilliam, and Reeder 1992).

Chemical Control

Preemergence

Long-stalked phyllanthus can be difficult to control. In addition to normal sanitation practices which should always be followed for any weed species (Norcini, Bolques, and Stamps 2010), preemergence herbicides containing prodiamine (Barricade®), isoxaben (Gallery®, and as a component of Snapshot®, Gemini®, and others), oryzalin (Surflan® and as a component of XL® 2G, Rout®, and others), oxadiazon (Ronstar® and as a component of Jewel™, RegalStar®, and others), oxyflurofen (Goal® and as a component of Rout®, Double O™ E-Pro, OH2®, Biathlon®, and others) and dithiopyr (Dimension®, and others) have been shown to be effective in container trials (Norcini and Aldrich 1992, 1993; Norcini, Stamps, and Aldritch 1995). However, previous studies typically have shown variable results (Norcini, Stamps, and Aldritch 1995). Other active ingredients that are effective include flumioxazin (Broadstar®, SureGuard®) and indaziflam (Marengo®). A partial list of preemergence herbicide labeled for use in and around ornamentals for control of long-stalked phyllanthus is given in Table 1. It should be noted that control can be variable with this species. Additional products are available that also may be effective.

Postemergence

Many postemergence herbicides are effective for phyllanthus control, but most have to be applied as a directed application (no contact with desirable plant foliage). Some of the effective active ingredients which can be used in and around nurseries and landscapes include glyphosate (RoundUp®), glufosinate (Finale®), diquat (Reward®), and pelargonic acid (Scythe®). Postemergent herbicides are classified as either contact or systemic. Contact herbicides (diquat or pelargonic acid) kill or injure the plant tissue that comes in contact with the herbicide but are not translocated throughout the plant and will not kill roots, so very large phyllanthus may be able to recover. Contact herbicides must be applied to fully cover the weed to provide control and are most effective on smaller weeds. Translocated herbicides (glyphosate, glufosinate) move from the contact/absorption site throughout the plant to other tissues. All postemergence herbicides are most effective on weeds that are actively growing. Ensure that you read and understand the pesticide or herbicide label in its entirety before buying or applying any product. Always consult the manufacturer's label before application and follow all precautions and directions. Anyone possessing, handling, or applying a herbicide or pesticide can be held liable for damages, losses, or consequences from not following label instructions. For more information on good herbicide practices, please see Preemergence Herbicides for Use in Ornamentals (https://edis.ifas.ufl.edu/wg058).

References

Bryson, C. T. and M. S. DeFelice. 2009. Weeds of the South. Athens, GA: University of Georgia Press.

Crisafulli, A., R. M. Picone, and S. Zaccone. 2011. "Phyllanthus tenellus (Phyllanthaceae) a new alien species naturalized to Sicily, first record for Italy." Fora. Mediteranean. 21:293–297.

Neal, J. C. 1998. Postemergence, non-selective herbicides for landscape and nurseries. Horticulture Information Leaflets 10/98 HIL-648. Raleigh, NC: NC State University.

Neal, J. C. and J. F. Derr. 2005. Weeds of Container Nurseries in the United States. Raleigh, NC: North Carolina Assoc. of Nurserymen, Inc.

Norcini, J. G., A. Bolques, and R. H. Stamps. 2010. Container Nursery Weed Control: Sanitation Practices to Prevent Weed Seed Contamination. ENH1050. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/ep319

Norcini, J. G. and J. H. Aldrich. 1992. "Preemergent control of Phyllanthus species." Proc. Florida State Hort. Soc. 105:200–202.

Norcini, J. G. and J. H. Aldrich. 1993. "Preemergent control of Phyllanthus tenellus and Phyllanthus urinaria." Proc. Florida State Hort. Soc. 106:262–264.

Norcini, J. G., R. H. Stamps, and J. H. Aldrich. 1995. "Preemergent control of long-stalked Phyllanthus (Phyllanthus tenellus) and leafflower (Phyllanthus urinaria)." Weed Technology 9 (4): 783–788.

USDA National Resources Conservation Service. 2014. "The PLANTS Database." Greensboro, NC: National Plant Data Team. http://plants.usda.gov.

Wehtje, G. R., C. H. Gilliam, and J. A. Reeder. 1992. "Germination and growth of leafflower (Phyllanthus urinaria) as affected by cultural conditions and herbicides." Weed Technology 6: 139–143.

Wunderlin, R. P. and B. F. Hansen. 2003. Guide to the Vascular Plants of Florida, second edition. Miami: University Press of Florida.