By Mark Czarnota
University of Georgia
Leaf-flower is a commonly used name for many Phyllanthus species. Some people in Georgia have misnamed them "mimosa weed" because the leaves of some resemble those of mimosa. Part of the Euphorbiaceae family, Phyllanthus is a big genus, with 700 species worldwide. They're mostly annuals, although some are weak perennials.
Only a few are common in the continental United States. Mainly, they go by the names leaf-flower, Niruri, long-stalked Phyllanthus, chamber bitter and Mascarene Island leaf-flower.
Three boogers
Only three species are real problems in landscapes and nurseries: long-stalked Phyllanthus (P. tenellus), chamber bitter (P. urinaria) and Niruri (P. niruri).The name leaf-flower comes from the tiny flowers that arise from the axils (where the plants' leaves emerge). Long-stalked Phyllanthus is named for the long stems, or "stalks," on which its flowers arise from the undersides of the leaves.
Chamber bitter and Niruri can be confused with long-stalked Phyllanthus. In nursery containers and landscapes, chamber bitter is more of a problem. Niruri, much shorter at 6 to 8 inches tall, is better able to survive in the 2- to 4-inch environment of turf grasses.
A close cousin of spurge (Euphorbia species), the long-stalked Phyllanthus can be extremely hard to control in the landscape. Like spurge, it germinates in hot, dry conditions of late spring and early summer when the soil temperatures are warm.
Tough
Once it's established, Phyllanthus is extremely tolerant of drought. It can survive even the most inhospitable conditions.All Phyllanthus species can go from seed to flower in less than two weeks. And they can produce copious numbers of seeds. Each plant can release thousands.
Another characteristic that makes Phyllanthus such a problem weed is its high tolerance of dinitroaniline herbicides such as Preen, Surflan and Barricade. These pre-emergent herbicides are the backbone of weed control in the container and landscape industry. Even when these herbicides are used, Phyllanthus has the ability to germinate when other weeds can't.
One other dubious ability of Phyllanthus is its ability to spread its seed by explosive force. When the fruits of the Phyllanthus species ripen, they explode to help disperse the seed.
What to do
One of the most important cultural approaches you can use to help control Phyllanthus is to maintain a 2- to 4-inch layer of mulch. Phyllanthus seeds are small. Not many plants will survive if they have to penetrate a thick layer of mulch.Herbicides help control this plant, too. Postemergent herbicides with the active ingredient diquat (Reward), glufosinate (Finale) or glyphosate (Roundup) will do a good job of controlling Phyllanthus after it has germinated.
If you have severe infestations, consider using pre-emergent products. When trying to control Phyllanthus with pre-emergent herbicides, consider making at least two applications, in February or March and in May or June, to cover the worst Phyllanthus germination window.
Obviously, you can hand-remove small infestations, too. But be aware that Phyllanthus is prone to breaking off at the soil level.
However you do it, try to remove all Phyllanthus plants from your garden, since each plant can produce a lot of seed. Good luck.
(Mark Czarnota is a horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)
