By Mark Czarnota
University of Georgia

We all have our top weeds to deal with in the garden. One that
continues to move up my list is leaf-flower. These 6- to 18-inch
annual weeds are a growing a problem in landscapes and the
container plant industry.

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.)