f HUME LIBRARY
JUL 11 1972
' ) NUTSEDGE IN FLORIDA
.FAS. Univ. of Florida
James M. Stephens and Myron Sasser
Assistant Vegetable Crops Specialist Graduate Student
Agricultural Extension Service Vegetable Crops Department
University of Florida University of Florida
You could count on your fingers the number of vegetable growers in Florida who
at one time or another have not been plagued by the bothersome nutsedge. More commonly
known as nutgrass or cocograss, this persistent pest of field and garden creates all
sorts of problems, many times causing the abandonment of crop areas. Vegetable pick-
ers sometimes hesitate to thrust their hands into thick masses of the grass for fear
of snakes. In some cases the grass acts as physical impediment to cultural practices.
Rapid growing shoots grow right through potato tubers in the soil, leaving unsightly
holes similar to those caused by wireworms. Infestations of nutgrass compete heavily
for soil moisture and nutrients needed by the vegetable crop..
There are two major species of the nutsedge genus Cyperus found throughout
Florida on all types of soil from rockland to muck. These are Cyperus esculentus,
called yellow nutgrass or more commonly chufas, and Cyprus rotundus, called purple
nutgrass. Both are weed pests, but the rotundus is a more widespread problem than
the esculentus, or chufa, which is often cultivated as livestock food, especially
in North Florida.
Nutgrass has become even more infamous due to its explosive growth rate and
resistance to normal control methods. A close look at its physical characteristics
and growth responses might help us better understand this adversary and perhaps
find a weakness in its defenses.
Nutgrass gets its name from the "nuts" it produces underground. These "nuts"
are not roots but are swollen underground stems called tubers. The pale white im-
mature tubers develop into round, rough-skinned, almost black "nuts", which have
a pleasing, nutty taste in the case of esculentus and a bitter, nutty taste in
the case of the rotundas. Tubers develop on the two species in a characteristically
different manner. The chufa produces the majority of its tubers bunched together
directly beneath the plant, with a few stragglers some distance away. Although
bunched together, each "nut" is attached to a thin underground stem (rhizome) which
connects the single tuber to the growing ahodft. On the other hand, the purple nut-
grass produces its tubers in "chains"; there may be a dozen or more "nuts". in a
"chain", all connected by a thin strand of rhizome. Several of these chains of
tubers might develop and protrude from a growing shoot. On both species roots grow
out from the underground stems, primarily from the tubers and to a limited extent i;
from the connecting rhizome.
Basic known physiological characteristics of these chain-linked tubers help to
explain the behavior of purple nutgrass in the field. Since these chains of tubers
are stems, they possess the physiological phenomenon known as apical dominance.
Essentially, this means that the major point of growth is at the top end of the
stem. Only the outer-most tuber in the chain, and sometimes the one next in line,
will germinate and produce a shoot. All the other tubers below this apical tuber do
not germinate. If, however, this apical tuber is cut loose from the chain, the
next tuber in line becomes the apical tuber and grows, exhibiting its own apical
dominance over those below it in the chain. This phenomenon holds true even for
short chains in the soil separated from the shoot.
It should be easy to envision significant application of this phenomenon in
the field. Disking would tend to sever these chains at random intervals. At each
point of cut, the tuber immediately below the cut would become an apical tuber and
would germinate; thus, disking would greatly multiply the number of germinating tubers
and growing shoots. This is exactly what happens under field conditions. Deep
hoeing would also separate the tubers and produce an outbreak of nutgrass. Therefore,
gardeners might well be wise to cut nutgrass at the soil surface by shallow hoeing
to avoid breaking up the chains.
The tuber itself also possesses the phenomenon of apical dominance. Each tuber
has a number of buds scattered over its surface, but only the uppermost bud will
germinate and produce a shoot. However, if the tuber is sliced in two, as often
happens in disking or hoeing, the bud just below the cut also will grow, creating
two shoots in an area where only one grew previously. In addition, exposure of the
tuber to light, as might happen with disking, may break the apical dominance and
cause all buds to sprout.
Noting these effects of disking, one might be inclined to think that disking as
a control measure might not be advisable since it would only compound the problem.
Such a conclusion might not be entirely correct after a look at another physiological
characteristic of nutgrass involving translocation of chemicals.
2, 4-D has been studied as a control of nutgrass. It was found that 2, 4-D
would kill all those parts of the grass into which it was translocated following
application to the shoot. However, it was revealed that such a chemical would be
translocated only into the second or third tubers on a chain, leaving the remaining
tubers alive and unharmed for subsequent reinfestation. In the case of the chufa,
failure to translocate would not be a problem, since tubers are not borne in chains.
To eradicate purple nutgrass, it would appear reasonable that the chains should
be cut into units of one or two tubers each, exposed to proper germinating soil con-
ditions to produce above ground shoots, and the shoots sprayed with 2, 4-D. Ihile
workable, such a method of eradication would take time, as several diskings and
sprayings would be required before all the tubers were separated.
Under arid conditions, as in the West, some success at controlling purple nut-
grass has been obtained from surface-drying the tubers. After repeated disking to
bring them to the soil surface, tubers lost as much as 2/3 of their water content
in 2-3 days of surface drying. Such tubers were no longer viable. Unfortunately,
here in Florida out humidity is too high and rainfall to prevalent to accomplish
control in this manner.
Almost complete eradication can be accomplished by soil fumigation with
gaseous methyl bromide. Such fumigation is expensive and can be practiced only
where cost is not an important consideration, as in the case of small plots or
Some control of nutgrass here in Florida has resulted from shade produced by the
infested crop. For example, some vegetable growers have noted a great reduction of
the grass following a crop of sweetpotatoes, and almost complete extermination fol-
lowing two or three seasons of growing sweetpotatoes. Research reports show that,
at light intensity equal to about 8 percent of bright sunlight, a "nut" would
germinate but would grow weakly and would not produce additional "nuts". Thus,
"nuts" would expend themselves without proliferation. Those familiar with the
duration and nature of a growing sweetpotato vine can appreciate the amount of
shade produced. It has also been suggested that something in addition to shade,
such as a growth-inhibitor, might be a factor involved.
Since tubers buried deep within the soil remain viable for only about two
years, fallowing has been considered helpful in the control bf nutgrass. However,
it is becoming increasingly more impractical to remove land from production for
such long periods of time. Realizing the importance of time, researchers continue
to search for quick-killing chemical-herbicides. In all likelihood, it will be
through their efforts that a final solution to the problem of nutsedge, if there
is a solution, will be found.