f HUME LIBRARY


JUL 11 1972

' ) NUTSEDGE IN FLORIDA
.FAS. Univ. of Florida
by

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









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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








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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

gardens.

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.