Everglades Station Mimeo Report 59-15
Pasture Weed Control /
J. R. Orsenigo ';: ..
Weed control is an integral part of pasture management' r f a ae
climatic conditions with good growth and stand of forage plants a te
grazing load many noxious or undesirable plants are controlled by for' ecompeti-
tion plus an occasional supplemental mowing. The winter of 1957-58 was an
extreme example of conditions under which weeds can be released to grow and
dominate pasture herbage. While some weeds may provide maintenance pasturage,
undesirable bushy, noxious or poisonous weeds may become established, i.e.,
butterweedd" (Senecio glabellus) was especially noticeable in the spring of
1958. Recovery or re-establishment of pasturage following heavy grazing or
severe climatic conditions is retarded by encroached weeds.
The national annual loss from weeds and brush in grazing lands has been
estimated at $500,000,000.00; this estimate reflects heavily upon extensive
grazing areas which are less favorably situated than the Everglades. Losses
in forage and animal production attributable to weeds in the Everglades area
have not been evaluated critically, even for butterweedd" poisoning.
Two'tools" are available to help control pasture weed situations:
mechanical and chemical. Mowing is non-selective and may reduce forage slightly
and temporarily. Herbicides may be more expensive than mowing and require dis-
crimination when used in vegetable-growing areas. But, weed killing chemicals
offer ready, selective control (or eradication) of many weeds for long periods.
A recent out-of-statel/ report has emphasized certain advantages from
chemical weed control in pastures: a.) chemicals were more effective than
mowing in control of annual and perennial weeds; b.) desirable grass density
increased where weeds were controlled; c.) increased forage consumption followed
chemical weed control; and, d.) greater aftermath was available where chemicals
The potential advantages and economic role of effective herbicides in the
Everglades area will be evaluated in a recently initiated pasture weed control
program at this Stationg/. The following general procedure will be used:
1. Evaluate new and established herbicides under greenhouse and/or small
field-plot conditions for effect on specific weeds and pasture grasses;
2. Evaluate the selected, effective chemicals tolerated by grasses in
intermediate field plots under pasture management (including mowing); and,
3. Test the final selections in large-block pasture management trials.
1. Klingman, D. L. and M. K. McCarty. 1958. Interrelations of methods of weed
weed control and pasture management at Lincoln, Nebr., 1949-55. USDA Tech.
2. Agronomy, Animal Husbandry and Horticulture sections.
A specific weed being studied currently.~ is butterweedd", Senecio
glabellus Pior. (S. lobatus Pers.).which contains an alkaloid toxic to cattle.
Butterweed is a winter-annual and- seed germination and plant growth occur locally
when compet-iion-with pasturage is easiest. (In preliminary trials at this
je~btion, germination and early growth were best under cold and wet soil condi-
tions.) The principal alkaloid in this species, senecionine, is reported at such
low levels (less than 0.1%) that, theoretically, considerable plant material
would have to be consumed to cause cattle deaths. However, local observations
are that relatively small amounts of ingested butterweed are toxic. In other
poisonous species of Senecio the rate of consuming the weed appears to affect
acute toxicity. The cumulative toxic action of Senecio-type alkaloids ant the
difficulty of detecting animals with sub-lethal doses are important factors in
evaluating this problem.
Senecio-poisoning symptoms in cattle include aimless walking and stagger-
ing in the early stages. Later, poor and roughened coat condition may develop.
Post-mortem symptoms usually include distended gall bladder; firm, congested
liver; and edema of visceral peritoneum.. By the time outward symptoms appear
liver damage is usually too extensive to permit recovery. Antidotal treatment
apparently is neither available nor applicable. Animals with high, but sub-
lethal, doses do not appear to regain full feed and "thriftiness".
Samples of Senecio glabellus have been collected locally at several
growth stages for alkaloid-level assay to determine the stages which present
the greatest hazards in cattle production-/.
Currently, 20 herbicides are in primary evaluation trials to select
chemicals which will selectively control butterweed at several growth stages.
The response of pasture plants and other weeds to these treatments is being noted.
Better than 85 percent control was obtained by MCP, 2,4-D, 2,4,5-T, or
(2,4-D 4 2,4,5-T) in three weeks time after overall spray application to Senecio
glabellus in full-bud and pre-flowering condition. A rate of 1.5 pounds per acre
(acid equiv.) of any of the above chemicals was sufficient to obtain the degree
of control indicated. The applied cost of these treatments would be in the range
of $1.50 to 3.00 per acre depending upon the specific herbicide used. The added
control of other weeds, as well as butterweed, with 2,4,5-T (and its mixture with
2,4-D) should effectively compensate for the higher cost of this herbicide.
Future trials will evaluate new and old, granulur and liquid herbicides
applied prior to and during the weed establishment. The aim of the program is
to develop economical herbicidal treatments: tolerated by pasture crops, effec-
tive against many pasture weeds, and non-hazardous in vegetable areas.
3. The cooperative assistance of Dr. H. L. Chapman, Jr., Dr. V. E. Green, Jr.,
and Mr. R. W. Kidder is acknowledged.
4, Cooperatively with Dr. W. M. Lauter, College of Pharmacy, University of
Florida, who is conducting the alkaloid determinations.
CHEMICAL CONTROL SUGGESTIONS FOR COMMON EROADLEAF PASTURE WEEDS
A. 2,4-D, 1 1 Ib/A acid equiv. (amine salt formulation*)
Stickerweed, Amaranthus spinosus**
Butterweed, Senecio glabellus (S. lobatus)
B. 2,4-D 4 2,4,5-T, 1 1i lb/A acid equiv. (amine salt formulation*)
(Mixture at 1 to 1 ratio)
Milkweed, Asclepias sp.**
Jerusalem oak, wormseed, stinkweed, Chenopodium sp.**
Butterweed, Senecio glabellus
Teaweed, Sida sp.**
C. Method of application
1. Low spraying pressure, 20-30 psi
2. Low spray volume, 10-30 gpa
3. Low-mounted brush broom, adjusted so that flat fan nozzle tip patterns
overlap at top of weed growth.
D. Conditions of application
1. Physical drift hazards of 2,4-D and 2,4,5-T herbicides (and possible
vapor or post-volatilization movement) are minimized by using the
above application methods and the amine salt formulations.
2. As a general "rule-of-thumb", 2,4-D type herbicides should not be
applied less than one-half mile from sensitive crops if wind is more
than a light breeze (1-3 mph) or is toward susceptible crops.
E. Florida Agricultural Experiment Station Bulletin 532, "2,4-D for post-
emergence weed control in the Everglades" by Charles C. Seale, John W.
Randolph, and Victor L. Guzman is suggested as a reference for further
New low volatile formulations are usually slightly more effective in
controlling these weeds than the salt forms.
** If weed growth is old, woody, or very dense it is desirable to mow tops off
and apply herbicides to young regrowth.