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CF5 University of Florida
CENTRAL FLORIDA RESEARCH AND EDUCATION CENTER
Research Report SAN 85-11 LARpi 1985
NIGHTSHADE PROBLEM IN FLORIDA1 OCT 23 1987
Walter T. Scudder Univeisity of Florida
Several species of nightshade, members of-the genus Solanum, are
weedy plants infesting crop fields in Florida. There has been much
confusion regarding the taxonomy of this group, but recent authorities
identify the predominant weedy nightshade in Florida as S. americanum
Mill., American black nightshade. According to Ogg, Rogers, and
Schilling , this is one of the four most important weedy species in
the black nightshade group. Solanum nigrum L., the true black night-
shade as originally known in Europe, is restricted primarily to the
Pacific coastal areas of the U. S. and Canada. American black night-
shade is found in southern California and the southeastern U. S.
Solanum ptycanthum Dun., eastern black nightshade, is distributed
throughout the central and northern U. S., east of the Rockies. The
fourth species, S. sarrachoides Sendt., is less common and found locally
throughout North America. A fifth species, S. nigrescens Mart. & Gal.
(Synonym: S. gracile Dunal) occurs in south Florida. It has been called
graceful nightshade. It is similar to S. americanum, but has larger
flowers with recurved sepals and petals-T21]. All of the above species
are non-thorny herbaceous annuals and have become economic problems in
cultivated crop fields.
Besides American black nightshade, several other members of the
genus Solanum occur occasionally as problem weeds in Florida. In
central and southern citrus groves, Brazilian or climbing nightshade
(S. seaforthianum Andr.) is a problem when it grows up through and over
trees forming a dense canopy. Like many other weeds, it was introduced
as an ornamental and has escaped from cultivation [9,18,21]. Two
thorny nightshade species also occur occasionally as serious pests,
principally in pastures and groves. These are horsenettle, S. carolinense
L., and soda-apple, S. capsicoides All. (Syn. S. ciliatum Lam., not S.
aculeatissimum Jacq. as given in most books and the Weed Science Society
of America Composite List of Weeds [13,21, and personal communication
from D. W. Hall, University of Florida Herbarium].)
Although the presence of most of these nightshade species in crop
production areas has been known for some time, their existence as serious
problem weeds was not apparent until recent years . Commercial pro-
duction practices and nightshade's resistance to control measures have
led to a significant increase in its importance. In surveys reported by
the Southern Weed Science Society, black nightshade was listed in 1979
among the ten most common weeds of vegetables in Florida and among the
ten most serious weeds increasing in economic importance . It also
was listed as one of the ten most troublesome weeds in soybeans in
Tennessee, and in citrus and cotton in Texas .
Invitational paper presented at the Eighth Florida Weed Science Society
meeting, Cypress Gardens, FL, March 12, 1984.
Today, American black nightshade is the leading problem weed
growing in competition with several Florida vegetable crops. It is
especially frequent in tomato, pepper, eggplant, and watermelon fields
[3,5,17]. Among field crops, it is often a problem in corn and soy-
beans. According to Keeley and Thullen , one plant can produce 1000
berries and 20 to 30 thousand seeds. Other authors [4,14] have reported
even greater seed production, up to 100 million seeds per acre.
Beside causing serious crop losses through competition for sun-
light, water, and nutrients, nightshade is a host for several plant
diseases. Orsenigo and Zitter  reported that black nightshade is a
carrier of of potato virus Y (PVY), tobacco etch virus (TEV), and
tobacco moasic virus (TMV). All three of these are serious virus
diseases of pepper and tomato. In addition, PVY is a threat to potato
A major factor in the rapid increase of nightshade in south Florida
has been its tolerance to the herbicides labeled for use in solanaceous
crops. For example, eight herbicides are registered for selective pre-
emergence weed control in tomatoes, our leading vegetable crop .
These are amiben, bensulide, DCPA, diphenamid, metribuzin, napropamide,
pebulate, and trifluralin. These same chemicals are also labeled for
weed control in one or more other solanaceous crops, including pepper,
eggplant, potato, and tobacco. Nightshade is on the list of controlled
weeds on the label of only one of these herbicides, amiben, which must
be applied directionally to the row middles of mulched beds or as
granules postemergence to well established plants . Since nightshade
is tolerant to most of these herbicides [6,16], it has survived exposure
to them, and without competition, it has thrived and increased.
Similarly, in potato and soybean production areas of north Florida,
nightshade has increased as a weed problem due to the lack of control by
such herbicides as trifluralin, other dinitroanilines, and metribuzin.
In addition to responding to reduced competition, weed populations
subject to repeated exposure to a selective herbicide may develop an
increased genetic tolerance to that herbicide [8,15]. This often leads
to increased aggressiveness and greater ability of the weed to compete
with other species, even in the absence of that herbicide. In the case
of black nightshade, this increased aggressiveness is evident when other
crops are grown in the same area.
Contact herbicides, such as paraquat and glyphosate, provide
effective control when applied early to emerged nightshade seedlings
. Beside mechanical cultivation, the use of these chemicals, with
postemergence directed or shielded applications, is presently the best
approach to the nightshade problem in most Florida crop situations. Due
to the lack of selective herbicides which are effective for nightshade
control, this weed remains a very serious problem to Florida growers.
1. Anonymous. 1984. Amiben Granular, Amiben Chloramben Herbicide,
and Amiben DS. In Union Carbide 1984 Chemical Guide, pp. 1-30.
2. Buchanan, G. A. 1971. Economic losses due to weeds. In Southern
Weed Sci. Soc. Res. Rep. 24:184-216.
3. Burgis, D. S. 1975. Tomato production as affected by two weights
of polyethylene coated and uncoated kraft paper mulch, with and
without fungicide-herbicide impregnation. Proc. Fla. State Hort.
4. Cooley, A. W., and D. T. Smith. 1972. Seed aspects of two
perennials woolyleaf bursage and silverleaf nightshade. (Abstr.)
Proc. Southern Weed Sci. Soc. 25:443.
5. Elmstrom, G. W., and S. J. Locascio. 1974. Evaluation of herbicides
for watermelon in Florida. Proc. Fla. State Hort. Soc. 87:179-184.
6. Fennimore, S. A., L. W. Mitich, and S. A. Radosivich. 1984.
Interference among bean (Phaseolus vulgaris), barnyardgrass
(Echinochloa crus-galli), and black nightshade (Solanum nigrum).
Weed Sci. 32:336-342.
7. Keeley, P. E., and R. J. Thullen.
on the growth of black nightshade
of planting date
H. M., and J. Gressel. 1982.
John Wiley & Sons. New York.
Herbicide resistance in
9. Long, R. W., and Lakela, Olga. 1971. A flora of
Univ. of Miami Press, Coral Gables, FL. 962 pp.
10. Ogg, A. G., Jr., B. S. Rogers, and E. E. Schilling. 1981.
Characterization of black nightshade (Solanum nigrum) and related
species in the United States. Weed Sci. 29:27-32.
11. Orsenigo, J. R., and T. A. Zitter.
in south Florida as related to weed
Hort. Soc. 84:168-171.
1971. Vegetable virus problems
science. Proc. Fla. State
12. Palmer, R. D.
Weed Sci. Soc.
1979. Weed survey Southern states.
Res. Rep. 32:111-136.
13. Patterson, D. T. (Chm.). 1984. Composite list of weeds
Standardized Plant Names Subcommittee, Weed Sci. Soc. of
32 (Supp. 2). 137 pp.
14. Quackenbush, L. S., and R. N. Andersen. 1984. Effect of soybean
(Glycine max) interference on eastern black nightshade (Solanum
ptycanthum). Weed Sci. 32:638-645.
15. Ryan, F. G. 1970. Resistence of common groundsel to simazine
and atrazine. Weed Sci. 18:614-615.
16. Scrotch, W. A. 1979. Weeds in horticultural crops.
Weed Sci. Soc. Res. Rep. 32:72-82.
17. Scudder, W. T. 1970. Weed problem changes affecting central
Florida vegetable production. Fla. State Hort. Soc. 83:138-141.
18. Simanton, W. A., and J. R.
in Florida citrus groves.
19. Stall, W. M. 1983. Weed c
production in Florida Vec
Ext. Serv. Circ. 196 H. 8
20. Tucker, D. P.
King. 1956. Weed control problems
Proc. Soil & Crop Sci. Soc. Fla. 16:
controll guide for commercial vegetable
jetable herbicide tables. Fla. Coop.
H., and R. L. Phillips. 1975. Glyphosate: a
herbicide for citrus. Proc. Fla. State Hort. Soc.
21. Wunderlin, R. P. 1982. Guide to the vascular plants of central
Florida. Univ. Presses of Florida, Gainesville, FL. 472 pp.