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Copyright 2005, Board of Trustees, University
J. P Fort Pierce ARC Research Report RL-1973-1
3- August, 1973
GOOSEGRASS AND OTHER WEED HOSTS OF SCLEROTIUM ROLFSII
AT THE AGRICULTURAL RESEARCH CENTER, FORT PIERCE
R. M. Sonoda
Sclerotium rolfsii Sacc., incitant of "Southern Blight," can be an
important disease in tomato fields in the sandy soils of south Florida, i;
especially when tomatoes are grown on previously cropped land. It isa.....--
regular appearing and important disease in tomato plantings at the
Agricultural Research Center, Fort Pierce (ARC-FP). The fungus attacks
many crop and weed plants (1). It survives from one crop to the next
as sclerotia, compact masses of mycelia resembling mustard seeds.
Sclerotia are produced on plants infected with S. rolfsai or on plant
debris colonized by the fungus.
A survey was made in i planting of tomatoes after the crop was
harvested at the ARC-FP to determine which weeds served as hosts for the
fungus. The tomatoes were planted in the spring of 1973 in an area
approximately 150 x 400 feet. Keys used to identify weeds were those
of Long and Lakela (5) and Small (6). Weeds present in greatest number
were goosegrass (Eleusine indica (L). Gaertn.), Cyperus spp, and common
purslane (Portulaca oleracea L.). Weeds present in moderate to light
amounts were carpetweed (Mollugo verticillata L.), American burnweed
(Erechtites hieracifolia (L.) Raf), yerba-de-tago (Eclipta alba L.),
Amaranthus viridis L., pink purslane (Portulaca pilosa L.), Oldenlandia
corymbosa (L.) Lam., Vigna repens (L.) Kuntze, black night shade (Solanum
nigrum L.), cudweed (Gnaphalium sp.), white clover (Trifolium repens L.)
and annual sowthistle (Sonchus oleraceous L.).
The only weed consistently infected with S. rolfsii was goosegrass.
In counts made of five lots of 100 goosegrass plants in different areas
of the field, from 5 to 155 were infected with the fungus. Only two
common purslane (about 0.01%), two American burnweed (about 1%), one white
clover (about 1%), one Cyperus compressus L. (about 0.01o), and one C.
microdontus Torr. (about 0.1O) plants were attacked by the fungus. The
fungus was observed on the only Pangolagrass (Digitaria decumbens Stent.)
plant found in the field. Pangolagrass, a common pasture grass in south
Florida, is used in rotation with tomato (3). Rotation with this grass
has eliminated root-knot nematodes (7) and reduced the incidence of soil-
rot of tomatoes incited by Rhizoctonia solani (4). The rotation does not
appear to reduce the incidence of southern blight (N. C. Hayslip, personal
l/ Assistant Plant Pathologist, University of Florida Institute of Food
and Agricultural Sciences, Agri.-'slure~l. I te?1 rrb -nter-_, ~r.k-J ..a-
communication). This to the author's knowledge is the first report of
S. rolfsii on E. indica, C. compressus, C. microdontus, and D. decumbens.
S. rolfsii is aided in attacking host plants by the presence of dead
and dying plant parts (2). Suitable substrate for ingress of the pathogen
was provided by: a) .Injury or death of goosegrass leaves resulting from
a nutrient deficiency in areas away from sources of fertilizer; b) attack
by a stem borer; and c) burial of areas of a plant following shifting of
soil during rains. Additional plant debris was provided by dying tomato
plants attacked by S. rolfsii. Although infected goosegrass plants were
present between rows and in roadways, more diseased plants were found
near dying tomato plants. In some cases vigorously growing goosegrass
plants near sources of nutrients, not buried by sand, not attacked by
the borer and in the absence of tomato vine debris were infected.
A large number of sclerotia were produced on infected goosegrass
and other infected weeds. These sclerotia serve as inoculum for disease
development in a subsequent crop. Good weed control is thus an important
prerequisite to keeping inoculum for this disease at a minimum.
1. Aycock, R. 1966. Stem rot and other diseases caused by Sclerotium
rolfsii. North Carolina Ag. Exp. Sta. Tech. Bul. 174 202 pp.
2. Boyle, L. W. 196. The ecology of Sclerotium rolfsii with emphasis
on the role of saprophytic media. Phytopathology 51: 117-119.
3. Hayslip, N.C., E. M. Hodges, D. W. Jones, and A. E. Kretschmer, Jr.
1964. Tomato and Pangolagrass rotation for sandy soils of south Florida.
Fla. Ag. Exp. Sta. Circ. S-153.
4. Hayslip, N.C. and R. E. Stall. 1959. Severity of tomato soil-rot
caused by Rhizoctonia solani as influenced by former pasture crops.
Plant Dis. Reptr. 43: -T81820.
5. Long, R. W. and 0. Lakela, 1971. A flora of tropical Florida.
University of Miami Press Coral Gables, Florida. 962 pp.
6. Small, J. K. 1933?- Manual of the southeastern flora. University of
North Carolina Press Chapel Hill, N. C. 1554 pp.
7. Winchester, J. A. and N. C. Hayslip. 1960. The effect of land
management practices on the root knot nematode, Meloidogyne incognita
acrita, in south Florida. Proc. Fla. State IIort. Soc. 73: 100-104.