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Copyright 2005, Board of Trustees, University
imeograped Report No. SUB67-2
Mimeographed Report No. SUB67-2
University of Florida
SUB-TROPICAL EXPERIMENT STATION
CONTROL OF VERTICILLIUM WILT IN
ROCKDALE SOIL IN DADE COUNTY, FLORIDA
C. W. Averre, III, and J. W. Strobel
iF.A.S. U'v. of Floda
Verticillium wilt was first reported in Dade County in tomatoes by Conover (1959).
Strobel (1960 and 1963) reported the disease in numerous weed hosts, purslane
(Portulaca oleracea L.) pennyroyal (Hedeoma pulegioides Pers.) and nightshade
(Solanum gracile Link.) and vegetable crops okra (Hibiscus esculentus L.), straw-
berry (Fragaria chiloensis Duchesne var. ananassa Bailey), various cucurbits, and
others less commonly grown. The disease is most evident during cool weather in fall,
winter, and spring. Susceptible crops have been grown successfully on infested land
during the summer without any apparent ill effects.
The disease may be disastrous, or very slight, depending on the crop and on the time
and extensivness of infection in the field. Okra, 'Clemson Spineless', and straw-
berry, 'Florida 90', are so susceptible that early and extensive infection will
likely result in major losses. Tomato, var. 'Homestead -24', is more tolerant than
the above crops if infection does not start in the young seedling. Even so, reduced
yields can be expected. Trellis-grown tomatoes (vars. Manalucie, Manapal and
Floradel) are more susceptible than ground types. Although cucurbits are suscepti-
ble, the disease is seldom a problem in commercial plantings.
The disease is caused by the fungus, Verticillium albo-atrum Reinke & Berth., which
lives in the soil between crops and can probably survive several years without a
living host plant. Weeds extend the life of the fungus in the soil since many are
susceptible and some may be symptomless carriers. The fungus is spread from one
field to another on contaminated farm equipment, on infected transplants and may
also be spread by aerial spores.
Planting of resistant varieties is the most satisfactory solution to the disease
problem. Commercially acceptable verticillium wilt-resistant strawberry and both
ground and trellis type tomatoes are being developed at this Station and should be
available in the near future.
Once a crop is diseased nothing can be done to control wilt, except to maintain
optimum soil moisture, soil fertility, and control of other diseases and pests.
Fields which do not have a history of the disease should be selected for susceptible
crops to be grown during the cool season. The same is true for other soil-borne
diseases such as root-knot and root-rots. The effect on crops of various diseases
is generally additive. Fields should be maintained in weed-free fallow previous
to planting for a period of six months to minimize damping-off and root rot and to
insure reduction in root-knot nematode and the thorough decomposition of previous
crop trash (Winchester and Averre, 1966).
Chemical treatment of infested Dade County Rockdale soil with chloropicrin and
Vorlex soil fumigants is effective in reducing the incidence of the disease (Averre
and Strobel, 1966); for each treatment the following directions should be followed:
(1) The soil must be free of plant trash, i.e. the previous crop and weeds
must be thoroughly decomposed.
(2) The soil moisture must be high, near field capacity, and should be main-
tained in this condition one week before treatments are applied and for
several days after application.
(3) The fumigants should be injected at least four inches below the soil
surface, and immediately afterwards, the treated area should be dragged,
rolled, and covered with plastic mulch. If plastic mulch is not used,
.25 to .50 inches of water should be applied to provide a "water seal".
(4) The treated land can be safely planted under most conditions 12 days after
application, and sometimes within a shorter period depending on soil tem-
perature and moisture.
(5) If the fumigants are applied in bands, instead of treating the entire
field, care should be taken to avoid dragging the untreated soil into the
treated area. Plastic mulch culture is especially effective in preventing
reinfestation of treated soil. (Averre et al., 1966).
In one test without the use of plastic mulch the percent of okra plants infected
was reduced from 48 to 24 and 14 with the use of Vorlex at the rate of 25 and 50
gallons per broadcast acre (gpa). In another test in which plastic mulch was used
the same treatments reduced the percent of plants infected from 33 to 11 and 5
respectively. Chloropicrin at the 25 and 50 gpa rate reduced the incidence to 4
and 2%. These materials are excellent soil fungicides, nematodices and insecticides
and herbicides (Averre et al. 1965).
The amount of material used per acre would of course depend on the rate selected
and type of application. For example, if the injection equipment is calibrated to
deliver 35 gpa into beds 4 ft wide spaced 7 ft apart the amount of fumigant needed
for a field acre would be 20 gal. The chisels should be spaced 8 inches apart and
must not become clogged.
If the treated area is to be planted soon after treatment, the fertilizer should
contain half of the N in the form of N03. This is necessary -- particularly with
okra -- because fumigants may kill nitrate forming bacteria.
Work is currently in progress to determine the effect of disease control on yields
of tomato and strawberry and to get better estimates of proper rates. In the mean-
time rates of 35-50 gpa of either Vorlex or Chloropicrin are recommended for those
who need a control for soil borne diseases. Both Vorlex and Chloropicrin have been
cleared for use on vegetable crops.
These soil fumigants are corrosive and cause painful burns to skin and eyes; they
are extremely penetrating to clothing and leather. Goggles and gloves of poly-
ethylene or Teflon should be worn at all times. In the event of accidental
contact with the skin the fumigant should be removed immediately with dry rags or
with copious amounts of isopropyl alcohol followed by soap and water rinses; if
clothing becomes exposed remove them with haste; if the fumigant is splashed in the
eyes, wash them with large amounts of water or water containing 5% sodium bicarbo-
nate; continue treatment with ophthalmic hydrocortisone ointment.
It is wise to handle fumigants in the open air, keep to the windward, wear protective
clothing, have first-aid items on hand, and be thoroughly familiar with the manu-
facturer's label. Do not discard unused materials or cans in canals or other bodies
of water where they become potential hazards to both man and wildlife. Bury unused
fumigants and destroy empty containers prior to placing them in a county or city
Averre, C. W., III, and J. W. Strobel. 1966. Evaluation of chemicals for control
of Verticillium wilt in a subtropical calcareous soil. (Abstr.) Phytopathology
Averre, C. W., III, J. W. Strobel, and J. D. Dalton. 1966. New methods solve "old
land" problems. Sunshine State Agricultural Research Report 11(3): 120-124,
Conover, R. A. 1959. Verticillium wilt of tomato in Dade County, Florida.
Proc. Fla. State Hort. Soc. 72: 199-201.
Strobel, J. W. 1960. Studies of the Verticillium wilt disease in south Florida.
Proc. Fla. State Hort. Soc. 73: 168-172.
Strobel, J. W. 1963. Verticillium wilt of strawberry in Dade County, Florida.
Proc. Fla. State Hort. Soc. 76: 111-114.
Winchester, J. A., and C. W. Averre, III. 1966. Soil management for nematode
control in calcareous soils. Proc. Fla. Soil and Crop Soc. (In press).
Averre, C. W., III, J. A. Winchester, and J. W. Strobel. Soil treatments for
tomatoes growing under plastic mulch in calcareous soils. Proc. Florida
State Horticultural Soc. 78: 120-124.