AGRICULTURAL RESEARCH CENTER I '
SHastings, Flori a JAN 197
Hastings ARC Research Report PR77- 4 November 1977
LF.A.S. Unv. of Florida
CORKY RINGSPOT CO olorida
D. P. Weingartner, Assoc. Plant Pathologist
J. R. Shumaker, Assoc. Horticulturist
G. C. Smart, Jr., Nematologist
Introduction. Corky ringspot disease (CRS) was first reported in the
United States when it was described from the Hastings area in 1946 (1).
The disease now has been reported in Washington, Oregon, Idaho, Califor-
nia, Indiana, and Michigan. It also occurs throughout Europe where
tuber symptoms are called spring and foliage symptoms stem mottle.
Several researchers, including Walkinshaw and Larson (4) working with
diseased potatoes and soil obtained from the Hastings area, determined
that CRS is caused by tobacco rattle virus and that the virus is trans-
mitted to potatoes by stubby root (Trichodorus spp.) nematodes.
In the United States, symptoms are usually confined to the
tubers. External lesions can range from minute brown spots to large
circular lesions with concentric zones of healthy and necrotic tissue.
Internal symptoms consist of necrotic arcs usually emanating from the
external lesions. In Europe, some strains of the virus cause a mottl-
ing of potato foliage; however, in the U. S. foliage symptoms are
*usually observed only when infected tubers are planted under experimental
conditions. Foliage symptoms have never been observed in the field in
Florida. Eddins (2) determined that several potato cultivars including
Pungo, Plymouth, and Merrimack were resistant to CRS in the Hastings area.
Pungo was the most adaptable of these to Northeast Florida (NEF). Pungo,
however, has proven to be highly susceptible to bacterial wilt and brown
rot caused by Pseudomonas solanacearum; produces secondary growth unless
carefully managed and produces commercially unacceptable potato chips
when grown in other states. For these reasons, additional resistant
cultivars and other means of controlling CRS were desired.
By 1970, we anticipated that soil fumigation for nematode
control would become an integral part of potato production in NEF.
Populations of Trichodorus christiei, the principal vector of TRV in NEF,
were observed to increase rapidly, often attaining levels several times
greater than in the nontreated controls, following fumigation of soils
planted to cabbage and other crops (3). It was not known whether T.
christiei would increase on potatoes following fumigation or whether any
population increases would result in increased levels of CRS.
Research was initiated in 1970 to determine effects of soil
fumigants and nonvolatile nematicides on populations of T. christiei and
on incidence and severity of CRS. In addition, since 1972, all seedlings
in the USDA Potato Breeding Program as well as several named cultivars
have been evaluated for reaction to CRS in order to find new sources of
dA resistance. This report summarizes a portion of this research.
Methods. Soil fumigants and nonvolatile nematicides were applied using
methods previously described (5). The plot design varied with the ob-
jectives of the experiment, however, randomized block designs were usually
used in variety evaluations and split plot designs were used for most
chemical efficacy experiments. Susceptible (Sebago) and resistant (Pungo)
controls were used in all experiments.
Results and Discussion. The results and discussion are presented in a
sequence representing the chronological development of new information
concerning control of CRS in NEF. Data are presented only for those
chemicals which are registered for use in Florida.
Experiments performed during 1970-1972 in a grower's field
(Table 1) demonstrated that CRS was effectively controlled by the
nonvolatile nematicide Furadan and that the soil fumigant Telone did not
reduce the incidence of the disease. These observations were made before
chemical control of CRS was reported in the world literature. Subsequent
experiments have confirmed these data (Tables 2, 4, 5, and 6). None of
the soil fumigants tested at Hastings, including several formulations
containing chloropicrin, which are not shown in the data tables, have
controlled CRS. In several experiments, soil fumigants have increased
the incidence and severity of CRS over levels observed in the nontreated
controls. The nonvolatile nematicides Temik and Furadan, however, have
effectively controlled CRS. Mocap and Nemacur (data for Nemacur are not
shown), two additional and nonvolatile nematicides, have failed to provide
effective CRS control.
Increasing the rates of Telone, DD, and W-85 (data for DD and
W-85 are not shown) also failed to control CRS. However, preplant soil
fumigation used in combination with at-planting applications of Temik or
Furadan provided effective control of CRS. Data from rate experiments
show that 2-3 lb/acre ai of Temik and Furadan are needed for CRS control,
even when used in combination with a soil fumigant.
In 1972 and 1973 tuber harvests made over a period of time
showed that incidence of CRS can attain high levels shortly after tuberi-
zation. During 1977, however, a significant amount of infection also
occurred late in the season. Tuber lesions resulting from late season
infection in 1977 tended to be superficial and caused relatively minor
internal necrosis. During most seasons, premature harvest of the potato
crop is not a desirable method for reducing losses to CRS.
Evaluations of the disease reactions of various potato
cultivars to CRS have shown Sebago and Red La Soda to be extremely
susceptible to CRS. Pungo, Green Mountain, Hudson, Superior, Plymouth,
Merrimack, and USDA seedling B6969-2 (to be grower tested in 1978) show
high degrees of tolerance to the disease. Each of these resistant
cultivars, however, has one or more traits limiting its use in NEF.
Wauseon, Atlantic, and Penn-71, although intermediate in their suscepti-
bility, would not provide commercial control in severely affected fields.
CRS control. Apply Temik 15G or Furadan 10G at 3.0 Ib ai/acre in-the-
row alone; or at the same rates in combination with a soil fumigant such
as Telone II or DD; or plant resistant cultivars (Pungo, Superior, or
Hudson). Use of a nematicide is generally recommended in NEF for control
of other nematodes even when the variety is resistant to CRS.
Caution. Pungo and Superior are extremely susceptible to bacterial
wilt and brown rot.
Suggested for grower trial. Temik 15G or Furadan 10G at 2.0 Ib ai/acre
in combination with the recommended rate of a soil fumigant.
1. Eddins, A. H., E. A. Proctor, and Erdman West. 1946. Corky ringspot
of potatoes in Florida. Am. Pot. J. 23:330-333.
2. Eddins, A. H. 1959. Susceptibility of potato varieties and seedling
selections to corky ringspot. Am. Pot. J. 36:187-190.
3. Rhodes, H. L. 1968. Re-establishment of Trichodorus christiei
subsequent to soil fumigation in central Florida. Plant Dis. Rept.
4. Walkinshaw, C. H. and R. H. Larson. 1959. Corky ringspot, a soil-
borne virus disease. University of Wisconsin. Res. Bull. 217. 32pp.
5. Weingartner, D. P., J. R. Shumaker, D. W. Dickson, and G. C. Smart, Jr.
1973. Improving the quality of potato tubers through use of nematicides.
Soil and Crop Sci. Soc. Fla. Proc. 33:67-72.
This research was supported in part by grants and gifts from
PPG Industries, Mobil Chemical, Mobay Corporation, Dow Chemical, Great
Lakes Chemical Corporation, HEW Contract No. 223-76-2073, FMC Corporation,
Union Carbide Corporation, and Shell Development Company.
Table 1. Effects of nematicides and potato
cultivars on percent tubers affected by corky
ringspot (CRS) lesions. 1971 and 1972 corky
ringspot experiments. ARC-Hastings, Floridai/
Nematicide Rate/ Cultivar
treatment acre ebago
1971 1972 1971 1972
Furadan 10G 30 lb. 1.2 6.9 0.0 0.0
Telone 8 gal. 20.0 0.6
Control 0 40.9 17.6 0.8 0.0
-i An additional experiment was performed in
1970, however, no CRS occurred in the test
Table 2. Effect of soil fumigants and nonvolatile
nematicides on severity of corky ringspot disease
(CRS) and Trichodorus christiei populations. Nema-
ticide Efficacy Experiment, 1972, ARC-Hastings, FL.
Nematicide CRS T. cdhlitiei/
treatment Rate/acre ratingl/ 100 cm3 soil
Temik 10G 30 lb. 1.8 a 1.7 bc
Furadan 10G 30 lb. 2.3 ab 1.7 bc
Mocap 10G 20 lb. 3.8 abc 3.3 bc
DD 10 gal. 5.6 cd 15.0 a
W-85 1.4 gal. 4.6 c 10.3 abc
Telone 8 gal. 5.6 cd 10.7 abc
Vorlex 3 gal. 5.8 cd 1.7 bc
Control 7.2 d 1.8 bc
1/ Severity of CRS was rated on a
of all tubers free of CRS and 10 = surface
Values followed by the same letters do not
scale of 1-10; 1 =
of all tubers 100%
2/ The CRS x T. chhinUti correlation coefficient (P=.06) was
Table 3. Effect of harvest dates on incidence of
external and internal tuber symptoms of corky ring-
spot disease (CRS) on Sebago cultivar. Table Stock
Experiment, 1972. ARC-Hasting, Florida.
Harvest Days after Tubers with CRS
date planting symptoms/
15 May 108 14.7 a 23.7 a
22 May 116 22.8 a 21.6 a
29 May 123 11.5 a 15.5 a
STreatment means followed by the same letter are
not significantly different (=.05).
Effect of potato cultivars and different rates of Telone on
of potato tubers affected by internal CRS. Table Stock Experiment,
1972. ARC-Hastings, Florida.
Telone Red Fumigant
rate La Soda Penn-71 Sebago Wauseon average/
gal/A2/ % % % /
0 42 34 36 19 32 a
8 18 18 27 10 18 a
10 17 8 25 6 14 a
12 15 16 26 9 17 a
average 1/ 23 ab 19 b 28 a 11 c
Values followed by same letter do no
of a letter denotes nonsignificance.
t vary significantly (P=.05). Lack
2/ Fumigant applied in row using a single chisel/row.
Table 5. Summary of the incidence of CRS in Sebago potato tubers as affected by
soil fumigation, nonvolatile nematicides and combinations of these treatments in
three series of experiments performed during 1970 1977.1
TreatmentsI/ Percent tubers with internal CRS2/ of
'71 '72 '73 '74 '75 '74 '76 '77
Telone (I) 20 18 79 27 30 18 11 29.0
Temik 15G (II) 12 0 1 4.3
I + II 10 2 4.3
Furadan 10G or 4F (III) 1 7 6* 2* 1* 12* 2 4.4
III + I 8* 2* 0 7* 5 4.4
Mocap 10G (IV) 30* 10 20.0
IV + I 12* 12 12.0
Control 41 18 32 71 29 13 11 11 29.0
SAll nonvolatile nematicides were applied at 3.0 lb ai/acre in-the-row. Telone
(8.0 gal/acre in-the-row) was used in all experiments performed during 1971 -
1975. Telone II was used at 8.0 and at 6.0 gal/acre in-the-row during 1976 -
2/ Indicates liquid formulations. % CRS is % tubers with internal necrosis
except for the 1977 experiment in which % CRS is % total weight US size A
tubers with external CRS lesions.
Table 6. Percent tubers with internal corky ringspot following
use of three different rates of nonvolatile nematicides when
used in combination with Telone II. 1976 and 1977 Nematicide
Rate Experiments. ARC-Hastings, Florida.
% CRS 1
13 b 29 abc
2 a 20 bc
3 a 21 bc
10 lb 17 b 21 bc
0 a 24 bc
2 a 18 c
10 lb 18 b 54 a
7 a 40 abc
30 lb 18 b 43 abc
6 or 8 gal
19 b 40 abc
- 27 bc
1/ Values followed by the same letter within a given year
do not vary significantly (P=.05).