6- 6/f AGRICULTURAL RESEARCH CENTER
jOL Hastings, Florida .- I S'
HASTINGS ARC RESEARCH REPORT PR79-2 November 5, 1979
Jrk"I 14 e1980
CONTROL OF POTATO CORKY RINGSPOT DISEASE I N ORTEAST LORIDA, .;
D. P. Weingartner
Introduction Corky ringspot disease (CRS) of Irish potatoes is caused by tobacco
rattle virus (TRV). The virus is transmitted to potato tubers by stubby root nema-
todes (Trichodorus and Paratrichodorus spp.). Approximately 5-7,000 acres of north-
east Florida (NEF) potato fields have some level of infestation with CRS. In order
for the disease to occur, both the virus and nematode must be present in the soil.
Stubby root nematodes have been found In over 50% NEF potato fields. Fortunately,
TRV is not found in all of those fields with stubby root nematodes. The disease was
first discovered in NEF in 1946. Several fields known to be infested with CRS in
the early 1950's remain infested today. The disease is most likely spread from
field to field in soil contaminated with viruliferous stubby root nematodes. The
origin of the disease in NEF and its rate of spread in the area are not known.
Control (i) Resistance Several potato cultivars are resistant to CRS. Some of
these are Superior, Pungo, and BelRus. Atlantic also has a high level of tolerance,
however, shows moderate levels of internal browning if sufficient numbers of viruli-
ferous nematodes are present. Superior, Pungo, and Atlantic are highly susceptible
to bacterial wilt and tuber brown rot caused by Pseudomonas solanacearum. Use of
these cultivars should be avoided in fields with a past histroy of brown rot. (ii)
Chemical Effective control of CRS in NEF has been achieved with carbamate type
nematicides such as aldicarb (Temik) and carbofuran (Furadan). Soil fumigants such
as the dichloropropenes (Telone and DD), ethylene dibromide (W-85 and Soil Brom) and
organo phosphates (Nemacur) have failed to control CRS in NEF. This poses an inter-
esting question because soil fumigants have effectively controlled the disease in
every other country or state where this practice has been attempted (i.e. England,
Scotland, Germany, Netherlands, Colorado, Washington, and Idaho).
The data summarized in Tables 1 and 2 are typical for NEF with one exception. As
has been observed in previous seasons, the soil fumigants (Soil Brom and Telone II)
failed to control CRS; whereas, Temik used either alone or in combination with the
fumigants provided outstanding control. These observations agree with data from 35-
40 large scale field experiments performed during 1970-79. The exception in Table 1
was the failure of Furadan to control CRS. Incidence of the disease has been re-
duced following treatment with Furadan during most years, however, effectiveness of
the chemical has been erratic during the past three seasons.
Reasons for failure of soil fumigants to control CRS in NEF Since 1973 detailed
studies have been performed to determine why soil fumigation does not control CRS in
NEF. The results of this research are summarized below.
Mr. R. E. Harrison, a graduate student working at Hastings and Gainesville under the
direction of Dr. G. C. Smart, Jr. during 1973-75, demonstrated that: (I) stubby root
nematodes in NEF occupy the entire soil profile down to the water table; (ii) the
nematodes are capable of moving both vertically and horizontally in NEF soils; and
(iii) the stubby root nematodes used in his experiments (T. christiet and T. proximus)
do not multiply on potatoes.
Since 1975 additional work at Hastings has shown: (i) Fumigation effectively kills
stubby root nematodes in a zone 4-16 inches from the soil surface; (ii) Fumigation
fails to effectively reduce population densities deeper than 16 Inches from the soil
surface; (iii) The surviving nematodes from the deeper soil move within 45 days after
planting into the zone in which the fumigant was most effective; (iv) Temik and Temik
+ a soil fumigant also effectively reduce the population density of stubby root nema-
todes in a zone 4-16 inches below the soil surface; (v) Following use of Temik or
Temik + a soil fumigant, the movement of the nematodes from deeper soil is substan-
tially reduced; (vi) Substantial development of CRS occurs during the first 55 days
after planting; and (vii) Soil fumigation fails to control CRS in NEF because stubby
root nematodes move from deeper soil into fumigated soil after the fumigant has
dissipated. Temik apparently remains active during this period and reduces nematode
movement and subsequent transmission of TRV.
Table 1. Yields and percent corky ringspot disease (CRS). 1979 Nematicide
Efficacy Experiment. ARC Hastings, Florida.I/
Nematicide Rate/acre US Size A % tubers
Treatment in-the-row cwt/acre with CRS2/
Soil Brom 853/ 1.8 gal 269a 23.5b
Soil Brom 85 + Temik 15G 1.8 gal + 20 lb 258ab 1.5a
Soil Brom 85 + Furadan 10G 1.8 gal + 20 lb 246a-c 22.5b
Temik 15G 20 lb 254a-c 1.5a
Furadan 10G 30 lb 212cd 17.0ab
Telone II 6 gal 242a-c 20.5b
Telone II + Temik 15G 6 gal + 20 lb 255a-c O.Oa
Control -176d 18.5b
Values followed by the same letter do not vary
via Duncan's multiple range test.
2 Percent CRS determined in random 15 tuber samples from each plot.
2/ Soil Brom 85 is ethylene dibromide.
Table 2. Effects of nematicides on yields and percent corky ringspot
disease (CRS) during 1977-1979 in Bed 5 New Land. ARC Hastings, FL.1/
Nematicide Yield US Size A
Treatment Rate/acre tubers (cwt/acre)-/ Percent CRS3
1977 1979 1977 1978 1979
Temik 15G (I) 20 lb. 215a 254ab 0.4c 2.4a 3.4a
Telone II (II) 6.0 gal. 188ab 266a 17.6b 57.6c 40.3b
I + II 250a 249a-c 1.lc 0.8a 1.4a
Control 141b 218c 10.8a 28.5b 27.2b
1/ Values followed by the same letter
via Duncan's multiple range test.
do not vary significantly (P=.05)
_ No yield data taken in 1978 because stands were erratic due to severe
seed piece decay following flooding rains.
2/ Percent CRS determined by examining 30 randomly sampled tubers from
each plot and observing presence or absence of CRS.