AGRICULTURAL RESEARCH CENTER
PO&L -- /. Hastings, Florida
Mimeo Report POL 71-12 October 1971
NEMATODE CONTROL ON POTATOES IN THE HASTINGS, FLORIDA AREA
D. P. Weingartner, Asst. Plant Pathologist
Agricultural Research Center
D. W. Dickson, Asst. Nematologist
Entomology and Nematology Dept.
Nematode damage to potatoes in the Hastings area can be broadly classified
into three categories:
1. Reductions in total production caused by nematodes feeding
on and damaging roots.
2. Direct injury or reductions in quality of tubers (eg. root
knot nematode galls).
3. Indirect injury or reductions in quality of tubers (eg. corky
ringspot caused by tobacco rattle virus which is transmitted
by stubby root nematode).
Controlling nematodes causing each type of injury may require different
approaches. The objectives of nematode control research on potatoes at
this Agricultural Research Center have been to: (1) determine which
nematodes limit potato yields and reduce tuber quality in the Hastings area;
(2) determine lowest efficacious rates of soil fumigants under Hastings'
growing conditions. During the past two growing seasons a number of ex-
periments have been performed to give information concerning these questions.
During the 1970 season, several experiments with soil fumigants were per-
formed. Soil fumigation increased yield-of potatoes, however, the increase.
was not as striking as those observed in previous years (Table 1). Quality
of tubers was improved by each material tested. Tubers from control plots
generally were misshapen and russetted in appearance, whereas treated
potatoes were shaped normally and were smooth skinned. Potato chip color
and specific gravity were essentially unaffected by nematicide treatments.
It was not determined which nematodes were the primary pests affecting
potatoes in the Hastings area.
DEC 27 1971
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Two major experiments were performed in 1971. One was performed in soil
known to contain high populations of sting and stunt nematodes and the other
in soil known to contain high populations of sting, spiral, and root-knot
nematodes. Populations of all nematodes were relatively uniform in both test
areas. Each experiment will be discussed separately.
Experiment 1. Telone (8.0 GPA), Dowfume W-85 (1.8 GPA), D-D (9.5 GPA), and
Vorlex (3.0 GPA) constituted the treatments in this experiment. All mate-
rials were applied with gravity flow equipment. Materials were injected
at a depth of 8-10 inches with a single chisel/row. All fumigants were
applied January 25-26 and potatoes (Sebago cv.) were planted February 15.
The crop was harvested and graded May 28, 1971. Initial populations of
both sting and stunt nematodes were uniform and high at the time of appli-
All materials significantly reduced populations of sting and stunt nematodes
(Table 2). Yield of US1A, and US1B tubers were significantly increased by
all treatments. Total fresh weights harvested were inversely correlated
with mid-season populations of both sting (r=T.79) and stunt (r=-.81)
nematodes. Tuber skin quality was improved significantly by all treatments.
Specific gravities of tubers harvested from treated plots were significantly
lower than those from nontreated areas. Apparently early vine senescence
which was observed in nontreated plots was reflected in tuber maturity
characteristics. Data from this experiment suggest that sting and stunt
nematodes play an active role in reducing yields of potatoes in the Hasting
Experiment 2. Sting, spiral, and root-knot nematodes occurred in extreme-
ly high numbers in this test area, whereas stunt nematodes were absent.
The experiment was designed to determine whether: (a) yields would be
affected by the nematodes present; and (b) low rates of soil fumigants
would reduce tuber galling caused by root knot nematodes.
Materials tested included: Telone (8.0 and 6.5 GPA), Dowfume W-85 (1.8 and
1.3 GPA), Terr-o-cide 15 (3.0 and 4.2 GPA), Vorlex (3.3 and 1.9 GPA). Soil
fumigants were applied on the same dates and in the same manner as described
under Experiment 1. Potatoes (Sebago cv.) were planted February 19, and
were harvested and graded May 28, 1971.
When compared to the nontreated plots, best nematode control, greatest yield
increases and greatest reductions in tuber galling were obtained with Telone
(8.0 GPA), Dowfume W-85 (1.3 and 1.8 GPA), and Terr-o-cide 15 (3.0 and 4.2
GPA). The low rates of Dowfume W-85 and Terr-o-cide 15 were essentially as
effective as the high rates. Skin quality and specific gravity were not
POL 71-12 Page 2
significantly affected by any treatment. Tuber galling was light bo
moderate even in control plots despite high populations of root knot nema-
todes at harvest. Significant inverse correlations of yield with mid-season
populations of sting (r=-.39) and spiral (r=-.39), but not with root-knot
(r=-.17) nematodes were observed.
Applications of soil fumigants during the past two growing seasons reduced
populations of plant parasitic nematodes, increased yields of potatoes, and
improved quality of tubers. Based on these observations, soil fumigation
is suggested for nematode control on potatoes grown in the Hastings area.
Additional information concerning soil fumigation on potatoes is available
in the Florida Nematode Control Guide or from the County Extension Agent.
GENERAL INFORMATION CONCERNING SOIL FUMIGATION:
1. Cover crops should be well decomposed before soil is fumigated. Cover
crops should therefore be disked under at least 4-6 weeks before fumi-
2. Soil fumigants must be applied as preplant treatments. The materials
must be applied 3-4 weeks before planting and soil should not be dis-
turbed for 7-10 days following treatment.
3. The preplant waiting period should be extended if heavy rains and/or
low temperatures occur following soil fumigation. In addition, soil
should be reworked before planting.
4. When using soil fumigants (or any other pesticide), READ THE LABEL
CAREFULLY AND EXPLICITLY FOLLOW DIRECTIONS!!
5. Remember- failure to allow soil fumigants to diffuse from soil can
result in crop injury.
POL 71-12 Page 3
Table 1. Results of 1970 soil fumigation tests performed on po.atoes.-
Total 2/ 3/
Marketable Nematodes- Increase in Net Increase"
Rate Potatoes in 100cc Crop Value in Crop Value
Treatment (GPA) (cwt/acre) Soil ($/acre) ($/acre)
D-D 6.0 139.0* 36.3** 65.40 27.40
D-D 8.0 136.1 24.1** 52.35 14.02
Telone 6.0 146.7* 30.3** 82.80 37.90
Vorlex 4.0 135.1 6.7** 50.10 2.40
Dowfume W-85 4.0 29.6** 0.0** -
Control 113.3 221.3
1/ Data are means of 4 and 29 replicates for treatments and control respec-
tively. Values varying significantly from the control at 1% and 5% are
indicated by ** and *, respectively.
2/ Populations of sting and stunt nematodes are added together to give a
single value. Soil samples collected at mid-season.
3/ Net increase in crop value = increase in crop value minus cost of material
plus added cost to harvest and market. All calculations based on $3.00/cwt
for USIA and $1.50/cwt for USlB at harvest. Cost of chemicals based on
dealer's price list March 17, 1971. Marketing and harvesting cost ($1.035/
cwt) taken from Ag. Economic Report 15 (Costs and Returns from Vegetable
Crops in Florida Season 1969-70 with comparisons).
4/ The 4.0 GPA rate of Dowfume W-85 used in this test exceeded label restric-
tions by 2.2 GPA and was phytotoxic.
POL 71-12 Page 4
Table 2. Results of 1971 experiment for control of
sting and stunt nematodes on
Sting + Stunt3/
Marketable Yield Skin- Nematodes
Rate (cwt/acre) Quality Specific Mid- At
Treatment (GPA) US1A USlB Total Rating Gravity Season Harvest
Dowfume W-85 1.8 103.3 53.4 156.7 3.5 1.065 5 4
Telone 8.0 101.7 52.0 153.7 4.2 1.064 4 25
D-D 10.0 84.7 47.2 131.9 4.0 1.062 9 61
Vorlex 3.0 80.8 46.8 127.6 4.1 1.064 10 65
Control 38.5 34.9 73.4 6.4 1.069 304 188
1/ All data are mean values of 5 replications.
All treatment values vary
significantly from control at 1% level of probability.
2/ Skin quality ratings based on 1-10 scale with 1 being smooth skinned and
10 being totally russetted and fissured tuber surface. Reductions in skin
quality were significantly correlated with mid-season populations of sting
(r=.78) and stunt (r=.67) nematodes.
3/ Nematode counts are sums of sting and spiral nematodes extracted from re-
plicated soil samples.
POL 71-12 Page 5
Table 3. Results of 1971 experiment for control of
1/ All data are mean values of 6 replications. Significant differences from control at 1%
cated by ** anC *, respectively.
and 5% are indi-
2/ Skin quality rating based on 1-10 scale with 1 being smooth skinned and 10 being totally russetted and
fissured tuber surface, respectively.
3/ Tuber gall index based on 1-10 scale with 1=0 galls and 10= tuber surface completely covered with galls.
4/ Nematode counts are sums of spiral, sting, and root knot nematodes extracted from replicated soil samples.
Nematodes found 4/
Trr.eaa tetumenL u
sting, spiral and root-knot nematodes on potatoes.'