AGRICULTURAL RESEARCH CENTER
Hastings ARC Resear
ch Report PR78-1 0
NEMATODE AND SOIL-BORNE DISEASE CONTROL.
D. P. Weingartner, Assoc. Plant Pathologis O,
J. R. Shumaker, Assoc. Horticulturist
G. C. Smart, Jr., Nematologist <
Introduction. Plant parasitic nematodes are found in most northeast Florida (NEF)
potato soils. Unfortunately nematodes usually do not exist alone in the soil.
Several pathogenic microorganisms are found in many fields in addition to the nema-
todes. In several instances, nematodes are known or believed to play an important
role in affecting the incidence and severity of disease either by serving as vectors
or by predisposing the potato plants to attack by disease organisms.
This research report summarizes recent information on important nematodes
and nematode related soil-borne diseases affecting potatoes in NEF. Additional
details on the diseases and nematodes discussed, and from the experiments on which
control suggestions are based, can be found in recent ARC Hastings Research Reports.
The nematodes. The most important nematodes affecting potatoes in the Hastings
area are the sting (Belonolaimus longicaudatus), southern root-knot (Meloidogyne
incognita), and stubby root (Trichodorus christiei) nematodes. Several other plant
i\arasitic nematodes occur in northeast Florida potato soils including the root
* lesion (Pratylenchus scribneri), ring (Criconemoides ornatus), sheath (Hemicyclio-
phora sp.), lance (Hopolaimus sp.), spiral (Hemicriconemoides and Helicotylenchus),
stunt (Tylenchorhynchus claytoni), Scutellonema bradys, and awl (Dolichodorus
heterocephalis) nematodes. In most cases little is known concerning the feeding
behavior of these nematodes on potatoes, however, they are considered of lessor
importance than sting and root-knot nematodes because the numbers found in most NEF
ootato soils are below the recognized damage threshold levels on other crops.
Sting nematode. Sting nematode is a
remaining outside of the root and can
episodes. It feeds near the root tip
Necrosis is often observed at feeding
are pruned and stubby in appearance.
abnormally russetted when populations
migratory ectoparasite which feeds while
move about from root to root between feeding
and feeding generally stops root elongation.
sites. The roots of severely affected plants
Tubers are often misshapen, scurfy, and
of sting nematodes are high.
Sting nematodes multiply readily on potatoes and cause considerable
root damage. Reductions in potato stands were associated with sting nematode
damage on potatoes during 1977. Heavy yield losses and severe reductions in tuber
quality are usually associated with sting nematodes. The threshold density (i.e.
no./volume soil at planting sufficient to cause economic crop loss) is not establish-
ed for sting nematodes on potatoes, however, is approximately 5/100 cc for other
susceptible crops. Control procedures are generally recommended in NEF whenever
JLing nematodes are found in soil samples.
Southern root-knot nematode. This nematode is a sedentary endoparasite. The
larvae penetrate and enter the roots. Once feeding is initiated, the bodies of the
females begin to swell and the nematodes become sedentary. The host tissue sur-
rounding the head of the female under goes certain changes resulting in production
of specialized feeding cells and formation of galls. Many eggs are laid and if
roots are carefully removed from the soil, amber colored masses of the eggs can be
seen adhering to the surface of the galls.
Southern root-knot nematodes multiply readily on potato. Severe root
and tuber galling is frequently observed in NEF. Galls can form on tubers within a
few days as soil temperatures rise during late May and early June. Although density
damage thresholds have not been established for root-knot nematodes on potatoes in
Florida, control is generally recommended whenever the nematode is present.
Stubby root nematode. These nematodes are migratory ectoparasites which have
similar feeding sites and cause root damage on crops other than potato much like
that associated with sting nematodes. The potato is a poor host for stubby root
nematodes and little to no multiplication occurs on the crop. The nematode is
important principally as a vector of tobacco rattle virus, which causes corky ring-
spot (see Hastings Research Report PR77-4) and it is not known whether feeding ac-
tivity in itself seriously affects root vigor and tuber quality. Control is
generally recommended if CRS is a problem in a potato field.
Miscellaneous nematodes. Little is known concerning the feeding behavior on
potatoes of the several other plant parasitic nematodes found in NEF potato soils,
particularly when they are found concomitantly. Control is usually recommended
only if fairly high (i.e. several hundered/100 cc soil) population densities occur.
Diseases associated with nematodes. Unfortunately, the soil is inhabited by
disease causing microorganisms in addition to plant parasitic nematodes. Root
injury caused by feeding activity of the nematodes can provide entry points for
soil-borne pathogens. Diseases such as Verticillium wilt, bacterial wilt, and
tuber brown rot can be more severe following nematode injury. The soil-borne
fungus Rhizoctonia is frequently found in tubers injured by nematodes. Tobacco
rattle virus is transmitted directly to potato tubers by stubby root nematodes.
No single control procedure will control all of the nematode and
nematode-related disease problems affecting potatoes in NEF. The situation is
further complicated because the different chemicals which are available vary widely
in their performance depending upon soil conditions at the time of application and
during the period when they are intended to provide control.
Early dying disease. In other potato producing sections of the U.S., this disease
is caused by Verticillium albo-atrum. The disease has been reported to be more
severe when meadow nematodes (Pratylenchus penetrans) are present. In the North,
soil fumigation is used to control the disease which is both tuber and soil-borne
in these locations. Although Verticillium is frequently isolated from early dying
plants in NEF, the same fields also usually have high populations of sting and/or
root-knot nematodes. Since the aboveground symptoms of early dying are similar to
those associated with sting and root-knot nematode injury, and since both the
disease and nematode problems are controlled by nematicides; the relative impor-
tance of Verticillium as a pathogen in NEF has not been determined. Attempts to
demonstrate persistence of Verticillium in NEF potato soils, however, have been
unsuccessful. This suggests that inoculum for the disease may be limited to that
on incoming seed tubers. It is not known whether any of the parasitic nematodes
found in NEF potato fields predispose potato plants to attack by Verticillium. The
control procedures for early dying disease are the same as those outlined in
Table 1 for nematode control.
Bacterial wilt and tuber brown rot. A soil-borne bacterium, Pseudomonas solana-
cearum causes this disease, which can be more severe when root-knot nematodes are
present. Bacterial wilt (BW) is most severe in NEF when temperatures and preci-
pitation during March are, respectively, above and below normal. Bacterial wilt
was considered to be a major production problem in NEF during the 20's and 30's.
However, since about 1938 the disease has occurred infrequently in NEF, probably
due to the widespread use of the potato cultivars Katahdin (1938-42) and Sebago (1943
-present) which are both BW tolerant. During 1975-77, however, several NEP growers
sustained losses due to BW and tuber brown rot. Losses were associated with (1) use
of cultivars which lacked the BW tolerance of Sebago, particularly when they were
planted during successive seasons; (ii) using nonvolatile nematicides after having
used soil fumigants for several seasons; (iii) relatively warm and dry weather con-
ditions during March. Although additional data are needed on factors affecting
incidence and severity of BW in NEF, the control procedures suggested in Table 1 are
based on available evidence.
Corky ringspot disease (CRS). This disease is caused by tobacco rattle virus (TRV).
In Florida CRS is a disease of the tuber. The virus is transmitted directly to
potato tubers by stubby root nematodes (Trichodorus spp.). Soil fumigation does not
control CRS in NEF; however, the nonvolatile nematicides, Temik and Furadan, effec-
tively reduce both incidence and severity of CRS. Sebago, the standard variety in
NEF, is highly susceptible to CRS as is Red LaSoda. Pungo, Green Mountain, Hudson,
Superior, Plymouth, Merrimack, and USDA seedling B6969-2 are resistant to the
disease in NEF. See the Hastings ARC Research Report PR77-4 for additional details.
Rhizoctonia disease. Rhizoctonia, presumedly R. solani, is present in most NEF
potato and cabbage fields. The fungus can attack and damage the potato plant in
several ways. Emerging stems can be cankered and in severe cases completely rotted
beneath the soil surface, thereby delaying emergence and even reducing stands of
potatoes. Stolons can be attacked and weakened. The fungus has been reported to
infect developing tubers and to cause malformation, cracking, and abnormal russet-
ting. In addition to these quality defects, black microsclerotia (resting bodies'
of Rhizoctonia are often observed adhering to tubers at harvest and have been re-
ferred to as "the dirt which won't wash off." In NEF the types of abnormal growth
and russetting reported to be caused by Rhizoctonia have been reduced following use
of nematicides. Also, Rhizoctonia has been frequently associated with these types
of symptoms when they occur. In addition, however, numbers of sting nematodes
observed in soil have shown a highly significant positive correlation with the same
type of tuber quality defects. It is not clear whether Rhizoctonia or nematodes are
the primary cause of tuber quality defects in NEF or whether an interaction exists
between Rhizoctonia and the parasitic nematodes; whereby injury caused by nematode
feeding activity predisposes developing tubers to attack by Rhizoctonia. Nemati-
cides, particularly the nonvolatile chemicals such as Temik, Furadan, and Mocap,
have consistently reduced tuber quality defects similar to those associated with
Rhizoctonia. We have no evidence that these chemicals reduce cankering of emerging
plants or of stolons.
The chemicals. Chemicals used for nematode control in NEF can be grouped into two
Jar.egories, soil fumigants and nonvolatile nematicides, depending upon whether or
not they volatilize after application and form a gas in soil. Soil fumigants in-
clude such chemicals as Telone, D-D, Telone II, Vidden D, W-85, Terr-O-cide, and
Vorlex. Nonvolatile chemicals which are registered for use on potatoes in NEF in-
clude Temik, Furadan, and Mocap. Temik and Furadan are carbamates and Mocap is an
organophosphate. All are highly toxic.
The effectiveness of soil fumigants is improved when the soil is rela-
tively dry. The optimum soil moisture for use of soil fumigants in the sandy flat-
woods soils found in NEP is less than 5%, however, some nematode control is observed
even when soil moisture is approximately < 12-15%. Nonvolatile chemicals work best
when soil is relatively moist. Best control is achieved when soil is approximately
A strategy for controlling nematodes and soil-borne diseases on potatoes in NEF. -
Based on information summarized above, a control system for potatoes is presented in
Table 1. The suggestions summarized in Table 1 are based on currently existing data
and changes may be dictated by further research, particularly those related to soil
Table 1. A summary of grower options for controlling nematodes and soil-borne
diseases associated with nematodes.
Table Stock Chip Stock
Soil Moisture-/ Soil Moisture
Disease Problem below 12-151/ above 12-15% below 12-15% above 12-15%
F TF F TF
Nematodes only or or or
F + TF M M
RC +F TF RC + F RC +TF
or or or
Nematodes + CRS F + TF RC + TF RC + M
RC + M TF
Nematodes RW + F RW + I RW + F RW + F*
+ or or
Bacterial wilt RW + RW + M
Nematodes + CRS
RW + F + TP
RCP + F 4 IF
WA + F
RWA + F + TF
RIA + WT
~ A 3
F = Soil fumigation (DO, '[inlore
'F Temik 150 or Furadan 100
M i Mocap 100
II, W-85, Varlex, Terr-O-cide, etc.)
= Resistance Bacterial wilt [(A) Sebago, (B) Green Mountain]
= Resistance CRS [(A) Pungo, (B) Superior, (C) Hudson, (D) Plymouth,
(E) Merrimack, (F) Green Mountain]. Only F is known to
possess tolerance to bacterial wilt.
Use only if TF or M were used in the same field during the previous season.
% soil moisture = Soil wet Soil dry
as % of dry weight weight weight
Soil dry weight
2/ Use Cautions:
...Do not use Furadan 10G within 18 months of planting crops on which it
is not registered.
...Do not apply Mocap 10G in-furrow. Mocap can cause injury on sorghum
...Do not apply at plant applications of Temik 15G within 90 days of
...Ethylene dibromide has caused injury on potatoes in NEF when applied
when soil was cold and wet.
...Use all chemicals in strict accordance to the instructions on the label.
...Do not plant Superior, Pungo, Red LaSoda, or Atlantic (or other un-
tested cultivars) in fields with a past history of bacterial wilt and
tuber brown rot.