;TATE PLANt BEOARP
E-532 \ DER ENT March 1941
(( BUREAU Of )
\\ENTOMOLOGY AND /
^PLANT QUARANTINE ^
THV POTATO AND TOMATO PSYLLID
By R. L. Wallis, Division of Truck Crop and Garden
The potato and tomato psyllid (Paratrioza cockerelli (Sulc)) is
one of the most injurious insects affecting potato and tomato crops in the
Western States. While feeding, the psyllid nymphs inject into these plants
a secretion which causes the disease known as psyllid yellows. The nature
of this secretion is not definitely known, but the physiological balance of
the plant is upset, and this, in potato, prevents the proper translocation of
sugar from the leaves, where it is manufactured, to the tubers, where it is
stored as starch. It is this nymphal stage of the insect with which the
grower should be particularly acquainted, since it is the stage that causes
the damage to the growing plants. Psyllid yellows, often confused with other
diseases having similar symptoms, appears suddenly in epidemic years, making
difficult the application of control measures in time to prevent serious
The losses from damage by the psyllid are difficult to estimate,
owing to the great variation in severity of attack from year to year and
from one locality to another. If potato plants are severely attacked in
the early stages of growth before tubers have started to form, a very large
number of small tubers will be set, sometimes at intervals along each
stolon, none of which will reach a marketable size. If the plants are
attacked after the tubers are set, the growth of the tubers will be retarded,
the yield of the crop will be reduced, and the tubers will be of poor qual-
ity. In fact, the immature tubers may even sprout and produce new vines,
or they may sprout during storage. The effects of psyllid yellows on
potato plants and tubers are shown in figures 1 and 2.
This publication brings together and summarizes from several sources
the more important available information relative to the potato and tomato
psyllid and its control, and has been prepared primarily for distribution
to interested growers.
Total crop failures of potatoes have been reported in many cases,
particularly in epidemic years, and serious losses have occurred nearly
every year in many fields. Daniels (1)2 estimates that the loss to potato
growers in Colorado in 1931 was more than $2,763,200. Richards and Blood (5)
estimate that in Utah in 1927 losses of from 25 to 30 percent of the crop
occurred, amounting to approximately $750,000. These records are for
epidemic years, but reports show that total crop failures may occur in some
localities almost every year.
The higher altitudes where psyllids appear more abundantly are not
suited to the commercial production of tomatoes. In lower altitudes, how-
ever, the tomato crop i1 a complete failure -in some years from psyllid
yellows. As with potatoes, the severity of damage to tomatoes varies
greatly, ranging from slight decreases in yield to total crop failures,
depending on the season. Young plants suffering from the disease may be
stunted and fail to set fruit. The fruit which is set is of low quality,
the pulp being coarse and rubbery in extreme cases and low in juice content.
The fruit takes on an undesirable yellowish color.
SYMPTOMS OF PSYLLID YELLOWS
Psyllid yellov.ws (sometimes incorrectly called "purple top") is dif-
ficult to distinguish from several other diseases, such as leaf roll and
rhizoctonia, because of a close similarity in symptoms. The first symptoms
of psyllid yellows in potatoes are an upward curling of the basal portion
of the terminal leaves and a change in color to light green or yellow.
As the disease develops, the curling extends toward the tip of the leaf,
and the curled portion of the leaf turns to a reddish-purple color, particu-
larly in varieties carrying the red pigment. The leaves feel harsh or
"leathery" to the touch. In the advanced stage of the disease, the yellow
becomes more pronounced, deepening to a brown at the death of the plant.
Plant growth is retarded, and aerial tubers may form in the leaf axils;
On tomatoes, the disease symptoms are an upward curling and thickening
of the older leaves. The color usually becomes a yellowish green, with a
slight purpling of the veins of the younger leaves. The terminal leaves are
stunted and never reach a normal size. If the plant is attacked when small,
the entire plant may be stunted and may fail entirely to set fruit.
DISTRIBUTION OF THE POTATO AND TOMATO PSYLLID
Reports show that the potato and tomato psyllid occurs in North
Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas, and all States
west of these, with the exception of Washington and Oregon, as well as in
western Canada. It may also occur in Minnesota, Iowa, and some of the
adjacent States. Little is known about the climatic factors governing
2 Numbers in parentheses refer to Literature Cited, at the back of
this circular. .-
or limiting the distribution of the psyllid. However, it is usually found
to be more abundant during the summer at the higher elevations where cooler
weather predominates. Eearly planted crops grown in the cooler part of the
season are more susceptible to attack than those grown late in the season
when temperatures are higher. In the Southwestern States, potatoes are
grown in the spring and harvested in June before the occurrence of high
summer temperatures and are therefore susceptible to attack. In these
States tomatoes are grown in the summer months and are not so susceptible
to attack, apparently because the high temperatures are unfavorable for
breeding of the psyllid.
Theegg.--The egg (fig. 3) is about 1/32 inch in length, elliptical
in shape, and light yellow, this color deepening to orange as the egg ap-
proaches the hatching stage. It is usually placed on the edge or under
side of the leaf and is attached by a short stalk or stype which is about
the length of the egg. The eggs, if numerous, may be seen with the naked
eye on the edge of the leaf if held in the bright light. They may be con-
fused with the pale-green eggs of lacewing flies, which are larger and have a
longer stype. The larvae of lacewing flies are predacious upon the eggs and
nymphs of the psyllids, as well as upon other small insects.
Deposited singly, the eggs laid by 1 female psyllid in 1 day will
often be found on 1 or 2 leaves. Knowlton and Janes (2) found that females
deposited from 5 to 157 eggs during 24 hours, with an average of about 37.
The total number of eggs laid by each female is probably about 300 to 400.
The incubation period for the eggs varies greatly with temperature; usually
it is from 3 to 8 days but may be longer if the weather is cool.
The nymph.--The nymphs (fig. 3) are small, flat, scalelike insects,
which vary in color from light green to orange. They are quite inactive
and normally take up a position on the under side of the leaf, where they
feed. A band of short hairs or spines protrudes from around the entire
margin of the body. A row of wax glands secrete a white wax, and when
nymphs are abundant this wax may be seen on the. leaves and on the ground
around the plant.
During their development the nymphs pass through five instars.
Knowlton and Janes (2) found that the first instar required from 1 to 5
days, with an average of 2.76 days; the second required from 1 to 4 days,
with an average of 2.72 days; and the fifth required from 3 to 9 days, with
an average of 4.87 days. In the later instars the nymphs are large enough
to be seen by the unaided eye. They develop directly from the last nymphal
instar into the adult stage without going through a pupal stage. Throughout
the nymphal stage they remain on the under side of the leaf, feeding upon
it and injecting into it a secretion which is toxic to the plant and causes
The adult.-The adult (fig. 3) is about 1/10 inch in length and re-
sembles a miniature cicada or 17-year locust. The general color is gray,
with white bands on the head. thorax, and abdomen. There is a broad,
transverse, white band at the base of the abdomen and a Y-shaped white mark
at the tip. When resting, the wings are held in a rooflike position over
the abdomen. When they first emerge, the adults are light green, but be-
come the normal grayish color after 2 or 3 days.
There is considerable variation in the length of life in the adult
stage. Knowlton and Janes (2) found under laboratory conditions that some
adults lived only a day or two while the longest record for a male was 64
days and for a female 189 days. They also found that the length of the
oviposition period ranged from 1 to 179 days, with an average of 21.45 days.
The adults have legs that are fitted for jumping, and on the least
disturbance they will jump and take flight. This movement is so fast as to
be unnoticed and is the reason that the adults are hard to find on plants
in the field. They are sometimes called jumping plant lice, because of
their resemblance to plant lice and their jumping habit.
The host plants of the potato and tomato psyllid belong principally
to the nightshade family (Solanaceae). The most important of the cultivated
plants are potatoes and tomatoes, although peppers, eggplants. Jerusalem
cherries cultivated ground cherries, ornamental peppers, and matrimony
vines will serve as breeding plants. Among the wild host plants the most
important are probably the several species of ground cherry, buffalo bur,
wild tomato, several species of Lycium, and other nightshades. In the fall
of the year, after frost has killed their preferred food plants, the psyllid
may be found on almost any plant remaining green.
FACTORS AFFECTING SEASONAL ABUNDANCE
Hibernation.-The potato and tomato psyllid overwinters in the adult
stdge, but as to the place of overwintering more definite information is
needed. Daniels (1) records the psyllid as overwintering in red cedar areas
in southwestern Nebraska. However, from extensive sampling during the
winter of 1939-40 r:id the fall of 1940, the writer was unable to find any
adults of the psyllid on red cedar in the North Platte River Valley in
Nebraska and Wyomiiy,. Romney (6) found the psyllid breeding on Lycium
along, the Rio Grande draiiiage above Laredo, Tex., for several hundred miles,
and he believes that there is a possibility that this is the main source of
the spring infestations that occur east of the Divide as far north as
Colorado. If such a migration takes place it is not unlikely that a genera-
tion or two *-ould bre,.'d on native host plants in this intermediate region
and these move north as the season progresses.
Effects of temperiture.--List (4) has shown in laboratory tests that
the optimum temperature for psyllid development is about 80 F., with greater
development below than dhove that point. Also, oviposition, hatching, and
survival are definitely reduced under 90 constant temperature, while a
- 5 -
temperature of 95 for only 2 or 3 hours a day will permit little if any
increase in numbers, and a temperature of 100 for 1 or 2 hours of the day
is lethal to eggs and nymphs and practically stops all egg laying. It has
been the writer's observation, during the reasons of 1939 and 1940 in the
North Platte Valley of Nebraska and Wyoming, that population increases occur
during June, late August, and September, but during July, when maximum daily
temperatures are around 100 F. and above, populations definitely drop,
except on early plantings, in which the large vines protect the developing
psyllids from high temperatures. During both these years at Laramie, Wyo.,
where the maximum temperature seldom reaches 90 F., populations continued
to increase throughout each season and reached enormous numbers by September.
Romney (6) states that adults move completely from native host plants in
southern Arizona by the middle of June, and thereafter it is not possible
to find psyllids in this area until late in October or early in November,
and suggests that probably the most important factor causing this is the
shedding of the leaves of the host plants due to lack of moisture. It is
not unlikely that the high summer temperatures also play an important part
in this cessation of breeding.
Natural enemies.--Certain parasites and predators of the potato and
tomato psyllid have been observed, but little is known as to their effective-
ness, although observations indicate that they may play an important part
in causing the great fluctuations in psyllid population which occur from
one season to another. One parasite (Tetrastichus sp.) has been observed
feeding on psyllid nymphs, and several predators such as ladybird beetles,
several hemipterous insects, and larvae of lacewing flies have been observed
feeding on eggs and nymphs.
On potatoes.--The control for the psyllids on potatoes, as worked out
by the Colorado Agricultural Experiment Station, is a spray consisting of 1
gallon of concentrated lime-sulfur (32 degrees Baum6 test) to 40 gallons of
water, or, if preferred, 4 or 5 pounds of dry lime-sulfur to 40 gallons of
water may be used. The liquid form is better since it goes into solution
more completely and the commercial product is fairly well standardized.
In applying the spray not less than 250 pounds and preferably 350 pounds or
more pressure should be used. Sprayers powered either by a tractor or a
separate motor should be used, since it is very difficult to secure the
necessary pressure with traction sprayers. Thorough plant coverage by the
spray, particularly on the under sides of the leaves, should be obtained,
since this is normally where the psyllid nymphs feed. This can be accom-
plished best by using three nozzles to the row, one being placed above and
one on each side of the row. The side nozzles should be set close to the
ground and directed upward at a 45-degree angle. One of the side nozzles
should be set to spray slightly in front of the spray boom, and the other
slightly behind, as this permits the foliage to be blown from one side to
the other, giving a better coverage by the spray.
The proper time to make spray applications is still a debatable
question. The size and habits of the adults and nymphs make it difficult
to observe them on the plants, and their presence is often unnoticed until
large numbers are present and considerable damage has resulted. Richards (5)
has shown that approximately 15 nymphs per plant are necessary to produce
psyllid yellows on potatoes, but it is difficult to make nymph counts under
field conditions. It has been the writer's observation that when adult
populations reacd 6 to 8 per 100 sweeps of a standard insect net, psyllid
yellows symptoms will begin to appear in from 7 to 10 days. If population
counts are to be used as a basis for determining the time for making spray
applications, it is believed that, as a measure of safety, application
should begin when 3 or 4 adults to the hundred sweeps are found. If popu-
lation counts of the psyllid cannot be used for timing treatment, the first
spray application should be made when the plants are 6 to 8 inches high and
the second 2 or 3 weeks later. In some seasons a third application should
be made 2 or 3 weeks after the second. A good practice is to make at least
two applications each season, and be prepared to make subsequent applications
if the need exists.
If the Colorado potato beetle or flea beetles are present, 2 pounds of
zinc arsenite should be added to each 40 gallons of the spray mixture.
The cost of spraying potatoes with lime-sulfur is approximately
$2.50 per acre for two applications, taking into consideration the cost of
the material, labor, and machinery.
On tomatoes.--To control the psyllid on tomatoes, List (3) recommends
the use of (1) 300-mesh dusting sulfur undiluted; (2) 300-mesh wettable sul-
fur, 1 pound to 10 gallons of water (1 heaping tablespoonful to 1 gallon of
water); or (3) 1 gallon of 32 degrees Baume liquid lime-sulfur and 4 pounds
of 300-mesh wettable sulfur to 80 gallons of water (3 tablespoonfuls of
liquid lime-sulfur and 1 tablespoonful of wettable sulfur to 1 gallon of
water). The plants should be treated 10 days before leaving the coldframe
or greenhouse. If this has not been done, the tops of the plants should be
dipped at setting time in a mixture of 1 ounce of wettable sulfur to 1
gallon of water. The plants should be treated 10 days after transplanting
to the field; again when the plants are branching freely and beginning to
bloom; and finally just before the plants break over and begin to spread.
(1) Daniels, Leslie B. 1937. Controlling Colorado Potato Pests. Colo.
Agr. Expt. Sta. Bul. No. 437. 35 pp., illus.
(2) Knowlton, G. F., and M. J. Janes. 1931. Studies on the Biology of
PardtrLioza cockerelli (Sulc). Ann. Ent. Soc. Amer: 24 (2): 283-291,
(3j List, George M. 1939. The Potato and Tomato Psyllid and its Control
on Tomatoes. Colo,. Agr. Expt. Sta. Bul. 454. 33 pp.
(4) List. George M. 1939. The Effect of Temperature upon Egg Deposition,
Egg Hatch and Nymphal Development of Paratrioza cockerelli (Sulc).
Jour. Econ. Ent. 32 (1): 30-36.
(5) Richards, B. L. anid H. L. Blood. 1933. Psyllid Yellows of the
'Potato. Jour. Agr. Ces. 46 (3): 189-216, illus.
(6) RomTLey, V. E. 1939. Breeding Areas of the Tomato Psyllid, Paratrioza
cockerelli (Sulc). Jour. Econ. Ent. 32 (1): 150-151.
Figure 1.-Normal and psyllid-damaged potato plants. Note the
dwarfing of the top of the potato plant on the right as
compared with the irregular, bushy shape of the healthy plant
on the left.
Figure 2.-Effect on tubers of a psyllid-damaged potato plant.
SmvrM pLANT DOAR"
Figure 3.-Life stages of the potato and tomato psyllid: Adult (at top),
egg (left center), and five stages of nmphs. All greatly enlarged.
UNIVERSITY OF FLORIDA
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