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POTATO
(TOMATO) PSYLLID
Outbreaks
of potato psyllids (Paratrioza cockerelli) are very sporadic but
have occurred suddenly and over vast areas. Psyllids are most found
from the Rio Grande River valley and north in the High Plains States.
They are very small insects, the adults are about the size of the
head of a pin while the damaging nymph is closer in size to the
point of a pin. The damage to plants is due to the injection of
toxin produced by the insect into the plant during its feeding.
Description
Potato
psyllids go through three stages in their development - adult, egg
and nymph. The nymph is the cause of problems on the plant.
Adults,
nicknamed “jumping plant lice,” are not damaging. They look like
a tiny cicada for those familiar with this noisy insect and will
jump and fly when slightly disturbed. Adults are about a tenth of
an inch long with wings held roof-like over the body. Initially
light green for their first three days, they turn black with white
markings, usually stripes. Their eyes are bulging or prominent and
their legs are well developed.
Eggs
are orange-yellow and appear at the end of short stalks, similar
to but much smaller than the white eggs of lacewings (not a common
predator). Eggs appear in clumps and usually, but not exclusively,
on the underside of apical leaves.
 Nymphs
are the damaging form of this insect. They are tiny (pin-head) and
flat. Their most notable appearance is that they look like overlapping
scales (reminding me of a tiny trilobite of the Paleozoic Era).
This scale-like appearance is ringed with tiny hairs. Young nymphs
are pale brown and turning pale green with successive molting. There
are four (five instars) molts until adult metamorphosis. Nymphs
are mostly found in the upper canopy and on the underside of leaves.
Nymphs are quiescent and, unlike aphid nymphs, do not move around
much. Nymphs excrete a waxy salt-like or sugar-like white granular
substance. They are sucking-type insects, but their damage is NOT
due to feeding but due to the secretion of a toxin into the plant
with their saliva. This toxin affects growth of all the plant’s
parts and causes a symptom called “psyllid yellows.” Toxin occurrence
in nymphs is irregular as it seems to an inherited trait. So the
presence of psyllid nympphs does not necessarily mean that psyllid
yellows will occur. Potato psyllids do NOT seem to be vectors of
haywire, potato leaf roll nor aster yellow.
Life
Cycle
Adults
overwinter along the Rio Grande River region and migrate north in
the spring. Along the way, they lay eggs. Over 500 eggs may be laid
during an average period of 21 days. Eggs hatch within a few days.
Nymphs can survive up to 90 days but usually last only two to three
weeks before changing to adults. The entire cycle usually is four
to five weeks but this varies considerably depending on host and
temperature. There are usually three to four generations per season
but fewer as insect migrates further north. Generations may overlap.
Appearance of psyllids further north depends on winds starting in
June and July.
Population
Dynamics
Although
most commonly outbreaks occur in Texas, New Mexico, Arizona, Colorado
and California, they have been reported as far north as Alberta
and Saskatchewan. Potato psyllids overwinter exclusively on winter
hosts along the Rio Grande River Valley, on the southern borders
of Texas, New Mexico and Arizona. Populations increase from January
to May. Peak populations occur at the end of April and early May.
They appear north due to migrations of adults. They have appeared
consistently in lower and middle High Plains States and in 1998
were reported in South Dakota. Most of the research and available
information on this insect pest comes from Colorado and Texas. For
a historical perspective, some severe outbreaks in Nebraska, Colorado
and Wyoming have been reported.
Hill,
R.E. 1947. An unusual weather sequence accompanying the severe potato
psyllid outbreak in 1938 in Nebraska. J Kans Entomol Soc 20:88-92.
Starr,
L.A. 1938. Psyllid yellows unusually severe in Wyoming. Plant Disease
Repr 23:2-3.
Wallis,
R.L. 1946. Seasonal occurrence of the potato psyllid in the North
Platte Valley. J Econ Entomol 39:689-694.
Potato
psyllid can live on or survive on a plethora of hosts. Their main
economically important hosts are potato and tomato. However, most
members of the Solanaceous family such as pepper, eggplant, and
weeds such as nightshades can be hosts. Also, psyllids can survive
on many non-Solanaceous weeds such as pigweeds, lambsquarter and
bindweed.
Temperature
is a critical factor in psyllid outbreaks and range. They do not
like very high temperatures, preferring 80 F. Two hours at 100 F
is lethal to eggs and nymphs. Temperatures above 90 F will reduce
or cease egg laying, hatching and nymph survival. For this reason,
psyllids like high altitudes, above 5900 ft. However, their northerly
migration seems to be limited by cooler fall temperatures and possibly
a reduction in radiance as the autumnal equinox approaches.
Insect
Monitoring
In
spring, potato psyllids are first found on perennial weedy hosts
such as matrimony vine and on greenhouse Solanaceous plants particularly
pepper and tomato. Early sprouting potato cull piles also attract
the psyllids and these cull piles can then act as a source for potato
field infestations. In potato fields, the potato psyllid does not
distribute itself uniformly. They typically appear on the edge of
the field like Colorado potato beetles, usually the southern rim,
and progress toward the center. Yellow pan traps used to monitor
green peach aphids will pick up psyllid migrations. Winged black
adults can also be picked up using yellow sticky cards hung close
to the canopy. Due to the unpredictability of adult migrations and
nymph’s toxin inheritance, and toxin effects, no population thresholds
have been set for economic levels or treatments.
Damage
- Psyllid Yellows
Potato
psyllid nymphs attach to the underside of leaves and feed by sucking
plant juices, sap, through needle-like mouth parts; this in itself
doesn’t cause enough damage to be the concern. But, many nymphs
have inherited a gene that causes them to produce a plant poison
(phytotoxin) which is injected into the plant in the nymph’s saliva,
similar to a mosquito, and drastically reduces or even ceases all
plant growth. The degree of damage depends on the amount of toxin,
related to insect infestation, and the plant’s growth stage. Variability
between cultivars with regard to susceptibility and symptom expression
has been suggested, but still unclear, and maybe more related to
seasonal maturity type then actual tolerance.
Arslan,
A., Bessey, P.M., Matsuda, K. and Oebker, N.F. 1985. Pysiological
effect of psyllid on potato. Amer Potato J 62:9-22.
Foliar
Symptoms (“Psyllid Yellows”):
Toxic
symptoms may appear as quick as four to six days after injection
in a heavy infestation but usually it takes two to three weeks.
When plant are young, still in vine growth, they will be stunted
and chlorotic (yellow from lack of chlorophyll). Internodes will
be shorter causing a rosette canopy appearance and nodes will thicken.
Occasionally, aerial tubers will appear at nodes.
 For
field diagnostics, the first and most easily spotted foliar symptom
is a distinctive leaf roll (“feathery appearance”) especially in
conjunction with yellowing of the upper leaves (see photo). From
a distance, this leaf roll looks similar to that symptomatic of
black leg, leaf roll virus and Eur. corn borer. But, even without
finding the nymphs, the others may be eliminated by looking for
the black, slimy stem base associated with black leg, and for the
entry hole and fraas associated with the corn borer. Also, unlike
leaf roll virus, the leaves are not brittle and do not produce a
soft rattle when shaken. The leaf roll is looser with the leaflets
are often slightly jagged from irregular growth and the basal part
of leaflets are more curled upward. Leaves, especially the younger
leaves may have a purple tinge (anthocyanin pigmentation). In some
cases, veins may also develop a slight purple tinge in older leaves.
Besides
being affected by nymph density, saliva toxicity and feeding duration,
several other factors influence expression of foliar symptoms. Higher
intensity and longer duration of sunlight will enhance symptom expression.
Therefore, the high light intensity and moderate summer temperatures
in high mountain valleys as in Colorado are very conducive to psyllid
yellows. Symptom expression is also increased in plants in alkaline
soils as in the Nebraska Panhandle and by an abundance of irrigation
common under center-pivots. Older plants are more tolerant of psyllid
infestation and the phytotoxin has a lesser effect since canopy
growth is completed but tubers will still be affected unless fully
mature.
Tuber
Symptoms:
 Potato
psyllids have a major (big time) impact on yields, the earlier the
infestation with regard to tuber growth the greater the yield reduction.
Also the severity of yield loss is proportional to the severity
of foliar injury. Total yield losses are due to a reduction in tuber
size. When infestation is in early bulking, tuber growth is affected
more than when infestation is in late bulking. In addition to smaller
tubers, there is an increase in the number of tubers and their set
is closer to the plant stem, shorter stolons. Furthermore, tubers
tend to be mis-shaped and have a rough skin.
Another
important tuber characteristic is a loss of dormancy resulting in
premature sprouting. Therefore, tuber chaining and internal sprouting
are common. Sprouts are spindly, “hair” sprouts, and very weak.
These tubers are unacceptable for the following year’s planting.
Internal necrosis also may occur but, on the other hand, starch
and sugar content are not adversely affected by the phytotoxin.
Reversibility:
Removal
of nymphs when the first signs of symptoms seems to allow for recovery
of plants. From the Univ. Arizona, there is a report (Arslan et
al., 1985) that, after a planting application of phorate (Thimet),
a foliar application of methomyl (Lannate), shortly after infestation
at six to seven weeks after emergence, partially reversed the phytotoxicity
caused by the psyllids (Figure 1). Note depicted is total yield;
marketable yield will be lower as some tubers will still mis-shaped
and have sprouting defects.
Control
Chemical
-- There are many insecticides that will affect potato psyllids.
It is best to use a systemic. The main difficulty in treating for
them is that the nymphs are on the leaflet’s underside and don’t
like to move; therefore, foliar treatments work best when the undersides
are exposed. The best foliar applications are low-flying, high-volume
aerial spraying and ground spraying using drop nozzles. Common foliar
products are Actara, Ambush, Asana, Leverage, Monitor, Phaser, Pounce,
Provado and Thiodan. Traditionally, systemic insecticides, Di-Syston
and Thimet, were applied at planting but there short residual activity
limit their effectiveness. Newer at-planting systemic insecticides,
Admire (imidacloprid) and Platinum (thiamethoxam), with their much
longer residual, about 13 weeks, have shown to be very effective
against psyllids and other insects (Figure 2). Newer still is the
use of the active ingredient in these products as seed treatments
either as a dust, Tops MZ Gaucho and soon to be released Maxim MZ
Cruiser, or as a liquid, Genesis. These treatments seem also to
be highly effective against potato psyllids and leafhoppers (Figures
2 and 3).
Effect
of Seed and In-furrow Treatments on Potato Psyllid Symptoms on Potato
Plants in 2001 at Scottsbluff, NE.
| Seed
Treatment |
In-Furrow
Treatment |
Leaf
Roll
% Plants |
Yield
of US #1
cwt/acre |
| Maxim
MZ 10.1D1 |
none |
30
A2 |
322
B |
| Maxim
MZ 10.1D |
Platinum
2SC |
0.7
B |
368A |
| Maxim
MZ Adage |
none |
0.7
B |
389
A |
| Tops
MZ 2.5D |
none |
25
A |
325
B |
| Tops
MZ 2.5D |
Admire
2F |
0.7
B |
390
A |
| Tops
MZ Gaucho |
none |
1.4
B |
377
A |
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1
Maxim MZ treatments applied at 8 oz/cwt, Tops MZ at 12 oz/cwt,
Admire at 1.3 fluid oz/1000 linear feet, and Platinum at 0.55 fluid
oz/1000 linear feet.
2 Treatments in columns followed by different letters
were significantly different from each other at p=0.05.
Biological
-- There are a number of natural predators that feed on psyllids.
These are the convergent lady beetle, minute pirate bug and damsel
bug. But, although they are good eaters and will eat any stage of
psyllid development, their effect on populations is modest and far
less important than weather conditions. There is also a parasitic
wasp that will paralyze nymphs and lay their eggs in them. But,
field studies show that they are not well synchronized with the
psyllid life cycle and therefore do not show much promise.
Quick
Review
Appearance:
- Adult
-- light green when young, black with white markings when older;
1/10 inch long
- Egg
-- orange-yellow
- Nymph
-- pale brown to pale green; tiny, flat, overlapping scales
Life
Cycle:
- Overwinters
in the Rio Grande River region
- Adults
migrate north influenced by wind and temperature
- One
to four generations / season depending on geography, temperature
and host
Damage:
- Adult
-- none
- Nymph
-- injects toxin causing “psyllid yellows” and slows growth of
vine and tubers
Management:
- Beneficial
predators -- lady beetles, pirate bug and damsel bug
- At-planting
insecticides -- imidacloprid and thiamethoxam
- Foliar
treatments
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