Quick Facts...
- The potato/tomato psyllid secretes a toxic saliva during feeding that
can severely damage potatoes and tomatoes.
- Psyllids do not overwinter in Colorado. Outbreaks occur from flights
of psyllids that migrate from southern states and Mexico.
- Check potatoes and tomatoes each year for psyllid problems. If psyllids
are detected, promptly treat affected plants with an insecticide.
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Figure 1. Potato psyllid adult..
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Life Cycle
Potato/tomato psyllids pass through three life stages: egg, nymph (immature
stage) and adult. The adult psyllid is about the size of a typical aphid
and is a member of the insect family known as "jumping plant lice." Adult
psyllids are rarely found in Gardens unless collected with a sweep net
or knocked onto a cloth placed around the base of the plants. If seen,
adult psyllids are striped with alternating dark and light bands.
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| Figure 2. Eggs, nymphs and adult potato psyllid. |
Eggs are small, 1/32 inch long. They are orange-yellow and supported
by small stalks. They are much smaller than the stalked, white egg produced
by lacewings, which also are common in Gardens. Psyllid eggs are frequently
deposited along leaf margins but may occur on either leaf surface. Eggs
hatch in six to 10 days.
Newly hatched nymphs are yellowish but become progressively greener as
they develop, undergoing four molts. When almost mature, nymphs are nearly
the same color as leaves. Nymphs are flat, elliptical and scale-like.
Nymphs are most numerous on the undersides of leaves but can occur on
shaded upper leaf surfaces. They are inactive and seldom can be seen to
move about. While feeding, psyllid nymphs excrete small, waxy beads of
"psyllid sugar," which resembles granulated sugar. This material may cover
leaves during heavy psyllid infestations. The nymph stage usually lasts
from 14 to 22 days. Newly emerged adults remain green for a day or so
before turning darker.
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| Figure 3. Psyllid sugar and nymphs. |
Potato/tomato psyllids do not overwinter in Colorado but survive on certain
plants growing in southern Texas, New Mexico and Arizona. Problems with
psyllids originate each season from winged, migrating forms of the insect.
Psyllid outbreaks are irregular, depending on weather conditions.
Psyllids usually are found first on early potatoes or pepper transplants.
Throughout the season, adult psyllids move to new plants, becoming most
numerous late in the season on tomatoes. The number of psyllid generations
produced during a year is thought to vary from four to seven. However,
there is much overlap of the generations after the original infestations
become established.
Insect Injury
Adults and nymphs feed by sucking plant juices. Feeding by nymphs is
especially serious because it brings about an abnormal condition known
as "psyllid yellows," a result of toxic saliva injected by the insect.
The symptoms on potato and tomato plants are generally similar. Usually
the first abnormal condition is a slight discoloration (yellowing or purpling)
along the midribs and the edges of the top leaves. The basal portions
of these leaves tend to curl upward.
As the condition progresses, the entire plant top changes to yellowish-green
or purple-red, and foliar growth is checked. The leaves remain small and
narrow and tend to stand upright, giving the top of the plant a feathery
appearance.
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| Figure 4. Symptoms of psyllid yellows. |
When the attack comes early in the development of the tomato plant, effects
from psyllid feeding may be so severe that little or no fruit is set.
Late attack on tomato plants is inclined to cause production of an abnormal
number of fruits that never attain a desirable size or quality.
If the attack on potato plants occurs before tuber set, a likely result
is the formation of numerous tubers on each stolon. An attack after tubers
are partially developed usually results in greatly retarded growth and
irregularly shaped potatoes. Potatoes from infested plants may sprout
prematurely, even underground before harvest.
Psyllids also occur on other plants in the potato family, such as eggplant
and pepper. Damage to these Crops is insignificant.
Control
Because these Insects are so small, damage to tomatoes or potatoes frequently
occurs before the problem is detected. It is important to be able to identify
potato/tomato psyllids so developing problems can be detected and treated
in time. One of the most important means of identification is the psyllid
sugar that is excreted by the insect and collects on leaves. Psyllid problems
do not occur every season. In some areas of the state, Extension
pest alerts provide warnings of psyllid outbreaks.
Homeowners not able to properly identify psyllids may wish to routinely
treat susceptible plants. Protectant treatments may be needed from when
plants are 6 inches tall until midsummer. Well-established plants with
abundant foliage usually can tolerate late season infestations with little
yield loss.
Among insecticides available to homeowners, products containing permethrin
or esfenvalerate are most effective when used at rates labelled for other
potato/tomato insects. Alternately dusts of sulfur can provide control.
Regardless, application must be thorough, covering the underside of lower
leaves where the insects tend to concentrate. Insecticidal soaps (two
percent concentration) may also be useful, although control is more erratic.
Some tomato varieties appear to be partially resistant to potato/tomato
psyllids. Increased hairiness of the leaves is reported to make plants
less favored by psyllids.
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