Master Gardeners of Ventura County
University of California
Master Gardeners of Ventura County

Tomato Psyllid Infestation

PLANTS AND PESTS, JUNE 2005
“TOMATO PSYLLID INFESTATION”
BY
VINCENT LAZANEO
Home Horticulture Advisor
San Diego County
A small insect could take a big bite out of the tomato harvest from home gardens this summer. The tomato psyllid has devastated commercial tomato fields since it showed up in Baja California a few years ago. It has now reached San Diego County, so gardeners should be watchful.
The tomato psyllid {Bactericerca cockerelli} has a wide range of acceptable hosts, including species in twenty plant families. It prefers to feed on tomato, potato, pepper, eggplant, and other plants in the night shade or solanaceae family. The name tomato psyllid is commonly used, but the pest is also known as potato psyllid when it feeds on potatoes. The psyllid uses its piercing mouth parts to extract plant juices from foliage. Excess sugar which the insect ingests, is excreted as small waxy beads of psyllid sugar (resembling granulated sugar).
Psyllid nymphs and possibly adults, inject toxic saliva into plant foliage. The feeding damage on tomatoes and potatoes is especially serious because it causes an abnormal condition known as “psyllid yellows”. Young tomato transplants may be killed by this toxin. Older pre-flowering plants become stunted and chlorotic. Little or no fruit is set when plants are attacked early in their development. Attacks which occur later often cause plants to produce an abnormally large number of small, poor quality fruit.
In northern areas of the United States, cold weather during winter kills psyllids and many of the host plants they feed on. The insect lives throughout the year in Southern Texas and Mexico where winters are mild. Adult psyllids migrate northward during spring and summer and can be carried great distances by wind currents. The psyllid has historically spread annually into Northern Texas, New Mexico, and Arizona, then to Nebraska, Colorado, and Montana. Until a few years ago, the tomato psyllid was not considered a major pest in California. Outbreaks in the state were recorded for a single year in 1940 and again in 1970.
A new series of outbreaks began in 2001 and has occurred every year since then. Scientists initially thought that psyllids from southern Texas had migrated to the west coast, but DNA tests of the insects have shown that the two populations are different. A severe outbreak in Baja California during 2001 destroyed 85 percent of mature tomato plants on commercial farms and crop losses were even higher. There was less damage last year, but Baja farmers still lost 20 to 75 percent of their tomato crop. The psyllid also spread into California last summer and damaged tomatoes in fields as far north as Santa Maria and Hollister (South of San Jose).
Surprisingly, home gardeners in San Diego County did not report any psyllid damage on tomatoes during the last four years. The psyllid probably attacked some back yard tomatoes last year, but gardeners likely attributed any damage to other causes. Home garden tomatoes are more likely to be damaged by the psyllid this year, because the pest lived through the winter in some areas of the county, and the summer migration of psyllids from Mexico has already begun. In early June, strong winds blew adult psyllids north from Baja California, when a weather system called the Catalina Eddy formed off-shore. University of California entomologist John Trumble said “adult psyllids fell out of the sky like rain over San Diego and other areas of Southern California.”
These migrating psyllids are only the latest to arrive in the county. In April, U.C. Master Gardener Charles Robinson found tomato psyllids on tree mallow (Lavatera species) at his home in San Diego. The psyllid belongs to the insect family known as “jumping plant lice” and Robinson said “dozens of them jumped on to my clothes” when he inspected another heavily infested plant about a mile from his home. U.C. Master Gardener Leta Bender also found the psyllid on tree mallow and mallow (Malva species) at her home in Jamul.
Psyllid populations can develop quickly, especially during warm weather. Each adult female can produce more than a thousand eggs, which are laid mainly on the undersides of leaves and along leaf margins. A magnifying glass is a helpful tool to see the eggs, which are about 1/32nd of an inch long. They are orange-yellow in color and held above the leaf on a small, hair-like stalk. A beneficial insect, the green lacewing, also lays its eggs on stalks, but they are white and much larger than psyllid eggs.
Small nymphs hatch from the eggs in four to fifteen days, depending on the temperature. Newly hatched nymphs are yellowish to orange green in color, and turn greener as they grow. At maturity, they are almost the same color as tomato leaves. The flat, scale-like nymphs, have short legs, but only move when they are disturbed. The nymphs molt four times as they grow, and become adults in two to three weeks.
The adult psyllid is a 1/8 inch long winged insect about the size of a typical aphid and looks like a tiny cicada. It has clear wings with alternating light and dark bands on its body. The small size of tomato psyllids makes them difficult to detect on tomato plants, and severe crop damage can occur if an infestation is not treated in time. Yellow sticky cards, which attract adult psyllids, can be used to monitor the pests’ arrival in a garden. Place the yellow, sticky traps near the tops of tomato plants and check them weekly for adult psyllids. Infestations can also be detected by the presence of psyllid sugar – excreted by the insect – which collects on leaves.
Abnormal foliage color can also indicate an infestation. The first symptom usually seen is a slight yellow or purple discoloration along the mid-rib and edges of the top leaves. The basal portion of these leaves tend to curl upward. As the condition progresses the entire top of the plant changes to yellowish green or purple-red. The leaves remain small and narrow and tend to stand upright, giving the tops of plants a feathery appearance.
The variety and age of the tomato play a role in the amount of damage that psyllids cause. According to Dr. Trumble, “the yellow pear tomato is a highly favored host,” but the susceptibility of other home garden varieties is not known. . Loss of fruit on young plants is very likely unless an infestation is controlled at an early stage. Well established plants with abundant foliage may be able to tolerate late season infestations with little crop loss.
Gardeners can do a few things to protect their tomatoes from psyllid damage. Perennial host plants like mallow and tree mallow which tomato psyllids live on throughout the year should not be grown. Also, do not grow any annual host plants for as long as possible during late winter. This will kill psyllids so they do not re-infest new plantings the next season. Old plantings of tomatoes, peppers and other host crops should be removed from the garden at the end of the year and composted or placed in the trash. Psyllids reproduce faster as temperatures rise and their population peaks in late summer. Planting tomatoes, peppers and eggplants as soon as spring weather is warm enough may allow the crop to mature before psyllids attack them. Floating row cover cloth like reemay can help protect young plants. Place the protective cloth over newly planted seed or transplants – especially when planting in summer – and keep young plants covered as long as possible.
Check tomato plants weekly for signs or symptoms of tomato psyllids. You may be able to control a light infestation if plants are treated early. Most pest control products used in home gardens have not been evaluated for psyllid control, but some information is available.
Many gardeners prefer to use organic products. Ultra fine oil (Safer Sun Spray and similar products) provide relatively good control of the psyllid in greenhouse studies according to Dr. Trumble, but insecticidal soap is not as effective. Sprays containing an extract of neem oil (Greenlight Neem Concentrate) help control a variety of garden pests and may also work on tomato psyllid. Oils and soaps kill pests on contact so you must spray all plant surfaces including the undersides of leaves to control psyllid. Applications of sulfur dust also help deter psyllids, but sulfur may harm tomatoes if oil is applied later.
Broad sprectrum insecticides like malathion will kill tomato psyllids, but frequent use also harms beneficial insects and this may allow other pests like spider mites and leaf miners to build up. The insecticide carbaryl (Sevin) should not be used to control psyllids because it can cause the pest population to increase.
A few beneficial insects as well as spiders, birds and other natural enemies feed on psyllids, but they do not provide enough control to protect tomatoes during a psyllid outbreak. A relatively small number of psyllids can damage tomato plants and cause severe crop loss before beneficial insects control the pest. Protection of natural enemies is still important however; since they control a wide variety of garden pests.

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