Friday, July 2, 2010

Tomato-potato psyllids watch

Psyllids are insidious insects that cause a plant condition known as psyllid yellows, the result of a toxic saliva injected by the insect. Be on the lookout for these insects on your tomatoes and potatoes now.

Insects are reported to be heavy in the Arkansas Valley and adults have been found in sweep nets in Fort Collins. Psyllids do not overwinter in Colorado and migrate from overwintering sites in southern TX, AZ and NM. Reports from the southern part of the state are tip offs to be on the watch for them. Outbreaks are erratic depending on winds and weather conditions. They can also be transported on transplants.

Watch for the eggs and nymphs. Eggs are small (one-thirty second inch), orange-yellow and supported by small stalks. Beneficial lacewings have similar eggs but are larger, white and on longer stalks. Psyllid eggs take 6 to 10 days to hatch into nymphs.

The nymphs look like flat plastic discs attached to the backs of leaves or on stems (photo above right). They are yellow at first but become green and well camouflaged as they mature. The nymphs don’t move once they settle down to suck plant juices. They excrete small, waxy beads of white “psyllid sugar” (photo left) as they feed for 2 to 3 weeks.

The adults are rarely seen and are green at first but rapidly turn dark Adults fly to new plants to lay eggs and 4 to 7 generations are produced in a growing season.

Symptoms on potato and tomato plants are similar. Yellowing or purpling along leaf midribs and leaf edges is concentrated in top leaves. As the disease progresses, the yellow-green or purple-red color spreads to the entire top growth and growth slows. New top leaves often remain small and tend to stand upright giving the top an almost feathery appearance.

When psyllids attack tomato plants early, effects can be so severe that little fruit is set. Infestations later in the growing season on larger plants cause only a small yield loss. If psyllids attack potatoes before tuber set, many small tubers form. Later attacks reduce growth and cause irregularly-shaped potatoes that may sprout prematurely underground before harvest.

Because insects are small and don’t attract attention due to being stationary and camouflaged, they go unnoticed before the damage is well underway. Watch on a regular schedule for psyllid sugar and turn leaves over to look for nymph “discs” (photo right). If found, take action right away.

Do all you can (fertilize and water regularly) to get plants growing vigorously early. Insecticides labeled and available to homeowners are permethrin and esfenvalerate products. An alternative is sulfur dust if leaf undersides can be coated. Two percent insecticidal soaps provide useful if more erratic control.

Psyllids infest but cause insignificant damage to other vegetables in this same family, eggplant and peppers.

Photo credit: All photos Whitney Cranshaw, Colorado State University entomologist


  1. Psyllids are in Englewood, CO on tomato plants. How often would the plant need to be sprayed? In other words, would another migrating population be a concern later in the season? Is the tomato plant "cured" of psyllid yellows once the plant is sprayed and presumably the insects are gone? Will the tomato plant then resume a healthy cycle of setting fruit and producing good tasting tomatoes? Basically, I'm wondering the likelihood of getting a good tomato crop following control of psyllids. Thanks!

  2. Thanks for the update on your Englewood garden! There is no cure once insects have injected toxic saliva into the plants. It's really a matter of dose - how much saliva is injected into what size plant. If you have large plants as I've been urging people to have by fertilizing to obtain size early, your chances of getting a harvest are better.

    Spraying to kill psyllids before they inject too much saliva minimizes the amount. Between the two (large sized plant and minimal saliva) you can likely obtain some harvest. One or two sprays 10 days apart to kill this bunch of insects is probably sufficient.

    Keep in mind that other psyllids can fly in to lay eggs and you may discover a new infestation in future weeks. This sets off another round of decisionmaking about whether to spray or not. As I said, this is an insidious insect.

    I was in Fort Collins last Friday and saw potatoes already very yellow from psyllids. It looks like a serious year for this insect on the Front Range.

  3. In our Centennial community garden we have psyllids on 10 of our very large tomato plants. They are flowering and fruiting normally but on the lower portion of the plant, the leaves are covered with these aphid like creatures. I am really not sure what to do to control them. I am concerned about using soap and oil sprays for what they might do to beneficial insects.

    How do you determine the best course of action?

    Additionally there are eggplant and peppers in adjacent but separate raised bed gardens. There do not appear to be any issues at the moment.From what I have read, it seems the only prevention is maintaining healthy plants.

  4. Lady beetles, green lacewings, pollinating bees and most other beneficial insects are not very susceptible to soap sprays. Hope that helps with your decision.

  5. We had them and we sprayed the undersides of the tomato leaves with a solution of water and dishsoap. It appeared to do the trick.

    Carl, I cannot find my contact info for you. Can you contact me? James Bertini of Denver Urban Homesteading

  6. Thank you James and Carl.
    What dilution ratio did you use water:dish soap?What dish soap did you use?
    With the rain that we are receiving how does that influence promulgation of psyllids?

    If I spray with soap and it rains does that eliminate my efforts or is the damage done to the insect on contact?

  7. I'm a plant biologist at the University of California, Davis. There has been some research that sulfur volatiles can repel the psyllid. Plants emitting these volatiles might help as a preventative method. For instance, garlic, and mustard seed plants.

  8. Sulfur dusts and lime sulfur were the first treatments identified to control psyllid. They still work. However, I don't think that even sulfur dust, which I still find on some garden center shelves, lists tomatoes and potatoes on the label.

    The blog idea likely is speculation based on the activity of sulfur. It would probably be an interesting study to attempt, but it is unproven as a control as best I am aware. - Whitney Cranshaw, Colorado State University Extension Entomologist

    If the Anonymous person who commented has studies that show results, Dr. Cranshaw and I will be interested in reading them. Let us know. - Carl Wilson

  9. SOAP SPRAYS - For Nanrfull who wrote questions about the use of soap sprays, the latest info on the use of soaps and detergents for instect control is in our CSU Extension fact sheet at It includes concentrations if you want to mix your own instead of purchasing insecticidal soaps from a garden center. Soaps are essentially a contact insecticide with short residual as you will see in the fact sheet.

  10. They got my tomato plants in Denver pretty bad this year. Still going to get plenty of harvest since they are all 6ft+ tall, but they're definitely going downhill. Tried insecticidal soaps, dishsoap sprays, and it seems to slow them down but not much. Hope they don't come next year, but at least I'll know what to look for earlier now.