Why is My Echinacea Turning Green?

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First the disease affects echinacea’s cone, causing green growth to appear. Photo: pamsenglishcottagegarden.blogspot.com

Yes, there are a few plants with green flowers: green roses, green zinnias, green glads, green echinaceas, etc. These plants are hybrids developed for their unusual color. But if a plant you choose for flowers of another color suddenly starts producing green flowers, the chances are pretty good it is suffering from a disease: aster yellows.

Aster yellows is a very common in the wild, found especially in goldenrods, asters and other wildflowers, and is caused by the aster yellow phytoplasma (AYP), a bizarre entity closely related to bacteria, but behaving like a virus. Notably, once a plant is infected, no treatment can cure it. 

Leafhoppers transport aster yellows from one plant to another. Photo: http://www.gardeners.com

Aster yellows are transmitted by leafhoppers: by piercing plant tissues, they inject the phytoplasma which then extends gradually throughout the plant, affecting its growth and gradually weakening it.

Over time, the entire flower turns green and often begins to produce satellite flowers. Photo: http://www.missouribotanicalgarden.org

The first symptom in many plants is the greening of the flowers. This is called phyllody, the abnormal development of floral parts into leafy structures. In the case of echinaceas, a kind of green growth starts to form on the cone in the flower’s center. Over time, the cone produces small satellite flowers that are completely green. Weird … and really not too wonderful!

The only treatment for aster yellows is to destroy the plant. If left alive, the disease will gradually spread to neighboring plants, including echinaceas, asters, carrots, cosmos, strawberries, daisies, marigolds, zinnias. More than 300 other plants in 84 different plant families are known to be infected by this disease.

This is a case where a quick strike solves a ton of future problems: yank the infected plant out at the first sign of symptoms and you can prevent the disease from spreading to your other garden plants.

Article originally published on September 27, 2014. 

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What are Those Weird Green Flowers?

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This echinacea flowers is heavily infested with aster yellows.

Are you finding flowers in your garden that are strangely colored or deformed? With petals that are green or greenish, short or even absent, or there are leaflike growths instead of normal petals? Sometimes small green secondary flowers pop out of the main one, like little green sputniks orbiting a green sun. Is this a mutation?

Probably not. What you’re seeing is most likely aster yellows, a disease caused by a phytoplasma called aster yellows phytoplasma (AYP), a microorganism similar to a bacteria. It causes various forms of abnormal growth, including phyllody (when petals are transformed into leaves) and floral virescence (when a flower turns green), but also chlorosis (yellowing of the foliage), flower sterility, stunted growth, or even witches brooms (dense, massed growth).

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Normal echinacea flowers turning green under the influence of aster yellows. http://www.extension.umn.edu

You’re more likely to see the aster yellows on plants in the daisy family (Asteraceae), including echinaceas, gaillardias, asters, marigolds, rudbeckias, and coreopsis, but it also infests onions, carrots, snapdragons, and celery, all of which are from other families. In fact, the disease has been found in more than 300 species in 38 families of flowering plants.

Aster yellows does not kill its host plant, but certainly reduces its productivity and makes it less attractive.

The Cause

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Aster leafhopper.

Aster yellows is transmitted by the aster leafhopper (Macrosteles quadrilineatus), a small sucking insect common in fields and gardens throughout much of the world. When it pierces the leaves or stems of a plant in order to suck up its sap, it injects, if it is contaminated, a few phytoplasma cells which then reproduce and spread throughout the plant via its sap, causing the changes noted. If a phytoplasma-free leafhopper then bites into the plant, it can pick up the disease and carry it to a new host.

What to Do?

Ideally, you need to discourage leafhoppers from ever reaching your plants.

There are certain ways to do this. For example, avoid applying too much nitrogen-rich fertilizer (the first number on the fertilizer label indicates the percentage of nitrogen), as leafhoppers prefer the tender green growth that results from excess nitrogen applications.

Also, leafhoppers seem to dislike mulch, so adding mulch may help.

Encourage beneficial animals in your garden, too. Spiders are particularly effective, and studies show that leafhoppers tend to avoid plants where they see a spider web.

Finally, some sources claim pelargoniums and petunias will repel leafhoppers. I’ve never had much luck using supposedly repellant plants (and indeed, petunias are among the many plants can suffer from aster yellows!), but who knows? This might be the exception!

Another method of treatment is using pesticides to control leafhoppers early in their cycle, before the damage is done, thus nipping the infestation in the bud. But leafhoppers are pretty discrete insects, largely hiding among foliage where they can rarely be seen. Thus they may already be present in large numbers before you even notice them.

Even when you have an insecticide on hand, leafhoppers can be hard to reach. They are very alert little pests and will jump or fly out of harm’s way given the slightest chance. Among the products you could try that should be relatively effective are neem (no longer available in Canada), insecticidal soap and pyrethrum. Remember though that by spraying your entire garden with an insecticide to prevent leafhoppers, which is pretty much what you’d have to do, you’ll be killing beneficial insects too. If you do go this route, at least make sure to apply the insecticide early in the morning before pollinating insects are active.

That said, not many gardeners are proactive when it comes to preventing leafhoppers. Usually they run into symptoms of the disease rather than the insect that transports it, far too late for insecticides. What to do then?

The Ultimate Solution

Essentially the only treatment for aster yellows that is totally effective is to remove and destroy the diseased plant. There is no known cure for aster yellows. An infested plant will often live for several years and remain a source of disease that each year’s new generation of leafhoppers can spread to plants nearby.

Culling a favorite plant deformed by aster yellows can be painful, but it will do your other plants a world of good. And the sooner you do it, the safer your other plants will be.20160610A

Laidback Gardener Tip of the Day

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No Pity for Green Flowers!

septembre 27Yes, there are a few plants with green flowers: green roses, green zinnias, green glads, green echinaceas, etc. These plants are hybrids developed for their unusual color. But if a plant you choose for flowers of another color suddenly starts producing green flowers, the chances are pretty good it is suffering from a disease: aster yellows.

Aster yellows is a very common in the wild, found especially in goldenrods, asters and other wildflowers, and is caused by a phytoplasma (formerly it was called a mycoplasma), a bizarre entity closely related to bacteria, but behaving like a virus. Notably, once a plant is infested, no treatment can cure it.

Aster yellows is transmitted by leafhoppers: by piercing plant tissues, they inject the phytoplasma which then extends gradually throughout the plant, affecting its growth and gradually weakening it, but the first symptom is usually the greening of the flowers. This is called phyllody, the abnormal development of floral parts into leafy structures. In the case of echinaceas, a kind of green growth starts to form on the cone in the flower’s center . Over time, the cone produces small satellite flowers that are completely green. Weird… and really not too wonderful!

The only treatment for aster yellows is to destroy the plant. If left alive, the disease will gradually gain the neighboring plants, including echinaceas, asters, cosmos, strawberries, daisies, marigolds, zinnias and more than 300 other plants.

This is a case where a quick strike solves a ton of future problems: yank the infected plant out at the first sign of symptoms and you can prevent the disease from spreading to your other garden plants.