Aster yellows

Candidatus Phytoplasma asteris

also called yellows

Yellowed, stunted plants whose flowers turn eerily green, leafy, and sterile; spread by leafhoppers and there is no cure.

Phytoplasma No cure Spread by insects Spreads to neighbors

What you'll see

Flowers turn green and leafy instead of coloring up, and set no seed.
Foliage yellows while the veins may stay green.
Growth is stunted, bunched, and witches-broom-like with many spindly shoots.
Stems can be distorted and one-sided.
The whole plant takes on a stiff, deformed, sickly look.

Why it happens

Aster yellows is caused by a phytoplasma, a bacterium-like organism that lives in the plant’s sap channels. It is injected as leafhoppers feed, and the insects carry it from infected weeds and perennials to healthy plants across a wide host range.

It builds in warm summers when leafhoppers are active and abundant, especially near grassy margins and weedy ground where they breed.

Treating it

There is no cure; lift and bin or burn affected plants so they cannot be a source for leafhoppers.
Do not compost the material.
Clear infected weeds nearby, as they act as a reservoir.
Reduce leafhopper numbers to slow further spread.

Keeping it away

Keep down weeds such as dandelion and plantain that harbor the phytoplasma.
Discourage leafhoppers, using fine mesh over vulnerable crops if needed.
Inspect plants and remove any with greened, leafy flowers promptly.
Avoid planting susceptible ornamentals beside rough grassy ground.

Who gets it

Asters, chrysanthemums, coneflowers, marigolds, and many daisy-family flowers, along with carrot and lettuce.