Aster Yellows

Pull the whole plant, roots and all, if the flowers went green and leafy and the new growth is yellow or stunted, because aster yellows is already in the sap from the crown to the bloom and a spray will not take it back out. Bag the plant or bury it under soil so leafhoppers cannot keep feeding while the crown is still green. If only the cone grew tufts and the leaves still look like themselves, that is likely mites, so clip those heads and leave the clump.

Gardeners often call this a virus. It is a phytoplasma, a tiny bacterium without a cell wall, moved by the aster leafhopper when it feeds. It does not live in soil, and it does not jump from leaf to leaf on your hands the way some mosaic viruses do. Cutting the weird flowers off a coneflower does not cure the crown. See leafhoppers if you need to name the wedge that hopped. The job here is the diseased plant.

Pull the whole plant. A spray will not rewind it

Once the phytoplasma is in the phloem, every part of the plant is infectious, so clipping a green bloom, spraying the foliage, or waiting for a heat wave will not rewind the crown. Dig the coneflower, aster, marigold, or zinnia including the roots, because hoppers can still feed on a leftover stub. Do the same for a carrot with a hairy bitter taproot or a lettuce head that stayed pale and twisted in the heart. The plant may not drop dead overnight, and some perennials can sit there stunted for a season, which is exactly why you pull them instead of hoping they outgrow it.

The phytoplasma dies with the plant. It does not persist in soil the way a wilt fungus can, so the hole is not poisoned. What matters is that hoppers cannot keep sipping green tissue, so bag the plant for household trash or bury it fully under compost or soil. Do not leave it on top of the pile, because a crown that still looks alive can infect the next insect that lands. Once the tissue is dead, the organism is gone. Wash the shovel before you divide a healthy clump, not because the disease lives on dry steel, but because a still-green crown on the blade is still a live host.

After the pull, walk the weedy edge. Dandelion, plantain, thistle, and Queen Anne's lace can hold the phytoplasma from one year to the next even when they look almost normal, so those plants are reservoirs, not a side project. On carrot, lettuce, and celery, a floating row cover from emergence keeps hoppers off the first leaves, which is prevention for next year's row, not a cure for the plant you already pulled. Fogging a flower bed to kill every hopper will not uninfect a coneflower, and landscape sprays are a poor match for an insect that arrives on spring winds. If you need to confirm the wedge itself, that is the leafhopper job, not this one.

1. Walk the whole plant before you dig. Green leafy flowers plus yellow or stunted new growth is yellows. Tufts only on the cone, with foliage still the right green, is likely mites, so keep the clump and clip those heads.
2. Dig the plant, roots and crown included, on coneflower, aster, marigold, zinnia, carrot, or lettuce that already shows the whole-plant pattern. Bag the tissue or bury it under soil so hoppers cannot feed while it is still green.
3. Pull nearby weedy hosts that can overwinter the pathogen, especially dandelion, plantain, thistle, and wild carrot, then watch the rest of the bed for the next odd bloom.
4. Cover next year's carrot or lettuce at emergence if hoppers have been a problem, and skip a canopy fog as a rewind. A bottle does not take phytoplasma out of sap that is already infected.

Green spoons plus yellow leaves is the tell

The usual backyard picture is a purple coneflower whose petals turned into a ring of tiny greenish-yellow spoons around a deformed cone, or tufts of small green leaves growing where the flower should have been. That leafy bloom is phyllody, and it comes with the rest of the plant looking wrong: new leaves yellow while the veins stay greener, stems stiff and upright at narrow angles, and often a witches'-broom of thin shoots from one point. A plant infected early stays small. Flowers may never take their proper color, and they often set no seed.

Vegetables tell the same story in different clothes. Carrot tops go yellow, then bronze or reddish-purple, and bunch into a short witches'-broom, while the taproot stays skinny and puts out lines of hairy extra roots that taste bitter. Lettuce inner leaves curl and twist, the heart stays pale, and outer leaves may show pink or tan spots and fail to head. Onion leaves come twisted, yellow, and too many. None of those crops catch this from a neighbor's leaf rubbing them. A hopper has to feed.

Symptoms can take ten to forty days after the feeding, so a bed that looked fine in June can go strange in July. Cool, wet stretches favor spread. A long run of heat above about 88°F can quiet the organism in both the insect and the plant, which is why a hot week sometimes makes a sick coneflower look a little less awful, but the plant is still infected and still worth pulling. You do not need a lab to pull a ruined annual. A clinic test is leftover honesty if you are protecting a named perennial and the mite fork is not clear.

If only the cone is tufted, keep the clump

Coneflower rosette mites live inside the developing flower and make fuzzy knots or green-to-reddish tufts on the cone, but they do not yellow the whole plant or turn the petals into a ring of green spoons. The foliage stays the size and color it should be, so you clip and bag the deformed heads instead of digging the crown. There is no mite slug on this site yet, and a horticultural oil next spring before bud break is leftover mite advice, not a yellows cure. If you already pulled a clump that only had cone tufts and healthy leaves, that was the mite fork, not a failed yellows pull.

Herbicide drift can twist leaves on several species in the same week after a lawn spray, which yellows almost never does in a single afternoon across unrelated plants. Mosaic viruses leave a light-and-dark patchwork on the leaf without turning a coneflower into leafy green spoons; see mosaic viruses for that quilt, and do not paste an aphid soap ladder onto this disease. Hungry plants go evenly pale and still make flowers in the right color. A hopper that only stippled a leaf, with no twist and no green bloom, is feeding damage on the leafhopper page, not a reason to rip the bed.

Related reading

• Leafhoppers — the wedge that moves this phytoplasma; hopperburn and covers stay on that page.
• Mosaic viruses — patchwork mottling without leafy green blooms; a spray will not rewind those either.