It could be milkweed yellows. Yellow coloring of leaves and the bunching and stunting of new growth are symptoms of this problem but not exclusive to it. Other piercing insects can have that same effect on your plants by disrupting the natural growth of the newest most tender leaves as can other diseases and even lawn "weed and feed" preparations that stray into the garden bed. There are other milkweed yellows symptoms that are more differentiating but not present here, like extreme distortions of stem, flower and leaf growth.

Milkweed yellows is spread by insects and the safe advice is to remove any plants with even a suspicion of the problem as soon as possible to reduce the chance of spread to healthy plants. You can have tissue from the removed plants tested by the plant diagnostic lab at Cornell Cooperative Extension of Westchester County so you know what is going on if you start to see similar markings on your other plants.

Hi Ilana,

You caught them in the act! These insects may be causing this damage on their own by sucking the juices from the leaves - or - they may be bringing milkweed yellows to your plants. You can keep the plants and take the risk of losing the others if it is milkweed yellows, or remove them. Either way you lose some plants and you will need to strike a balance that feels comfortable to you.

I am not certain about how extensively the milkweed yellows phytoplasma distributes itself in the plant. The disease may affect the entire plant down to the roots and I would be concerned about planting more milkweed in a spot where some root fragments may still be in place.

The garden is a place of insects and safely deterring them is difficult. For small flying insect like these (maybe aphids, it's hard to see), spraying leaves, top and bottom with a hose to knock them off every morning can be reasonably effective.

Best,

Leslie

NYBG Plant Information Service