Hello, My calendula flower stems keep getting these small black bugs that I cannot get rid of. What causes it and how can I avoid them? Are the seeds stil good to be gathered even though they sometimes are full of bugs? Also, what causes the milkweed plants to get the small, reddish bug infestation on their stems? Thank you.
I will answer the milkweed part of your question first as the answer is more obvious to me. The orange bugs are aphids, Aphis nerii. They suck the plant sap and while a few are no problem, a large number will cause the plant to suffer. The best ways to remove them are to squish them between your fingers and brush them off or hit them with a stream of water from a hose. You will have to support each stem so it doesn’t break. It is possible to add rubbing alcohol or insecticidal soap to the water but these additives will kill beneficial insects, such as lady bugs, syrphid flies and wasps, that eat the aphids and will also kill monarch eggs and larvae. From personal experience, I find that Swamp milkweed Asclepias incarnata attracts a lot more aphids than Common milkweed A. syriaca or Butterfly milkweed A. tuberosa. This link will give you more information on aphids on milkweed.
With regard to the calendula flowers, you didn’t say enough about the black bugs for me to be able to say what they are. They could be black aphids, so similar in size and shape to the orange aphids on the milkweed. They could be garden fleahoppers, Microtechnites bractatus. These are small black insects, approx 2 mm long; they hop when disturbed, which aphids don’t, they also suck sap and they leave whitish or yellowish speckling on the leaves. They could also be thrips, Leptothrips species. They are up to 3 mm in length, but there don’t seem to be solid black thrips – they are either black with white bands or black with white wings. Maybe you could send in a picture. Regardless of what they are, treatment is the same as above – squishing with fingers and brushing off or hitting the plant with a stream of water. You will be able to harvest the seeds as these insects are sucking the plant sap and are not damaging the seeds.
Here is a link with more information on growing calendula: