What is wrong with my asclepias?
Hi - the lower leaves on my asclepias syriaca are turning yellow. Some get black dots before they fall off the plant. I practice good hygiene and remove the fallen leaves and whenever possible pull them off the plants even before they drop. Last summer i had the same issue and it eventually impacted the entire planting, which is huge. It is in a mixed perennial bed with dozens of other species of native plants. In addition to impacting plants as it moves across the beds the problem eventually impacts leaves higher and higher on the plant until all leaves on the (sometimes seven foot tall) stem are destroyed. There is no obvious insect damage. My garden is all organic since the milkweed is there for the monarchs and we host hundreds of caterpillars each year.
We think this is not related to an insect or disease but abiotic.
How deep is the mulch? They are tough plants that doesn't have a heavy mulch in nature.
Also, it looks like your gutters drain there. Have you checked how wet the soil is there? Make sure that it drains well, or maybe consider extending the drainspout to the lawn or an area where plants who like wet feed grow- there is a native swamp milkweed.
The spots on the leaves are just the natural senescence or breakdown of dying leaves.
Hi Christine - Thank you for your message. There may have been some accidental false flags at play here. These beds dont receive anything but rainwater (I showed that one spot only because two plants of different sizes displayed the same problem) - the gutter visible there drains across the front walk and down the driveway/into the lawn. The mulch is about .5" to 1" deep with last fall's (unchopped) leaves from our oak and maple trees underneath. I did write before about sour mulch but that was actually on behalf of my parents. I haven't had a problem with sour mulch before. I used bagged shredded hardwood and it has been down for about six weeks with no smell or visible burning of any the plant species like what I saw at my parents' house. I have included a few more pics that hopefully give a better sense of the nature of the beds. Since they are nearly all native plants they are planted pretty close together. Thanks for any further ideas you can share, I really appreciate it!
The milkweeds in your new photos look very healthy. We still think this is just senescence of the older leaves. Lower leaves that do not receive enough sunlight will yellow and drop out. Too much/too little moisture can cause yellowing. Nitrogen deficiency can also cause yellowing in lower leaves, but overall, your plants look healthy. We wouldn't recommend a fertilizer application.
There might be something unsuitable about the soil. Milkweeds are typically from prairie (grassland) areas -- they don't normally grow in soil that receives mulch of oak/maple leaves and hardwood mulch. Furthermore, because these are wild plants, little is known about the diseases of milkweeds. (See the Milkweed FAQs from Xerces Society, https://xerces.org/milkweed-faq/#8.)