Milkweed (Asclepias curassavica) leaf disease?

Colima, Mexico(Zone 11)

Several of the leaves on all three of my Asclepias curassavica plants are turning yellow, getting black marks, then turning brown and eventually falling off. Has any one had this problem? Or know what might be causing it? I recently had 3 generations of Monarchs that have now moved on and now the Queens are coming to lay eggs and i am concerned about the leaves. I still have plenty of green leaves to support a few generations of Queens but would really like to solve this leaf problem.

Any suggestions or shared experiences would be much appreciated. I suspect it may be due to over-watering although the plants do have excellent drainage and are in good soil. Thank you.

Thumbnail by vitrsna
Prairieville, LA(Zone 9a)

As a general rule, Asclepias is a pretty much disease free plant. The info below is all I could find regarding yellowing leaves and brown spots. Although, the brown spots may be some form of insect damage.

Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH (alkaline soil). Or the nutrients may not be absorbed due to injured roots or poor root growth.

The Asclepias genus usually does not require a great deal of water, but if the soil is not draining well, the roots will be inhibited from picking up the trace elements in the soil, especially iron, and that will result in the plants becoming chlorotic. The major cause of chlorosis is a deficiency of one of the essential micronutrients such as iron or manganese. This deficiency occurs not because the nutrients are lacking in the soil but because they are unavailable due to a high-pH soil. At these higher soil pH levels (6.5 and above) many trees and shrubs are incapable of taking up adequate amounts of iron or manganese. This part of Central Texas has a lot of alkaline soil; however, some compost mixed into the soil or used as a top dressing often will address the problem, providing better drainage, reducing the alkalinity and improving the texture of the soil and permitting access to the trace elements needed.

Colima, Mexico(Zone 11)

Thanks Moon...I don't have a mechanism for measuring the pH of the soil. I know there are kits to buy...but not here. These plants are in containers now with good soil mixed with gravel to provide good drainage. Last year when the plants were in the ground, I also had the yellowing leaf/brown spots problem which is why i have moved them to pots this year because i thought they were not properly draining. They are not the same plants though...i started new ones from seed. I have mulched them well with dried, crushed leaves.

They were in full sun which is a lot for any plant at this close distance from the "full sun" means toast. I have moved them to locations with less severe sun and they are not getting so droopy by noon. When they get droopy I give them water which is not such a good idea probably but i have caterpillar eggs on them now and think these little pillars coming up are not going to be too happy with droopy leaves to eat.

I'm pretty sure the roots are not damaged or compacted. The soil comes from oak forests...perhaps oak is alkaline...i will look that up, also there are some pine needles in the mix. Maybe they would appreciate some well composted sheep pooh around the peripheries of the pots. Good grief, this is a weed here, growing out of concrete, etc., of course these plants are not as luscious as my pampered ones. So i will experiment a bit and search a few things.

I also posted this at the butterfly and hummingbird forum and have not received any replies so i am thinking perhaps i'm the only one who has experienced this problem...don't have any of those chubby yellow aphids least not at present. I would say that 90% of the plants appear luscious and healthy and i haven't noticed any suspicious bugs lurking around them.

Assuming the soil might have a high pH, do you think sheep pooh might be a good counterbalance?

Thanks so much for the info Moon,

Prairieville, LA(Zone 9a)

Oh you are most welcome. You mention gravel....if the gravel is crushed limestone, it would help create an Alkaline soil. A gentle way to help create more acidic soil is with plain white vinegar. You use a very dilute mix of 2 TableSpoons of vinegar to 1 gal of water.. or Epsom salts,( 1 TableSpoon per gal.) also help. This adds magnesium and sulfate to the soil which will help the plant absorb nutrients and iron better.

Here is some info on natural acidifiers. (manure is one of them)

Reading various links, they all state that while the plant grows in "sandy disturbed soil", it thrives in fertile, amended soil...add some sheep manure and peat most to your soil mix and repotting the plants in that would help...just make sure not to use fresh manure as it can burn. Also read that it can take part shade, so make sure the container is large enough and place them where they get full morning sun, but some light shade from 1PM to 5 PM.

Hope this helps some...
Buena Suerte!

Colima, Mexico(Zone 11)

why, ms. moon you are the cat's pijamas! this is the first time i actually took notes from a reply. because i have 3 large plants in separate pots, i will try a little experimenting. one plant with white vinegar/water mix only, one plant with vinegar + manure and peat moss worked into the existing soil, and one plant with manure and peat moss worked into the soil without the vinegar. it will be interesting to track the results.

I think the pots are now well relocated to avoid too much sun.

i can't repot the plants just yet and not for a few months because i do not want to disturb the butterfly eggs, the tiny caterpillars, etc and there will probably be at least 3 or 4 successive generations before the plants are exhausted. from egg to eclosure (we are talking about Queen Monarchs) is about 28 days (not long enough for the plant to create significant new growth) and while some of the caterpillars are quite large and almost ready to pupate, new eggs will be oviposited on the plants and tiny new caterpillars will appear.

so i will give this a try, take a look at the website you sent, and also look for ways to determine if the soil has a pH that is too high without having a commercial kit. i think there must be ways to do this...i hope it does not include eating dirt :-0 much appreciated...always there is so much to learn.

Prairieville, LA(Zone 9a)

Meow!...Grin I am fairly familiar with the process...I grow A curassavica and A tuberosa just for our Monarchs here. I did find this link on how to do your own Ph test with out a kit. I think everything should be readily available to you there. might try using a "slurry" rather than disturbing the plants...just make up the three mixes you mentioned above and add them to water in a container with a lid...(sort of like compost tea) then shake the dickens out of them til fairly well mixed and water the plant. What solids are left can be gently distributed around the surface and will be absorbed in the next few waterings. That way you won't damage any roots in the process.


Colima, Mexico(Zone 11)

perfect! i suspected there must be a way and started searching last night when an interruption took me up and out and in another direction entirely. this is very exciting (and so easy) and i can't wait to try it! also i was thinking just how i would go about the manure, vinegar, and peat moss applications..."slurry" is the best idea, of course. thank you for thinking of it for me. saludos calidos, beverly

Prairieville, LA(Zone 9a)

Glad to help Beverly...sometimes it takes a more than a village....GRIN

Abrazos para ti, mi amiga (and that pretty much finishes my remembered Spanish from 1965)lol


Colima, Mexico(Zone 11)

yes it does take more than a helps a lot if some of the people in the village are brilliant and DG has quite a few, including your own self (seems like you know a lot about monkeys too). i wrote to admin a while back (melody) and suggested that with over 650,000 participants, we could be our own country but i don't think there has been any movement on that idea. perhaps it is under consideration :-D

this looks like a great forum so i'll be tracking it from now on. i read some prior posts and am going to try an ant/aphid trap that was suggested in january. i might even have something to offer here.

Prairieville, LA(Zone 9a)

Thanks Beverly, but I research better than I remember....grin

This is a very helpful forum....and if I am lucky I learn a little every time I check in here.

I reckon that this would be the Principality D'Gardenacea, a global community....grin

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