Here's what it looked like a few days ago. I hope I don't have to dig up the rose bush next to it. I've never seen a plant look like its been rolled around in flour before. Shame it had to be the first cosmos seed I've ever sown.

why does it have to go.. for a little PM? .. if in fact that is what it is???/

if it dies.. it dies.. but what.. you cant wait..

if PM .. i really cant tell from this pic.. baking soda and water works..

i really dont know what a fungicide would do for a mildew.. but its been years since i read a label .. or used the stuff .. i personally dont care about mildew.. i think of it as variegation.. lol ...

do you spray the roses for PM??? do they now have PM ... something doesnt seem right here ... in fact.. the last time i sprayed for PM .. was 20 years ago.. when i was into roses.. maybe it is a fungicide thing.. lol .. full circle there ... but is it on the roses???

ken

Gardentantrum, that absolutely looks like a case of powdery mildew, a pathogenic fungi that can affect many different kinds of plants. Your cosmos is one of the more susceptible plants.

I'd be very tempted to pull up the cosmos at this point, rather than begin a chemical treatment. Though, if you should decide to go that route, there are many commonly available fungicides labeled for the prevention and cure of PM. Just read the label.

It's not likely that your rose will need to be removed. The fungal strain which affects cosmos is not the same one for roses. However, if the environmental conditions are right, the rose PM could be triggered.

PM thrives in high humidity, but can be rinsed off the foliage with a spray of water.....as long as the foliage hasn't become seriously infected. Applications of horticultural oil, in particular Neem oil, are a very effective preventative.

For now, I would simply remove and dispose of the cosmos. The fungal spores are persistant, so no composting. I'd also avoid planting anything in that same plant family for quite some time.

PM is one of those diseases that I believe is largely preventable with careful plant choices and good garden housekeeping practices. Left unattended on a tender plant, it infects the cells and can kill plant tissue.

i havent fooled with cosmos in 30 years ..

and i am now thinking.. this was why i gave up on them ...

the simple solution.. is to accept that their season is over.. and remove them .. and be done with them ...

there are a lot of options available .. that would be carefree.. for a much longer season ...

who knew there were two version of PM.. one might expect 2 names.. for two different things.. go figure.. lol ..

ken

Ken, there are many, many different species of powdery mildew. The organism that infects cosmos won't affect grapes, or azaleas, or lawns, or squash, and on and on.

rhizo_1 - I figured digging it up is better than spraying coz it is so huge of a plant. It was about 5ft tall and now it's shriveled down and powdery. I'll plant cosmos again in a different spot next spring and be more vigilant next time. The roses seem unaffected by the mildew, which I'm happy about. Thank you for your response :)

Ken - I had a hard time letting go coz it's my first cosmos from seed haha, I've been so patient with it. I'd like to try the plant again in the future, but maybe not during the rainy season. It was the only plant that didn't look good/better after the rain.

I would consider spraying the rest of the garden. But I feel you on the fact it was you're first cosmo. It was very pretty! Also I would check your soil drainage. Cosmos work well in dry soils. Add some peat or perlite the next time you plant in that spot.

ladyrose65 - the only plant around it are rosebushes, I sprayed them thoroughly today, hopefully they stay unaffected. Will I be able to plant, say, lamb's ear and not have it turn out the same way? Is it in the soil now and I have to dig it all up? Sorry, I've never dealt with such a sick plant before haha I'm nervous about that spot now. I have clay soil I amended with compost, I'll dig it up and mix perlite in since I do have some lying around. Thank you :)

first ... get over the guilt/unhappiness ..

every flower has its season .. and sometimes that season is not long.. you wouldnt complain.. that a tulip only blooms for a week.. would you???

so be happy for your success .. and move on ... crimminey.. you grew them from an embryo ... aka .. a seed ...

second.. it has NOTHING TO DO WITH THE SPOT .. meaning the soil ... see PS ...... its a cultural problem.. most mildews.. occur and thrive during hot, humid NIGHTS [perhaps they are the vampires of the garden] ... my PM does anyway ... and i will yell.. IT HAS NOTHING TO DO WITH THE SOIL .... CULTURE is how the plant is treated above ground .. as in heat.. sun.. humid nights.. etc ... though the spores.. if that is the right term.. can be on the soil surface i suppose .... but once disturbed.. that should not be an issue ... and probably solved simply with a mulch ... [and rhiz can correct me again.. if i am wrong.. lol] ...

amending planting holes.. ONLY .. can lead to problems.. you really should NOT throw things ONLY in holes.. just because you have it laying around ...

a little perlite.. is NOT going to change the drainage capacity of a clay soil ... especially not a hole dug into a poor soil ...

BTW .. if you are growing.. and succeeding with rose.. what i consider one of the most foo.. of the foo foo ... you really shouldnt be all wrapped up in problems with cosmos ... you really are.. much further ahead.. than you consider yourself ...

ken

ps: i said it has nothing to do with the spot.. but one thing that reduces it.. is night air movement.. when things are too jammed together.. and air movement is restricted.. that culture.. can make a problem explode.. PM is endemic in monarda also ... it was a nightmare for me way back.. so i dug it up and set it in full sun ... by itself.. and the problem was reduced significantly .. and the biggest thing.. culture again.. was that i learned not to come home from work.. and in the late evening.. give everything a shower with the hose.. if your plants go into dark.. DRY!!! ... again.. you reduce the 'potential' greatly ... darn.. the PS is getting longer than the reply.. lol ... reducing potential.. would be part of IPM .. integrated pest management.. and should be next on your learning curve.. so as to reduce the need to run to the chemical bin.. and getting out the sprayer.. every time something is not perfect ... [PM is not a pest.. per se .. but it would be within the concept of such.. wouldnt it???]

PPS: .. if i were to be thinking of spraying the roses.. i would have cut the cosmos to the first or second buds.. down near 6 inches.. and then sprayed those with the the roses.. and with severe canopy reduction.. removal of the PM.. and an intact mature root system.. they probably would have been back to 3 feet in weeks ... it would have been a neat experiment ... and would have increased your learning curve.. had you not had the chicken little complex of utter destruction ... based on fear .. there is a mixed metaphor for you .. lol