another pic

Probably powdery mildew. To late in the year to spray.
Best management for now is to discard the leaves as they fall.

Also, get the tree into the ground.

Looks like powdery mildew to me as well. BTW, although some people refer to this as a poplar, it isn't. Liriodendron are actually in the magnolia family.

Thank you for the replies. What caused the mildew and how can I prevent it on its new leaves in the spring? I grew one a few years ago and it did not have it. it was in a pot for about 2.5 years before put in the ground.

hot warm nights...

its a mildew.. surely you know where mildew grows.. in the dark .. in dank humid windless areas ...

insure the plant goes into darkness dry .. no after dinner wetting ...

increase air movement if possible .... by removing surrounding plants ...

and.. its a tree... plant it in the ground ... trees are extremely hard.. to grow in pots ...

it may never happen again ... there is no cure ... in a given season ...

it can be prevented with simply baking soda and water.. i am sure you can google that ...

i have a dozen of them ... NEVER had this problem.. so.. i suspect.. its something you are doing ...

full fall cleanup.. get rid of the leaves.. and i might even wash down the pot with that baking soda stuff.. to remove any potential overwintering spores.. and i wouldnt even research it.. because i have it laying around.. and its basically free.. harmless.. and would take about a minute... shorter than firing up the computer ....

ken

You're growing tulip poplars from seed -- nice! That powdery mildew won't hurt anything. The little thing is about to go dormant anyway. And once you get it in the ground and it matures, chances are the PM won't be a problem.

Liriodendron tulipifera -- that's your tree, and one of my favorite latin names. I think it's far too nice to just be called a "poplar".

Yep, powdery mildew and Liriodendron is fairly susceptible to tbis disease if the conditions are right. It tends to show up when temperatures begin to cool down, but the air is still humid. Warm days and cool nights are perfect for PM.

This fungus does not need sitting water on the leaves in order to germinate, contrary to what many people believe....just humidity. As a matter of fact, spraying the foliage with plain water can be the simplest control, if caught early enough. Water kills PM spores. That's all I've ever used, as long as I spot it soon enough.

At this time, don't worry about it; your tree is about to lose its leaves for the winter. I would absolutely treat the bare twigs with horticultural oil in the spring...just before the swollen buds begin to break.

The potting medium must be one that is very porous, fast draining. Woody plants do best when grown in a bark based mix. The typical houseplant medium is not the best option for a woody plant.

The location should be sunny and in an area of good air circulation. Avoid excess fertilization.

There are many good options for prevention......plain water sprays, insecticidal soap, and neem are great preventative solutions. Some people recommend milk sprays or baking soda but be sure to research the mixing rates. Should you not be able to keep it rinsed away and infection occurs, Neem oil can cure a mild infection.

Lots and lots of good information about this disease on line. Do some reading and you'll feel more confidant. It's not a mildew, per se, but a true fungal disorder. In ground trees can get it, too, if the conditions are right.

PM spores travel in the wind. Check around to see if there are any other infected tulip poplars around just out of curiosity.

Thanks everybody for all the replies and ideas.

In the ground and looking good!

I'd have to wonder about the advisability of planting a tree that wants to grow in excess of 60' tall and with a spread of more than 30' that close to a house!! Seems not well thought out.

The City of Beverly Hills has hundreds of these trees, and they all are planted around 10' from the structures and they seem to be doing OK as you can see. The do trim them every few years. The only issue is the seeds/leaves in the gutters.