yellow spots on crab apple

I have some one year crab apple seedlings. Some have developed yellow spots on the leaf. See picture. I would appreciate ideas on what is the cause. Thanks

Frank

Look up Cedar Apple Rust.

Thanks Jim.

I did look it up. Do you know any effective treatment? Or should I just pull the seedlings and move on....

Thanks

Frank

I use "Daconil." You can buy it just about everywhere in The States.

You also have to deal with the alternate host. Are there red cedars near your bonsai collection?
Of course in deciding whether they are worth the trouble, you have to remember:
Crabapple seedlings will not bloom until they are about ten years old. You may be able to hasten this process a little by growing them in the ground.
If they are seedlings you have no way of knowing whether they will bloom well or little, or what the flowers will look like.
You will have much more consistent results if you take cuttings or air layers from the parent tree.
Also, it is too late to spray when you see the rust spots. You start spraying in the spring as soon as the tree starts to leaf out. By now the spraying season is almost over. Also use a dormant spray next winter.
Iris

Outlaw thanks. I have Daconil. WHat schedule of spraying do you use?

bonsaisr yes I have some red cedar nearby. The seedling pictured is in the ground in a bed with some maple and one pine. I realize it is years away from achieving bonsai status. Thanks for the tip on air layering,

Frank

I buy Daconil in concentrate. It is a much better buy this way. I have a small orchard and spray all my trees once a month till summer, bonsai and none bonsai. I know that when it is cool and wet I can and will have problems. I start spraying the orchard and grapes when the buds start breaking and always have some left over so I hit all the bonsai at this time also. I suffer from apple cedar rust, black spot, anthracnose, and pine needle cast otherwise. Maybe I spray too much, but I sleep better at night and when I am spraying have none of those problems.