What are these spots on a young cucumber?

[elk4baby]

I have a young cucumber seedling/plant. It's ready to go to its position in the garden now, but I'm really concerned about the damaged leaf. Is this infectious? What should I do to make sure the other leaves remain healthy?

Here are the photos:
https://s1288.photobucket.com/user/elk4baby/slideshow/

Just to confirm, I can't see any insects or anything else, the plant has been grown indoors from seed. Other plants from the same seed packet seem to be doing just fine, the plant pictured is the only one that seems to be affected.

(very amateur gardener, obviously )

[evtubbergh]

It is hard to see but I would guess a fungus. Use a copper solution or a mixture of 1 part milk to 3 parts water. Spray only until just moist all over and repeat weekly or after rain. Destroy leaves that are infected if you can remove them without killing the plant as the treatment does not cure the fungus but prevents it from spreading. Destroying the spores is the most effective way.

Just a tip for photographs; make sure the little rectangle in the view finder is on the piece you want in focus and depress the button half way. You can then move the view finder around before depressing all the way to take the photo. If you use a touch screen phone (works on iPhone) tap the area you want in focus and when it is ready take the photo.

[elk4baby]

Thanks for the photo tips, I couldn't quite get it to focus properly. I have now added a couple more photos, hopefully they are a little clearer (the first photos, same link).

The patches seem to be dual-coloured (if that makes any sense). They're darker-than-the-leaf green with light almost-cream in the middle. Not to the touch, but they do look a different texture too - the spots look like they're a bit thinner than the rest of the leaf.

I have a systemic fungicide that I use on my orchids - Westland Plant Rescue - will it work on the cucumber?
I also have Bordeaux Mixture - would this be better?
If neither is suitable, what would you advise I use to treat this?

[hendi_alex]

I would say snip the leaf off and forget about it, unless the problem seems to be moving to other leaves. It is about time to move the plant outside, and those improved growing conditions will likely take care of any issues. The plants look very tender, so be sure to gradually introduce them to sun, wind, and hard rain.

[elk4baby]

I am planning to move it to a large pot covered with a greenhouse-type cloche. It should do fine in a pot, as it's the Spacemaster variety. And the cloche will have it sheltered from the wind and any hard rain.

[imafan26]

It looks like cersospora or some other fungal disease. Fungal diseases are easier to prevent than cure and the spores can survive to cause problems another day. I myself would cut my losses and bag the plant and start over. It might be a good idea to make sure you do not wet the leaves and you take preventive measures if the conditions for fungal growth are ideal.

https://www.seattleurbanfarmco.com/2013/ ... ay-recipe/