Cucumber plants - yellow splodges on leaves. Can anyone please help identify?

Morning all

I've only grown cucumbers once or twice in the past and that was many years ago, so they're all a bit new to me. I was wondering if anyone could be so kind as to help identify what might be wrong please? I've tried searching for myself but there seem so many possibilities.

Photos below. And here's some relevant info and possibly a big clue too!

- I don't know the variety. Not even sure if they are climbers or danglers, or whether that even matters in terms of how I let them grow? I did get two from one person and two from another, so not likely to all be the same.

- They are growing in large pots in a polytunnel.

- They were doing really well until a few days ago when I noticed two leaves had what looked liked powdery mildew.

- Having read up on powdery mildew last year, I convinced myself that prevention is better than cure. I just hadn't got round to it yet! So spurred on by this, I removed the two leaves and gave the rest of them a spray of Potassium Bicarbonate (with a little washing up liquid).

- I did so in the morning as it was forecast to be cloudy for the day. However, it turned out to be sunny for quite a few hours after I gave them the spray.

So could it be leaf scorch from the wet leaves/sun? Too much Potassium Bicarbonate in the mix? The washing up liquid? Or is that all a red herring and could it be something else entirely?

Many thanks,
Max

 

Doesn't look like powdery mildew to me - it's the wrong colour.
Possibly snail or slug damage.

 

It looks as if a small slug or snail has had a little munch on the leaves. Have you put any slug pellets around the plants, if you use them?

 

Thank you all so much for replying so quickly, I really appreciate it

Sorry, perhaps I wasn't the clearest in my original post. There were only two leaves with what I think was PM, and I removed them before doing the potas. bicarb. treatment, and before taking the photos. So PM was just part of the storyline and not something I suspected nor what i tried to show in the photos. I grow a lot of squashes so PM is something I'm quite familiar with.

That's great to hear. I must admit, that's what my money was on to begin with. It was only when I googled "yellow spots/lodges...." that I started reading about kinds of potential diseases and got a bit worried. Ultimately, the timing seemed to good to be unrelated to the spray. There wasn't a hint of yellowness or owt else before I sprayed them. But then you never know!

We're in South West Wales and it's usually an absolute slug fest here. Luckily so far we've had little damage from them. I've had loads of strawberries and not one has had a single nibble (albeit they're in pots off the ground in the poly). Nor have all my small squash plants. I've got off very lightly, although it's still relatively early season and I expect there are legions waiting in the wings. I wouldn't rule out the damage being from slugs, but I don't think they're my prime suspect at the moment.

As for slug pellets... I don't use anything at the moment. Perhaps it sounds daft, but I don't like killing anything unless I really have to. Maybe one day the time will come when enough is enough. Until then I'll carry on with nocturnal slug checks!

Thanks again

 

My concern would be the liquid detergent. See COSHH leaflet for ingredients. I have concerns for the potential of incorrect dilution rates, even for household use, where subsequent rinsing is often minimal.
https://www.hertsfullstop.co.uk/CoshhDataSheet?i=70411730
It is not a substitute for soft soap for horticultural use. I presume you considered it a wetting agent.

 

Fair point @infradig ... To be quite honest, I think the only reason I used it is because I had a memory of using it last year (which was the first year in which I used the potas. bicarb). Perhaps I should have looked into it a bit more but tbh I was in a rush.

We use BioD washing up liquid (fragrance free). It says it is "100% naturally derived", and that it has "environmentally responsible ingredients". Mind you, it does have warnings about skin irritation, what to do if you get it in your eyes, etc. So maybe even if it is better than the non-eco alternatives, I should be more hesitant next time. Here's the ingredients for reference. I guess citric acid is probably not good for starters! However, I did only use two squirts in 5L of water...

Above 30% Anionic Surfactant. Below 5%: Amphoteric Surfactant, Sodium Chloride, Citric Acid. pH 11.5.

Many thanks

PS - I guess I've also read it is used for other things like aphid control, which made me feel more comfortable using it. But less is certainly more, so if not needed in the potassium bicarbonate mix, I'm happy for it to go!

 

To use a detergent as a wetting agent needs only 3-4 drops of detergent in about 5L water, so it's extremely diluted.
I use a tiny amount of shower gel instead, but not one with moisturising stuff added.

 

Powdery mildew is mostly down to growing conditions IMO.
Stagnant air and plants on the dry side at the roots, often at the end of the season.

I just spray with diluted milk without detergent.

 

Sodium chloride.
This would damage cucumber in even weak concentrations, be alright on brassicae however !https://www.vegetables.bayer.com/gb...ides/cucurbit/cucurbit-plant-salt-injury.html

 

Many thanks for all the replies and sorry for my delayed response.

Lesson learnt and thanks for the explanations. You know, thinking back I might have used shower gel last year when using PB for the first time, not washing up liquid. So probably my memory at fault here... The plants haven't died yet so hopefully the mistake wasn't too drastic.

I was planning to spray them periodically over the growing season as I've read that prevention is better than cure when it comes to powdery mildew. So next time I spray, should I use just Potassium Bicarbonate or add a little shower gel? We use Faith In Nature - Grapefruit and Orange in case that makes a difference.

And one last thing, should it be a very light spray or get the leaves nice and wet?

Thanks again