what is your media ... and is it balanced

looks very high peat... could the pH be out of whack????

stop spraying until you ID a problem to solve ... even if using an organic ...

and how deep is your pot"???

is the plant in full sun???

bottom leaves falling off.. is somewhat norm to a cuke .... so if its growing with vigor from the top ... i wouldnt be too concerned ... though of course.. it indicates something ...

and tell us when you sprayed the oil ... that should never be in sun ....

ken

Hey Ken,

The medium is a homemade "mel's mix". It's 1/3 Peat, 1/3 Vermiculite and 1/3 homemade compost. Havent tested the PH for this batch but its normally around 6.5 - 7.

The pot is 1ft deep and they're not actually in the sun. They're outside on the patio in the shade but have a 50w Grow Led on top of them since they're in the shade.

New leaves have those yellowing edges, they just seem to get more necrotic on the bottom ones and then there are those spots or lesions. :: Any thoughts?

That leaf damage could be a watering issue. Might be staying too wet below the surface, have you checked for that? I would have used perlite instead of vermiculite in that mix.

tj

That appears to be a nutrient deficiency, not insect damage. Have you done a soil test for nutrients and soil pH? What leads you to believe that that soils "normal" pH is 6.5 to 7.0, a good reliable test or a home garden soil test kit that is not very reliable?
Spraying any pesticide, unless the pest has been identified, is never a good idea.

Kimmsr - Seems you were spot on. I had done a home kit soil test. Perhaps that was not the most accurate. I let things sit for a couple of days and here's what the cucumber looks like now. Pretty clear its a nutrition deficiency - just not sure if it's potassium, magnesium or something else. Any idea?

Thanks for helping out all...

It can be difficult to guess since many factors enter into nutrient deficiencies. Soil pH, too much of one nutrient can interfere with a plants ability to use another nutrient, or the soil just may not have what the plant needs.
Perhaps the linked article might be of some help.

Here is a link that might be useful: nutrient deficiencies

Agree. The root cause can be tricky. Just wondering - looking at the leaf which deficiency is it symptomic of? Is this a Potassium deficiency? The yellowing areas between the veins are starting to exhibit the same burnt color as the edges (copper brown color) and its moving up.

I'm finding a lab to do the soil test for me but wondering what i can do in the meantime. I've tried to do multiple soil tests with 2 kits and they come back saying the PH is highly alkaline. Could it be this high soil PH thats locking out nutrients? The soil is a combination of 1/3 compost blend (vermicompost, home made compost and neem cake), 1/3 vermiculite and 1/3 peat moss.

Wondering what to do in the interim until i can get the soil tested to prevent the cucumber from dying. Looks like its on that path anyway so i'd rather do something than nothing.

All the best,