Yellow spots/patches on courgette and squash leaves.

[colonel]

Hi there,

I have quite a few courgette and squash plants which are mainly growing well. However, one squash plant and one courgette have patches of bright yellow on one leaf per plant!

I have checked the underside of the leaves and there is no sign of mildew. Could it be downy mildew or something else? A deficiency perhaps?

I have also noticed one or two other plants that have just one tiny yellow spot on one leaf.

As I said, all plants seem to be growing well so any advice about these mystery yellow patches is appreciated, just to make sure.

The photos I took wouldn't upload too so no images, sorry.

Thanks guys.

Stay safe and happy growing

[ameno]

If the courgettes are yellow, or if the squash is a yellow patty-pan type, then that's fairly normal. They just get yellow leaves sometimes.

If they are not, however, then it probably is a sign of something less welcome. It won't be mildew, though. If the yellowing is on the young leaves then it's probably a nutrient deficiency (iron, most likely, or possibly sulphur or manganese).
If the yellowing is on older leaves, or on both old and young leaves, especially if the yellowing is mottled or patchy, then it is probably a viral infection. Cucumber mosaic virus is the most likely, but there are others.

[Jungle Jane]

Sometimes the oldest leaf at the bottom goes a bit yellow as it feeds some of it’s nutrients to the newer growth,do they need potting on or have you got any fertiliser?

[colonel]

Thanks for the replies. The yellowing is mottled/patchy but is only on one leaf on each plant and yes it is on an older leaf?

Any ideas on how to treat?

Thanks again

[colonel]

Have give fertiliser and also recently potted on

[colonel]

Have give fertiliser and also recently potted on

[Jungle Jane]

It’s difficult with no photos,I think it seems like a normal thing,same with tomatoes,it shouldn’t spread to the new growth. How big is the plant,how big is the pot & what fertiliser used (when was it given. Are you watering carefully not to get the stems wet incase of stem rot,that’s the worst problem) I don’t remove the yellow/green leaf it’s still being used by the new growth,unless it’s completely yellow.