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I have (3) tomato plants that have been showing white residue on the foliage - see photos below. One plant in particular has this consistently. The residue can be wiped off with a moist towel.

I suspected this might be some type of mildew and have sprayed with a diluted neem oil. This hasn't seemed to clear it up. I would love to resolve this issue before it gets worse/seems to negatively impact the plants. I am using the same potting mix/nutrients on the (3) affected plants as I am two others which aren't showing any signs of this issue (seedlings sourced from different nurseries). I have been watering in the AM 1-2x/week at the soil level.

Please let me know your diagnosis and recommended treatment. Thanks!

I'm not familiar at all with this type of phenomenon. The strikingly white substance looks more to me like something had dried on the leaves, I'm thinking something like airborne pollen settling on dew on the leaves, moisture hanging at the ends of the leaves, then evaporating to dry with the "residue" remaining on the leaf tips.

In my area, I might see something like this that are YELLOW from the massive pine tree pollen in the air.

Hmmm... "Bay Area" -- could this possibly be due to salt in the air? -- same explanation as above?

What is this substance like -- cottony? Crystalline? Does it dissolve in water?

I agree! It does look like something dried on the leaves. But it is SO white - and I am used to seeing pollen be yellow. Although a quick searched (which brought me to bee-keeping forums, ha) showed that there are white pollens as well. I have star jasmine flowers on my porch... but it is not seen on all plants! There are two much larger tomatoes which are closer to the jasmine and they have none of this. I'm not close enough to the bay to get much salt air, but thank you for considering all factors.

The substance is more crystalline I suppose (I'm posting more close up photos). It does dissolve in water! Today I am also seeing some spotted yellowing on the leaves.

I'm not sure if this is due to my neem oil treatment (well diluted in water, sprayed yesterday morning on the foliage) - OR if this is related to the white deposits - OR something additional plaguing this poor plant? Hopefully the additional photos help...

I assumed on mine it was just too much fertilizer.
The spots actually fluoresce under black light,which looks cool.
I just planted them anyway and will see how they do.

The way the white spots are located on the leaves it looks like residue of some kind that has dried there. Have you been doing anything other than neem oil? Any fertilizers? Epsom salts? That would be my guess, something that has been air sprayed which has dried on the plants.

xtgold wrote:I assumed on mine it was just too much fertilizer.
The spots actually fluoresce under black light,which looks cool.
I just planted them anyway and will see how they do.

Interesting that you used a black light to inspect them!

KitchenGardener wrote:The way the white spots are located on the leaves it looks like residue of some kind that has dried there. Have you been doing anything other than neem oil? Any fertilizers? Epsom salts? That would be my guess, something that has been air sprayed which has dried on the plants.

I absolutely agree - it does appear as though something is dried on the leaves. However it is strange since only certain plants are showing this.. which you'd think if it was something in the air it would be on the leaves of other plants (or at least all the tomatoes). Nothing else on the foliage. I used the neem oil only after this started. Fertilizer used is only a seaweed/fish fertilizer mixed into the water. No salts. Let me know if anyone has any other ideas! The yellow spots are making me a bit more suspicious...

cruisin_psu wrote:
Interesting that you used a black light to inspect them!

I had the black light on the plants 24 hours a day as an experiment.Grow lights were on a timer.
I also hit them with a couple of 20 year old strobe lights for a couple of weeks.
I was using a spray fertilizer, but the spots only appeared at the tips of the leaves.

OK.. so the plant is looking better today. Still some white marks, but way less. The yellowing has not spread (fingers crossed) - still not sure what was going on with this thing. Hopefully I don't need to borrow xtgold's stobe and black lights.. not sure what my neighbors would think of that

I'm going to go with salt deposits from unknown sources (??) unless further evidence presents itself.

Pics from today:

Looks like some healthy tomato plants you have there!