Tomato query

[ken]

Daughter has raised a query about her tomatoes which I can't answer. She says that on some leaves, which she has now removed, she found a number of yellow spots on the top surface, each with a whitish lump on the reverse. On each of the affected leaves there were about 15 spots/lumps. Sounds as if it might be a tiny pest rather than a virus or fungus, but I really don't know.

[ken]

[img]tomato%20query.jpeg[/img]

I now have a pic which, if the upload works, may provide a clue...

[ken]

Better luck this time?

Tomato query.jpg (163.75 KiB) Viewed 5260 times

[Geoff]

My first thought is Red Spider but I haven't so far found a photo to confirm it.

[Johnboy]

Hi Ken,
Suspect that the plants are suffering from Tomato Leaf Mould.

http://gardener.wikia.com/wiki/Tomato_leaf_mould

The way to treat this disease is explained on the above website.

JB.

[ken]

Thanks, Geoff and Johnboy. I'm not sure about it being tomato leaf mould - the description I've seen says that the undersides of the leaves would have brown felty areas which coalesce to fill and kill the leaf, and that doesn't fit with daughter's photograph. Red spider mite sounds more likely, particularly when I read (Terry Marshall's book, Tomatoes[i][/i] ) that the mites can be red, brown or greyish green in colour. I've tried enlarging the pic to the maximum, but can't make out the individual mites. Anyway, I'm very grateful to you both. I'll pass on your comments.

[John Walker]

Ken, it's good news - this isn't a pest or a disease, but a physiological disorder called oedema. It happens in cool weather when humidity is high and the soil/compost is moist. The leaves can't lose water (by transpiration) fast enough, so the cells burst and rupture, which leads to the 'blisters' on the underside of the leaves, and the corresponding marks on the top.

It doesn't usually do any harm, and there's no 'cure' as such, apart from easing up on the watering and making sure there's plenty of ventilation, even on cool and overcast days. Other plants suffer too, such as fleshy-leaved geraniums.

There's a bit more info and a picture here: http://plant-disease.ippc.orst.edu/show ... cordID=969

and the RHS website has info too (although the image at this link isn't oedema): http://apps.rhs.org.uk/advicesearch/pro ... px?pid=391

And if you Google 'tomato oedema' and hit 'images', it'll show you lots of other examples...

[ken]

That's very helpful, John, and a great relief. Not a disorder I've come across before, but very believable in this odd summer we're having.

[Johnboy]

Hi Ken,
I take it that the photo you posted shows the underside of the leaf on the LHS and the top of the leaf on the RHS. I sincerely hope that John Walker is correct but I have my doubts.
Time is the revealer of all so time will eventually tell us.
JB.

[John Walker]

Ken, please be in no doubt that this is indeed oedema on your daughter's tomatoes. I've seen it for myself on and off during many years of gardening. The lumps matching the spots is unmistakeable. But I took the liberty of sending your photo to the Royal Horticultural Society (RHS) Members' Advisory Service, and they confirm it's oedema (the reply was from their chief horticultural advisor):

"This appears to be consistent with oedema and is probably a consequence of more water around the roots than can be shed by the leaves."

They also supplied another link to the RHS website, which has some more general information on oedema: http://apps.rhs.org.uk/advicesearch/pro ... px?pid=637

Fingers crossed for some dry days with plenty of sunshine...

[ken]

Many thanks. I'll just add that my daughter has since told me that the only variety affected is Latah. For those who don't know it, this is a bush variety, very early fruiting. It has much skinnier leaves than more typical tomatoes, putting all its energy into flowering and fruiting. I think it is a great variety, but the fact that it has skinny leaves may well mean it has more difficulty coping with excess water and would tie in with the oedema diagnosis.