Pest or disease on tomatillo leaves

[cowshill]

Can anyone identify and give me any advice on what is attacking my tomatillo plants? Pictures below. The tomatillos are being grown in a small greenhouse in grow bags. The problem begins as a few small dots and slight yellowing on the leaves and fairly quickly progresses to the stage shown in the photos. Although diseased leaves are picked off the plants, new leaves are continually becoming affected. The overall vigour of the plants does not appear to be suffering at this stage. There are 4 tomatillo plants in the greenhouse and all are affected. At this point no other plants seem to affected - the greenhouse population includes tomatoes, peppers, cucumbers, strawberries, herbs and various vegetable seedlings in trays. Thank you for any assistance you can offer.
- Cowshill

[Geoff]

I get this on them every year and, as you say, it doesn't seem to bother them much. Although I have never found any culprits I think it is the plants reaction to aphids or something similar. I rarely spray anything but one year when it was particularly bad I did use a white fly spray on them and it seemed to help. It is less of a problem outside so I now grow them only outside, they are tougher than they look.

[FelixLeiter]

It's a virus. It is transmitted through the seeds, so don't attempt to save any seeds from your plants for next year. Picking off leaves does not prevent the spread of the virus through the plant. You may yet get a good crop, depending on how your plants progress. Any stress, though, and they may quickly succumb. With that in mind I am not optimistic about their prospects in grow bags. They do grow better outside than in a greenhouse, which can be too stuffy for them, so their prospects may improve if you move them outdoors. Copious quantities of water is what they really enjoy. Is this the purple- or the green-fruited type? I find that the purple tomatillos are that little bit delicate (but are better eating).

[cowshill]

Thanks for the input. Unfortunately, growing them outdoors is not an option, as I am in an exposed location high in the north Pennines where the wind would quickly rip them to shreds no matter how well they were tied in. They are the green variety. Also this is the third year I have grown them from seeds out of the same original seed packet. All four plants have the disease this year, but I had not seen it on any plants the previous two years.
- Cowshill

[Geoff]

I stand corrected but I guess like many plant viruses it can be aphid transmitted so that would be why I achieved some control.

[Johnboy]

Hi Felix,
Have you any more information regarding the virus? You say that is bourne in the seed which interests me greatly. This is purely a question for self information.
JB.

[John Walker]

This is not a virus disease but a growing disorder called oedema.

It is not controlled by spraying but by improving your growing techniques: the cause is too much water at the roots (i.e. overwatering) and too high humidity around the leaves (i.e. a need for more generous ventilation). It affects different plants grown under cover.

In a nutshell excess water in the leaf cells causes them to swell up and 'blister'. Some die, which leads to the dead-looking areas/holes which could be mistaken for actual virus/disease symptoms. It is not a problem carried by seeds.

"Oedema, often spelled 'edema', is a physiological disorder that develops when a plant absorbs water faster than it can be lost normally from leaf surfaces. The term itself means 'swelling', which describes its initial stages. Excess moisture builds up in the plant and causes swellings that appear initially as pale-green or water-soaked blisters or bumps, primarily on the undersides of leaves. Although oedema mars the beauty of plants it rarely kills them."
Source: http://www.extension.umn.edu/projects/y ... edema.html

There's some more information and a near-identical picture to the one posted by cowshill, here:

http://plant-disease.ippc.orst.edu/imag ... cordID=969

And also here. NB this is a PDF file - oedema is on page 15:

http://www.ces.ncsu.edu/depts/hort/gree ... hysiol.pdf

Existing damage can't be undone. Try reducing watering (especially in these current weather conditions!) and ventilating as much as possible - especially on dull, humid and overcast days.

[cowshill]

Thanks, John! Your info seems to hit the nail on the head. I'll try to water more judiciously, but getting the right amount of water into growbags has always been the most problematical part of using them. Last year I let them get too dry a few times, and I think this cut into my crop. I just need to find the happy median.
- Cowshill

[cowshill]

P.S. I also sent the photos to the RHS, and they have now replied confirming the oedema diagnosis.
- cowshill