The main foliage disease we see in the UK is blight - phytopthera infestans, caused by high humidity and temperature. A couple of days rain, with temperatures over 15C creates the perfect conditions for the fungal spores to sporulate (?). It does take 48 hours of consistent moisture on the foliage so it is possible to do a preventative copper spray if the prevailing conditions are right for blight to take hold. Used to be called a 'Smith Period' but is now called something else...and in the UK, it used to be possible to subscribe to 'blightwatch' which was localised warnings when entering into a 'Smith period'. Once infected, there is really no cure as the disease moves systemically through the whole plant.

I have no knowledge of conditions pertaining to the US but think, at the very least, I would use a mix of copper sulphate and hydrated lime (Calx) at a ratio of 1;1;10 (copper, calcium hydroxide, water). Used to be known as 'Bordeaux mix'.

The older, lower leaves do start to look a bit dodgy by around now so I whip them off, so it could just be age. Blight is pretty recognisable, causing blackened patches on the stems and leaves...and eventually the fruits.

Removing the lower leaves helps to ripen the lower trusses too.

When it comes to fungicides, whether copper or other, be aware that most fungicides are preventative, not curative. That is, you apply them BEFORE the fungal infection can develop. Once you have a developed fungal infection, most fungicides won't do a lot of good. There are curative fungicides, but I believe they are expensive, and not available for residential use. So this is a lesson that pertains to next year. The best weapon against fungal infection is crop rotation. The fungal spores are soil-borne. That's why, without crop rotation, you'll fight the same ones every year.

Looks like a fungal disease.

FWIW, the fungus lives in the soil, tomato plants shpuld not be planted in the same area for consecutive years. Rotate your crops or give up on tomatoes in that bed for a few years.

Yes, once something like blight gets going, there is nothing to do...but there is a 48 hour window where you can nip it in the bud as it were.

I think there is quite an interesting range of responses regarding crop rotations.. I certainly started out with quite fixed principles of crop rotation but I don't beat myself up if I only manage a 2 year rotation or get some of the 'rules' a bit mixed up. Alan Chadwick, of Chadwick cherry fame kept a permanent tomato bed and I know it is fairly common practice (for some people) to keep permanent onion beds too. Rose replant syndrome has always been a part of rose culture in the UK but less so in the US. and really controversially, I think Charles Dowding (No-Dig gardening) has had an experimental long term potato bed. It's interesting (to me) how gardening practices are a bit of a mish-mash of science (empirical evidence based) and social/cultural/anthropological customs. How that line moves around and practices change over time. I don't think I would be anything like as prescriptive as I used to be...not least because I have lived through quite a few absolute certainties turning out to be quite shaky...

I do rotate.

Better keep rotating!

Some disease/fungus can overwinter in the soil or on dead plant matter, while some need living plant tissue to survive. Most are also airborne and brought in on the wind though so even if you move a plant 100 feet from where it was in years prior it can still get infected just the same. You can mitigate the risk of disease by trying to increase air circulation (via pruning or spacing plants further apart), keeping the soil mulched, growing disease resistant varieties, etc. but if disease is a common occurance regardless of these cultural practices then it may be best to use fungicides proactively before the first signs of infection.

Rodney

I have grown no end of 'blight resistant' tomatoes...but really, I don't think such a thing exists. I have managed to save some of the crop by chopping off the affected foliage and you can cut the tops off potatoes.. Have you had a coupla days of persistent rain, mxk3? If it is blight, the foliage must be really wet for a full 48 hours for the spores to literally swim around extending hyphae into the plants cellular structure. Without this much moisture, I wouldn't be too worried just yet.

Either early blight or septoria leaf spot and are both fungal diseases which are very common. They both do about the same thing and both are treated the same so it really doesn't matter which on it is. I just cut off a bunch on my indeterminate plants today, all had fungus except for my Mountain Magic, this cultivar is bullet proof.

Early blight and septoria leaf spot information and pictures. shows how to tell the difference between the two. I won't spray unless it gets out of control, but there is a point where it will causing a total loss, and had this before until I learned how to deal with it. Now it's an inconvenience.

My indeterminate tomatoes are in two different locations one I rotate but the other spot has been used for over a decade with limited outbreaks. How I limit outbreaks using the same spot every year is using Woven landscape fabric underneath, using drip irrigation, thinning out vegetation within the center of the plant so air can circulate, and removing every speck of plant debris including the root ball, and the woven fabric makes it easy to sweep up all the plant debris at end of season. I only remove lower leaves if they are yellowing or signs of disease. I do get aggressive thinning out the branches on the inside cutting off most branches growing inward. There are enough leaves growing outward to easily support tomato production.

My determinate plants do get rotated, woven fabric, drip irrigation, and fall clean up but are not pruned or thinned of any vegetation. The plants are 2 feet apart and a thick wall of vegetation covered with 20 to 30 pounds of tomatoes each, and if a fungus hits earlier than when I believe I'll get the full harvest then they get sprayed. No problems yet for this season but if I do spray I will continue every week alternating between fungicides.

Something to mention, Late blight is a water mold and not common, but effects are devastating and what caused the potato famine in Ireland in the mid 1800's. People use terms early and late blight as if they are the same thing all but they're two different pathogens. With late blight the plants are consumed quickly and can look as if they were hit by a frost. Late blight outbreaks are tracked and mapped every year so farmers will know if it's in their area. Last year there were small outbreaks in CA, FL, TN, SC, and MI. covering a just a few counties each. This year the only reported and mapped outbreak seams to be an little north of Toronto. I think I had it once over 25 years ago and it was devastating and the plants were dead in a week. So it's septoria leaf spot or early blight but IS NOT late blight.

FWI, Removing the lower leaves helps to ripen the lower trusses is a myth sorry to say. If the leaves are green they're actively photosynthesizing and producing sugars to support plant growth. With this said there is no harm removing them but It would be wise to wait until the plants have grown to the point those lower branches wouldn't be missed or there will be a short delay in growth. When plants are young I'll only cut off anything that touches the ground, and when they're big only if they yellow or diseased. (see last post)

yep, late blight is definitely a bit 'game over' in my neck of the woods. Despite the wet summer, have avoided it so far but I do keep my spray at the ready.

For the first time in my life, I have been utterly idle and left all the indeterminate tomatoes to do their own thing - no pinching, tying or faffing (I have my greenhouse back-ups though). I am honestly wondering why I have stressed myself to mental breakdown, rabidly nipping tying and mucking around. Although the plants are all a bit out of control, I can't see that the crop is going to be much diminished by idleness.

I generally chop the leaves off when they are beyond the pale - wrinkled, yellow and skanky...but I am not any sort of expert tomato grower. If it wasn't for the offspring bleating about passata and such, I would happily abandon these, almost the last of the vegetables I bother to grow anymore. And as for potatoes. I say never again every year...but I am both northern and half irish so ya know...life without spuds... not to be borne

Late blight is common in the UK. Very. Last year there was none...but not much of a crop either cos it was so dry

But does anyone know exactly what it is?

Seriously?

WE all know what it is! We all told you what it is and I even left you a link that tells you EXACTLY what it is. Did you click the link and did you read the information? It's not hard to learn and understand.

Looks like septoria leaf spot to me. My tomato plants get it every year after Michigan summer’s torrential rains, and this summer has been wetter than usual…I simply can’t keep up with leaf removal, although I certainly am trying. My tomato plants have no leaves at the bottom at this point!

I also do crop rotation, but only among three different beds. Next year, in addition to removing lower branches, I’m going to put a thick layer of straw over the soil so there isn’t any backsplash onto the tomato plants from the ”diseased” soil when it rains hard.