Hi Dotty - how many plants are we talking about covering?

There are many sheet plastic greenhouse-type plans and kits on the market. They range from just tall enough to cover 3' tall plants to big enough to grow a small tree in.;) I have linked a couple of sites below.

And you can learn a great deal about more options and growing under cover over on the Greenhouse & Garden Structures Forum.

I don't know that a dome type cover will help with preventing blight - in it's various forms ("blight" is kind of a catch-all label) the fungi/bacteria that cause it are present in the air and soil - but a cover can raise temps somewhat and with proper air circulation you can control the humidity a little.

Tomato Production with High Tunnels

Hoop Houses

Hoop House Construction

Hope this helps. ;)

Dave

Thanks Dave. This is needed just for a couple of plants -- but they are very large -- 30 inches high but sprawling over a very big area, likely 5 feet by 10 feet. I know I shouldn't have let them grow like this but it is too late now!

Dotty, you need to be careful whenever you cover any plants with plastic. You can kill them in just one morning of sunshine if there is no ventilation under the plastic cover. A spun polyester row cover would be more suitable but I don't know of any studies demonstrating a blight reducing effect. The opposite may actually occur due to reduced air circulation around your plants.

Dave has provided some good references but PVC hoop houses may be a big disapointment in northern climates since the PVC becomes brittle and breaks easily in freezing temperatures.

My advise would be to establish a preference of what you want to accomplish. If season extension is your goal then a row cover will buy you time beyond a few light frosts. If you are trying to ward off diseases than you need to identify the disease, access the risk and act accoprdingly. Don't fire bullets into the air hoping to solve the problem.

I'm a strong advocate of high tunnels since this year all of my tomatoes are grown in them . However, they require an extra amount of planning. Plan this year for next year's crop under plastic. You may be better off with a low cost alternative remedy for this year's crop.

bmoser thanks. I'm sure that it would be very difficult to do anything with this year's sprawling crop. I promise to do things differently next year! I am getting a few ripe ones from other smaller plants that are water deprived so at least that is good. Perhaps later in September the green ones will ripen. We have had an awful summer with not many hot days and a lot of cloud cover so I can't expect too much. Thanks again.