My six tomato plants started out looking great when I planted them in mid-May. This week the foliage color of all them looks pale - new growth at tops of plants (leaves) look smaller, and some leaves are curling.

Last year I had a problem with one or two plants that I diagnosed (who knows if correctly) as cucumber mosaic virus. I pulled one of them up and the other survived and produced though the plant was never all that vigorous.

What can I do to correct this?