I have a tiny backyard in Cabbagetown, Toronto, almost totally turned over to raising vegetables in raised beds. For years my spinach, beets and swiss chard have been destroyed by this (see below) What is it and what should I do?
Beets, spinach and Swiss chard are the main vegetables in the Amaranthaceae family (formely Chenopodiaceae family). The main difference is the edible portion of the plants – roots vs. stems.
Generally plants in the same family, like spinach, beets and swiss chard, have the same nutritional needs and the same pests & diseases.
If you grow beets exactly where you planted them the year before, leaf spot may develop. Grow beets in a different location each year.
All vegetables need the complete range of soil nutrients, both the big three –nitrogen, phosphorus and potassium- and the minor nutrients. However, different crops use them at different rates. If you grow the same crop in the same patch of soil for several years, it will deplete some of the nutrients essential to that plant and the yields will decrease. In addition, pest and diseases, that attack that particular plant, will build up in the soil and the crop will be under stress & constant attack. This problem can be greatly helped by adopting a crop rotation regimen, where plants in the same family move to a fresh spot in the garden each year – the most common is a 3 or 4 year rotation.
Most likely the planting is suffering from Spinach blight, a virus spread by aphids, which causes yellow leaves and stunted plants. There is no cure for all virus infections as there are no chemical anti-viral sprays. You have to destroy the infected plants to protect your other plants from the virus. Discard them in the garbage, not in your compost or green bin. In the fall, make sure you do a thorough clean up of all the beds, cleaning up & disposing of all leaf matter & debris in your garden.
The addition of some well rotted sheep manure or good quality compost would improve soil structure, add nutrients, boost soil water retention and help control weeds. This does not need to be dug in, just spread on the soil surface as the worms & micro organisms will make sure it gets mixed in.
Next year, you should plant something different that is not affected by this disease. If you wanted to seed spinach, you should grow resistant varieties such as Blight Resistant Savoy, Savoy Hybrid 612 or Melody.