Why do vegetables continue to die no
matter how many times I replant? There are
soil borne plant diseases that can survive in the garden, either on plant
debris or in the ground itself. Once infected, the soil can
remain so year after year. Some of these
diseases have a wide host range, while others attack either one particular species
only or may attack members within a particular plant family. Planting the same crop year after year in the
same location will allow for the pathogen to build up to high levels.
One of the
best control measures for the soil borne diseases is crop rotation. This will
allow time for the plant debris to decay and the associated pathogens to die
out. The time required for this to happen varies. Some diseases survive up to 10 years or more,
but most recommendations suggest periods of one to four years before
returning to the original crop.
Keep in mind
that a fungus that attacks, for example, the roots of lettuce will usually not
attack beans. If tomatoes are being grown one year, do not come back and plant
tomatoes again, or potatoes, peppers and eggplant for that matter – they are
all in the same family. This is a good
practice even if no diseases are detected.
Another
important step in disease prevention is to take advantage of any resistant
varieties that may be available. For vegetables, check with seed catalogs to
see if they have varieties that are resistant to a specific disease. The same is true
with fruit trees since certain varieties are more resistant to diseases.
Note: resistant (or tolerant) does not mean
immune. A resistant plant will be less affected by the disease and show fewer
symptoms. A plant that is immune will
not be affected by the disease. Unfortunately, some resistant varieties may
lack certain desirable characteristics in the plant such as flavor or high
production. If you can find resistant varieties, the battle against disease is
half over.
Ask the Garden Guy, Science Based Answers to Garden Questions, is an excellent resource book for gardeners. Some popular topics
include Slugs and Snails, Organic Pesticides, Why Vegetable Seeds Do
Not Germinate, What’s So Hot about Manure? Mushrooms in the Lawn. Purchase by clicking on the image of the book above.
