Hydroponics Garden Diseases


Plant diseases or blights in a hydroponics garden are much less frequent than in a dirt garden because there is no dirt to grow bacteria. Not to mention the fact that many plant diseases travel to the plant from the surrounding soil.

Infectious Disease in Plants

The cause of all plant disease can be narrowed down to 1 of 5 categories:

  • Fungi - members of the plant kingdom, they attack and feast upon other plants to obtain food,
  • Bacteria - microscopic single-cell organisms that enter the plant through 'wounds',
  • Viruses - cell walls of plants provide a natural barrier against viruses,
  • Water Molds - small organisms that resemble fungi but are distinctly different,
  • Nematodes - soil based roundworms.

Plant disease cannot occur without a host plant, a pathogen and favorable environmental conditions.

Plants can be more susceptible to disease if weakened by environmental conditions such as too much shade, high humidity and crowded conditions. They are also more susceptible when weakened by nutrient deficiency or toxicity (too many nutrients) and poor pH.

There will always be some trouble with disease, just watch for it and take care of it immediately. Unfortunately many disease cures involve the use of harsh chemicals which you really do not want on your plants.

A hydroponics garden can easily collect such chemicals in the nutrient solution with indiscriminant use and get into the plant cells - not something you want...

I usually try some less harsh solution first. My favorite all-purpose cure is to mix together water, baking soda, lemon juice and a very little dish detergent. I put this in a spray bottle and mist the affected parts of the plant. Sometimes it works like a charm and sometimes not.

Bordeaux Mixture

A mixture to the ratio of 4-4-50 is prepared of 4 parts (6.5 cups) copper sulfate or bluestone, 4 parts (6.5 cups) lime and 50 gallons of water.

The home hobbyist can make a smaller batch for a hydroponics garden using 2 tablespoons copper sulfate, 2 tablespoons lime and 1 gallon of water. This mixture does not store well so be sure to use it the same day.

If you mix and use this recipe, make sure you cover all areas open to your nutrient solution or the dish detergent will get into it causing soap bubbles.

I usually have to use a harsh chemical twice a season in my hydroponics garden in which case I cover the base of the plant and any open nutrient solution and spray sparingly.

An all-purpose approach to plant disease, unfortunately not very organic, is the Bordeaux mixture consisting of finely ground lime and copper sulfate.

This mixture has been used as a foliar spray for fungal infections for over a century; mainly in vineyards in France and is very effective. Its main drawback is the leaching of the copper into groundwater.

A new approach to plant disease control is really a 'rediscovered' approach known as biofungicide. This is a method of attacking plant infection through the use of naturally occurring and unmodified bacteria and fungi.

Sometimes it can be hard to distinguish between a nutrient deficiency, pest or disease but with experience you will be able to make an educated guess.

The following table will list some of the most common plant diseases.

DiseaseSymptoms Treatment
Rust Slightly raised, powdery red pustules on the underside of the leaves causing them to turn yellow then brown and die. Helped along by high humidity. Very contagious.Apply harsh chemicals like zineb or maneb.
Club Root Roots turn into a mass of club shaped tubers. Plants may become stunted.Dust with fungicide.
Damping Off A fungus affecting small plants where stems meet soil causing them to fall over and die. No treatment.
Crown and Stem Rot Fungus causes plant to turn pulpy and rot.Cut away rotted plant portions and spray with a fungicide.
Root Rot Fungus rots a plants roots. Cut away rotted root portions and spray with a fungicide.
Powdery Mildew Fungus causing whitish spots on the underside of the leaves. Eventually the leaves shrivel and die. Thrives in high humidity.Spray with homemade all-purpose cure described earlier.
Early Blight Dark brown spots on leaves , stems and plant fruit seriously weakening the plant.Treat with harsh chemicals (maneb, zineb).
Black Mold Sooty black or grayish white leaf growth.Gently wash leaves and scrape off mold.
Anthracnose Fungus caused by over-watering where leaves become marked with dark smears and shrivel. Hardly ever occurs in hydroponics plants Spray with fungicide and remove damaged leaves.
Botrytis Grayish white, fuzzy leaf growth caused by inadequate ventilation. Not common in hydroponics gardens.Increase ventilation and remove affected leaves.

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