Plant Pathology Infobytes

January 5, 1998
Hints for Healthier Houseplants

Killing your houseplant with kindness? Or is it a fungus attack! In either event, the end result can be a dead plant. Unless the culprit is identified, and appropriate preventive steps taken, you're likely to run into the same problems when new plants are added to your collection. The following information and problem identification tips just might help solve some of your houseplant headaches.

Although some contagious diseases can be found on houseplants, if plants are purchased disease-free, fungi and bacteria generally cause little trouble indoors. Most homes and offices lack the high humidity necessary for the development of these diseases. Some diseases such as powdery mildew, can develop on plants growing in a bathroom or kitchen window since these rooms may have periods of high humidity.

Cultural problems arise when houseplant are subjected to adverse growing conditions. Light, fertility, water and temperature imbalances are most often involved.

Yellow, brown, or black spots can indicate a fungal or bacterial leaf spot disease. Leaf spots vary in shape and size depending on the organism and type of plant involved. A grayish-white powdery growth on stems and leaves is typical of powdery mildew.

Controls for foliar diseases include removal and destruction of affected leaves and maintaining adequate spacing between plants to promote air circulation. Also, avoid wetting the foliage and use a recommended fungicide or bactericide. However the disease should be accurately diagnosed before applying any pesticides.

The virus diseases that affect foliage plants often result in crinkled or curled leaves, or they may cause rings and streaks in the leaves. Viruses are normally moved from diseased to healthy plants by insects or on human hands. Plant infections are propagated when cuttings are taken from diseased stock plants. The best way to eliminate a virus problem is to discard the entire plant. Houseplant growers are urged not to purchase houseplant which are unthrifty looking since they may be buying a disease problem that could spread to healthy plants.

Root and stem rot diseases are caused by soilborne microorganisms. Lesions may form on the stem, especially near the soil surface, and girdle plants. In other cases, stems and crowns may become discolored, and soft and mushy. Diseased roots become brown to black and slough off easily.

The following are controls for houseplant root and stem diseases.

 

  • Use of sterile soil or sterile soil-less mix as a preventive measure. Moistened garden soils can be sterilized before use in an oven (180 degrees F for two hours) or microwave (15 minutes). Packages of sterile soil-less mixes may also be purchased.
  • Since root rot diseases occur under wet soil conditions, providing good drainage and avoiding overwatering can also help in controlling soilborne disease problems.
  • Avoid wetting stems and foliage when a stem rot is prevalent.
  • Some fungicide drenches are available for homeowner use, but these should only be used after the root rot pathogen has been correctly identified.
  • In many cases it may be best to just re-root a healthy portion of the plant in water or moist sand. The rooted cutting should then be replanted in sterile soil. Plants in the more advanced stages of disease should be completely discarded.

The following information may help to determine causes for common houseplant symptoms. Symptoms are listed and followed by possible causes.

  • Brown leaf tips, burned leaf margins - root injury from overwatering, drought, or excess fertilizer; excessive exposure to cold temperatures; low humidity; pesticide injury or mechanical injury; potassium deficiency; root rot diseases; or nutrient toxicity.
  • Pale foliage or yellowing of older leaves - air pollution, gas fumes; insect attack; insufficient fertility, especially nitrogen; or poor root health due to poor drainage, poor aeration, or pot-bound roots.
  • Pale foliage or yellowing of new growth - improper soil pH, or trace element imbalance.
  • Small, pale leaves, spindly growth - too much light, poor soil fertility; overwatering; or poorly drained soil.
  • Sudden defoliation - change in location and/or sudden change in light, temperature, or humidity; overwatering; or transplanting shock.
  • Brown, yellow, or black spots on leaves - fungal or bacterial leaf spot disease; overwatering; sunburn occurring when the plant is placed outside; or chemical spray injury.
  • Wilting or drooping of foliage, plants do not recover with watering - poor root health due to overwatering; drought; too much fertilizer; compacted soil; or root, stem, or crown rot disease.
  • Crown or stem is soft and mushy - crown or stem rot disease coupled with overwatering.
  • Roots brown, soft, or rotted - poor root health as a result of overwatering, drought, excess fertilizer, or root rot disease.

If you still can't identify the problem affecting your houseplant, give us a call at the County Extension Office, and we'll be happy to provide assistance.


Written by the late Dr. Frank Killebrew

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