Identifying Plant Disease

A little background about how diseases occur in plants. We start from the mode of transmission and then we can identify what type of disease organism that has invaded the plant.

Things to ask yourself and then report to your local nurseryman or extension specialist are; what types of insects are present on the plant, the soil makeup, sun exposure, and how much or little moisture is present in the plant. Is the plant in cool or hot temperatures, what fertilizers were used, and if you have recently done any pruning or have applied chemicals to or around the plant. If you can determine where the damage is, it is also helpful for identification and what type of control to use.

Diseases caused by bacteria have characteristics that can include being parasitic, and show rapid multiplication. Bacterial organisms lack chlorophyll and are smaller organisms than those of fungi. The most common route of invasion by bacteria is through wounds caused by physical contact by insects, mites, rain or wind and by transplanting or pruning.

Fungi feed on live tissue and are more aggressive than bacteria. 90% of all fungi are parasitic. Further fungi show up as slow and unusual growth, loss of fruit and flowers, chlorosis, exuding sap, a water relationship that is abnormal, the presence of fruiting bodies called spores or discoloration of foliage, galls or cankers, mosaic or blotches on leaves, blights or scorching of limbs, rotting or wilting of roots.

Viruses are illustrated in plants by the reduction in overall growth or reduced yields, color changes, flower loss, abnormal growth patterns such as crinkled leaves or leaves with a “measles” like texture, and sudden death. Symptoms of viruses depend on the time of the infection, temperature, and the virus strain itself and the presence of other viruses or diseases.

Viruses can be detected but cannot be stopped once infection has occurred. Unlike fungi and bacteria, the organisms of viruses are smaller and can change and adapt to many situations. Viruses are also spread by insects, soil transmission by nematodes, fungi, bacteria or unsanitary potting situations, by seed transmission, or by physical damage, viruses can be spread to healthy tissue by diseased tissue whether dead or alive.

The easiest ways to avoid diseases in plants are; to clean tools and pots with a 10% bleach solution after each use, discard pots and trays where a disease has already been, use sterile potting soil when planting seeds and use seeds from reputable dealers. Do not bring home diseased plants and keep pests and weeds from your plants. Keep watering equipment off the ground where the diseases can be transferred to the plants as you water.  Prune during the correct season for the plant, sanitize with each cut, and to leave room around plants when you mow or weed whack.

Fungicides can control fungal problems, bacterial problems can be pruned out and burned or can be controlled by bactericides. Viral infections on plants must be culled and burned immediately as they will remain viable and have the ability to adapt and change to their environment so chemical or cultural methods do not work.

A good reference to know about for disease control in Washington is the Pacific Northwest Plant Disease Control Handbook that is revised annually through the Extension Services of Oregon State University and the Washington State University and the University of Idaho.

Happy Gardening!

Kellie Smith, September Song Nursery 274-8853 Toutle, WA on the web at www.septembersong.net