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Organic Disease Control


The old maxim "an ounce of prevention is worth a pound of cure" takes on real meaning in organic gardening, as the key to successful organic disease control lies in raising healthy plants and avoiding diseases. Healthy plants are less likely to contract a fungus, bacterium, virus, or to succumb to stress. If they do develop a problem, healthy plants are better able to withstand and overcome the problem.

Following are some organic gardening suggestions which will help reduce the incidence of plant disease:

A. Whenever possible, choose disease-resistant plant varieties. Nursery and seed catalogs are good sources of information on disease-resistant plant varieties. Your state’s University Extension Services also usually publishes lists of suggested resistant varieties.

B. Buy disease-free seed each year from a dependable seed dealer. Some organic gardeners save seed from their favorite varieties. When saving seed, make sure the plants from which the seeds were harvested have no disease symptoms.

C. Clean up and dispose of all old and diseased plant debris before planting anew. Do not compost diseased plant residue. Also eliminate weeds around the perimeter of the garden, because weeds can serve as hosts for plant diseases.

D. Select and plant only disease-free plants from the nursery. Carefully inspect transplants for any spots or lesions, or other signs of disease, on the stems or leaves. Remove a few transplants from the container and inspect their root systems. Healthy roots are light in color, and show no signs of decay or excessive wrapping. Avoid plants that have already set fruit.

E. Create a good growing environment....lots of sunlight, good air circulation, low humidity, well-drained soil, away from large trees and low areas, with adequate growing space between plants. Plant diseases thrive in the opposite conditions.

F. Rotate crops in the garden each year. Crop rotation helps prevent a build-up of diseases in any one area.

G. Trim bushy plants. Many plant diseases hide and thrive in the dark recesses of bushy plants.

H. Control insects, especially aphids, leaf hoppers and cucumber beetles, which can transmit some viral and bacterial diseases.

I. A 4"-6" organic mulch, such as hay, compost, straw, newspaper or wood shavings, can aid in disease prevention by reducing direct contact between soil and the plants.

J. Root out and destroy any plant showing severe disease symptoms, in order to prevent the spread of disease to adjacent plants.

K. Organic and biological fungicides are available to organic gardeners. The Organic Materials Review Institute (OMRI) www.omri.org reviews and approves materials to be used in organic gardening. Organic growers should check the OMRI list before applying any new chemical.

L. Clean garden tools after use. Plant diseases can be picked up on pruning shears, scissors and other gardening tools, and then get transmitted by using the infected tool again on a healthy plant.

In summary: planting resistant varieties, keeping the garden clean and free of diseased leaves and plants, and following gardening practices which suppress the development and spread of disease organisms, goes a long way in controlling disease problems in the garden.

Missouri Botanical Garden, 2001-2011