Prevention of Plant Diseases

By Mary Bernard, Master Gardener

Prevention is the best remedy when it comes to dealing with most plant diseases. Many diseases cannot be effectively controlled once symptoms develop or become severe. Fall is a good time to launch your preventative management program in the home orchard and garden. This includes a combination of strategies involving sanitation, cultural practices, and seasonal spray applications.

Garden sanitation aims to remove the source of future disease infections by means of a thorough clean up program. Common fungus diseases like peach leaf curl, brown rot, apple scab, camellia petal blight, and black spot on roses will reappear the next season because the fungus spores survive over winter in dead leaves, rotting or mummified fruit and other plant debris left behind the previous Fall. Disease pathogens can also survive in older mulching material laid out in previous years. If a serious fungus infection exists, such as Camellia Petal Blight, remove old mulch and replace with fresh material. Grab a rake and get out into the garden for a clean up day before first rainfall for best results. Dispose of any suspect plant debris.

Removal of diseased plant tissues on the plant itself is your next line of defense. Prune out diseased foliage, twigs or branches, hand pick blighted camellia blossoms as they appear and dispose of these in the trash. Avoid unnecessary pruning; pruning causes wounds, which can be entry sites for decay and disease organisms. Sanitize pruning equipment to avoid transmitting disease to healthy plants.

Avoid overhead irrigation splashing water spreads fungal spores and wet foliage promotes some foliar and fruit diseases such as leaf spots, rusts, anthracnose, and brown rot.

Finally, follow up with preventative applications of a fungicidal spray. This is an especially critical step in the control of peach leaf curl and other recurring diseases. Synthetic and organically acceptable spray materials are available to control certain plant pathogens, primarily fungi. Products such as Bordeaux mixture, sulfur, fixed copper, and fungicidal soap sprays protect plants from pathogen infection. These organically acceptable fungicides generally only prevent the infection of healthy, spray-covered tissue and do not act systemically to kill existing pathogens; therefore repeated applications may be necessary during critical growing stages. Synthetic fungicides are often more effective, easier to apply, and are less likely to damage susceptible plants; some have systemic activity. Fungicides require careful timing to be effective. Consult a qualified nursery sales person to determine an appropriate spray product for you. Wear protective gear such as goggles and gloves, and use as directed on the product label.

Other Master Gardener articles about specific disease pathogens:

         Oak Galls

         Oak Root fungus


         Root Rot

         Rose Diseases

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request .Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM. You may also call the Paso Robles office at 237-3100 on Wednesdays from 9 AM to 12 PM. The San Luis Obispo Master Gardeners website is at Questions can be e-mailed to: