Plant Disease

Plant Disease

Plant disease is a relatively complicated topic, simply because ordinary gardeners and farmers have difficulty distinguishing between symptoms caused by a specific plant disease (caused by fungi, bacteria or viruses), those caused by a common plant disorder (unfavorable nutrient, soil and/or weather conditions) or those caused by garden pests. Identification and diagnosis of plant disease in most instances is best left to a qualified nurseryman or State Extension Agent.

So, how do we save Mom’s favorite rose bush or the tomato plants which were looking so good a couple of weeks ago but now look ravished? Answer, if disease is the culprit, we don’t!

There are no practical solutions to curing plant disease. Unfortunately, the cure usually comes down to destroying the plant this year and starting over again next year. Therefore, prevention is the first line of defense against plant disease and is described under Organic Disease Control.

To help prevent the spread of plant disease, diseased plants should be immediately destroyed or removed by burning, burial in a remote location or disposal by the local trash collector.

The following is a very brief primer on the three types of plant disease that can infect your plants. Once you understand the basics, you can broaden your knowledge through literature readily available at your local library or by accessing the internet.

Fungi

Fungi are the primary cause of plant disease. Fungi can cause rotting of plant parts, wilt and sudden death, spots and blotches on plant parts, galls (swelling), mold or mildew, blistered or curled leaves, smuts (black sooty areas), rust (red-brown or yellowish) on leaves, and cankers (lesions on twigs or bark). Using a strong magnifying glass, you should be able to see either a fine threadlike web or tiny spore bearing stalks. Fungi spread by releasing spores which travel in water or moisture above and belowground and are also carried by the wind. The following measure will help control fungi:

• Good soil drainage
• Good air circulation
• Avoid gardening when foliage is wet
• Use watering methods that do not wet the leaves
• Rotate crops
• Immediately segregate plants that are diseased for disposal

Common fungal plant diseases include the following:
• Alternaria blight
• Anthracnose
• Scab
• Black spot
• Brown rot
• Club root
• Damping off
• Fusarium wilt
• Blight
• Root rot
• Verticillium wilt

Bacteria

Bacteria can cause a variety of plant disease. Many symptoms are similar to those caused by fungi. If bacterial rot sets in, it is often accompanied by foul odors, which are not present in fungal rot, one of the distinguishing characteristics. Also, plant disease caused by bacteria does not cause the threadlike webs or spore-bearing stalks characteristic of fungi.

Plant disease causing bacteria have a much shorter dormancy period than that caused by fungi. Bacteria can over winter in hibernating insects, old plant debris, cankers on living plants, and the soil.

Control of bacterial plant disease is similar to that described above for fungal disease. Common bacterial plant disease includes the following:
• Angular leaf spot
• Bacterial wilt
• Crown gall
• Fire blight
• Halo blight
• Potato scab
• Ring rot
• Soft rot

Viruses

The last plant disease topic is viruses. Over 300 viruses and virus-like organisms have been identified that attack plants. Common symptoms include stunting, abnormal growth patterns, such as leaf cupping or twisting, and leaves that are mottled or streaked with yellow or have ring-shaped spots. Disposal measures are as described above for fungi and bacteria infected plants.