Above: Hosta with symptoms of leaf spots and necrosis.
Do your landscape plants have cankers, mosaics, galls, mummies, or witches’ brooms? These and other symptoms are often hard for the average homeowner to understand, let alone visualize. Purdue Extension staff can often help homeowners with plant disease diagnosis.
Additionally, Purdue Extension specialists Janna Beckerman and Tom Creswell authored a publication entitled, “Symptoms and Signs for Plant Problem Diagnosis – An Illustrated Glossary.” It is designed to help homeowners understand plant disease symptoms and signs, one of the first steps in correctly diagnosing a disease or abnormality and subsequently formulating a strategy for management, if needed.
There is a difference between symptoms and signs. The authors explained that a symptom is a change in plant growth or appearance that may indicate or describe a plant health problem. For any given symptom, however, there could be multiple causes of that observed change. They explained that a sign, on the other hand, is the evidence of the damaging factor – the actual cause of the problem that allows you to conclusively diagnose a plant health problem. Examples of common signs would be catching a fat green tobacco hornworm chewing on your tomato plants or the fluffy white mycelia of white mold in beans. A comparative parallel on a crime scene may be the presence of the fingerprints of the perpetrator, for example.
I’ll cover a few of the more common symptoms I’ve encountered with local homeowners and ones that you may notice in plants, as explained by the authors. Consult the publication for illustrations and descriptions of a wider array of symptoms and signs.
Chlorosis is the yellowing or loss of color in normally green tissues due to the destruction of chlorophyll. Chlorophyll is an essential component of photosynthesis in plants, and it makes leaves green. Insects, pathogens (causes of plant diseases, such as fungi or bacteria), and abiotic disorders (non-living, non-infectious factors, such as environmental factors or nutrient deficiencies) can cause chlorosis.
Cankers are localized, cracked, or sunken lesions on a branch, stem, or trunk. Growth can girdle infected plant parts, resulting in blight or dieback. Cankers are typically caused by bacterial or fungal pathogens.
Galls are a tumor, swelling, or outgrowth of disorganized plant tissue. They are commonly found on leaves, twigs, or crowns of plants. They can be caused by pathogens, insects, or as a response to injury.
Leaf spots are localized destruction of the chlorophyll by the feeding of pathogens or sucking insects. There are many types of leaf spots, caused by fungi, bacteria, nematodes, viruses, insects or mites, algae, and abiotic disorders.
Mosaics are dark green, light green, and/or yellow areas forming a variegated pattern. It is caused by a virus.
Mummies are dried, shriveled fruit, partly composed of fungal material. Fungi cause mummies.
Necrosis is the term for the death of plant tissue, resulting in the tissue turning black or brown.
Needle cast is a name given to foliar diseases in conifers where plants shed or cast off the needles. They are caused by fungal pathogens, although some insects can also consume needles to similar effects.
A witches’ broom is an abnormal, brush-like growth of many weak shoots. It often looks somewhat similar to broom bristles on a plant. Insects, fungi, bacteria, or viruses can cause witches’ brooms.
Find the resource, number BP-164-W, at the Purdue Education Store, www.edustore.purdue.edu.