Abiotic Diseases – Frost Injury
When we talk about diseases, we often think about teeny, tiny “no-seeum” critters – living organisms like fungi, bacteria, viruses and nematodes causing disease. These are all causes of biotic (living) disease. According to Merriam-Webster’s dictionary, the definition of disease is a condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms. At this time of year and going forward into early spring we sometimes can see evidence that certain plants have experienced harm and their functioning is adversely affected. It’s normal to ask “what’s eating (killing) my plant? However, consider the term Abiotic Disease.
Abiotic diseases are caused by non-living things: weather, drought, nutrient deficiencies, etc. We may see different leaf textures, colors, curls, or other problems like wilting or dieback in the foliage. If there are no signs of arthropod (such as insect, spider, or crustacean) pests (molted skins, webbing, poop, or the actual pest) coming to munch or set up house, abiotic disease may be the culprit. Also, it often turns out that the original problem is found in the lower stem or the roots. After all, half of that plant is underground!
There are a number of abiotic clues to look for to determine if it’s a living organism or non-living agent that’s the cause of the plant failure. Frost damage can be one that we don’t expect as we tend to see the result when it warms up, not necessarily at the time of freezing events.
The age of the plant tissue affected can provide clues to cause. Living organisms would attack all ages of tissue. If there is widespread, contiguous damage to the plants’ new leaves, especially the lower ones that come out in the spring, they might’ve had some cold injury or frost injury. Knowing what the plant looks like in normal conditions is the place to start. Paying attention to what you observe in your plants within the parameters of time and space and keeping an eye out for similarities can tell you a lot.
Leaves and stems damaged or killed by spring frost are usually small and succulent at the time of injury. Damaged leaves often have jagged open spaces which are similar to feeding holes by chewing insects. Leaves that have been killed first appear water-soaked and soon become shriveled and reddish brown to dark brown or nearly black, depending on the species. Dead leaves or shoots break off or fall off during the following several weeks. New shoots and leaves begin to grow from dormant or adventitious buds almost immediately and soon mask the early season damage.
Woody plants undergo seasonal changes in their ability to tolerate low temperature. In autumn, perennial plants become acclimated to withstand low temperature. The degree of cold acclimation varies during winter in relation to ambient temperature. As temperatures rise in late winter and early spring, plants de-acclimate until, by the time growth begins, they can no longer tolerate more than a few degrees.
The most common external symptoms caused by winter freezing are dieback, foliar browning, sunscald, and bark splitting on branches or the trunk. Dieback of twigs and branches, and foliar browning in evergreens, commonly follow freeze injury when winter temperatures arrive suddenly after warm autumn weather below freezing. Most damage by freezing during winter follows untimely de-acclimation during temporary warm weather. Often after a period of unusual warmth, the temperature drops rapidly to a level normal or subnormal for the season.
Non-living causes of plant tissue failure are natural, but sometimes it happens because of the intended and unintended acts of humans. Herbicide damage, weed-eater damage, improper original planting technique, etc. all can pile up to be challenges the plant just cannot overcome. Timely observation and “know before you grow” habits are valuable skills for the gardener as abiotic injuries can be attractive entry points for insects and pathogens looking for an easy meal.
To learn more about this and issues related to plant diseases and disorder, go to the 5 Diseases and Disorders publication.
Minda Daughtry is the Horticulture Agent for North Carolina Cooperative Extension in Lee County.