Signs of edema are noticeable on the tomato plant leaves, appearing as lesions. If the environmental conditions persist the tomato plant will continue to deteriorate, fruit production will diminish, and the plant will eventually succumb unless environmental conditions are changed (image courtesy: hortidaily.com).
By John Green, Certified Texas Expert Gardener, Orange County TX
It is my hope that each of you experienced a memorable Christmas and is ready to begin a new year! Spring will arrive before we realize it and there is always much garden preparation to accomplish before it does. Whether you enjoy planting ornamentals, vegetables, or both…now is the time to begin developing a planting strategy. It will soon be time to start germinating seeds for spring.
Most gardeners have over-wintered plants (me included) by relocating them inside our homes, porches, garages, or greenhouses. Protecting our plants by relocating them to interior spaces may be the right approach for preservation but the environmental conditions within these spaces can become problematic quickly leading to plant disorder known as edema. There are multiple causes of edema and some of the more common causes are overwatering plants, extreme humidity, poor air circulation, incorrect nutrient levels (especially potassium or calcium-low levels), and warm soil in conjunction with cool air temperatures- this is highly problematic when humidity is elevated, and the soil is saturated.
Edema is a disorder in plants (which is analogous to humans and other animals) that is caused by excessive build-up of water in plant tissues, faster than the transpiration process where leaves release water. The excess fluid ruptures cell membranes which cause the development of growths often located on the underside of leaves or indentations on the top side of leaves. These growths can have differing appearances depending on the plant species, such as hairy, needle-like structures, blisters, white ‘crusty’ protrusions, or become ‘squishy’.
Most broad leafed plant species are susceptible and in severe cases the growths can also appear on stems and cause leaves to turn yellow, or leaves can become distorted before falling off. If conditions causing edema are persistent the plant’s health will continue to diminish resulting in spindly, and stunted growth.
Edema can present ‘chameleon-like’ characteristics which are easily confused with other plant conditions where they “vacillate” or can be easily confused with other ailments such as mold, powdery mildew, nutrient imbalances, viruses, or pest infestations. Fortunately, edema isn’t a major concern, but it does require focused attention to avoid long-term plant issues, which if left untreated can cause distorted leaves and produce unsightly fruits. According to a study from Kansas City University (KCU), technically, edema is a buildup of water within cells which ultimately causes plant cells to stretch and then collapse.
Causes- Water is absorbed faster than the plant can use or expel it resulting in plant cell deterioration. The plant will show signs of collapsed cells. Environmental factors can include poor air circulation, an abnormal watering schedule, irregular fertilization, and crowded plants.
Signs- Symptoms of edema in plants include yellowish bumps or blisters on leaves, white crystallized bumps on the underside plant leaves, followed by brownish ‘dry spots’ where cells have collapsed. Many plants may have curled leaves because of edema. Some plants might show these symptoms on the plant’s stems or fruits. Severely affected plants will have distorted fruits and exhibit stunted growth.
Spread- plant edema is neither a viral nor a bacterial disease. It is a cellular disorder caused by environmental factors, meaning plant edema does not spread from plant to plant, though it can be more problematic for certain varieties such as broad leaf plants, i.e. peppers, tomatoes, ivy, ferns, cacti, broccoli, and numerous others.
Treatment- since edema is caused by environmental conditions, environmental changes are required to mitigate the disorder, followed by choosing to grow plant varieties which are less susceptible to edema.
Air Circulation– this will be of concern to greenhouse growers since plants need to ‘breathe’ by expelling oxygen and taking in carbon dioxide. Circulating air using a fan improves air flow, reducing stagnation and air quality is important, requiring ‘fresh’ air to be circulated consistently. Crowding plants together in a small growing space or greenhouse increases stress placed on them.
Space- plants need room to breathe no matter if inside a home or a greenhouse. Plants need ample space between them.
Watering- edema is caused primarily by an inability for plant cells to expel water quickly. Knowing this, it is important to know exactly how much water plants need and maintain a consistent watering schedule. Watering regimens vary from one plant type to another. Do not overwater!
Humidity- also plays a role in plant edema for some varieties. It is best to simulate plant growing conditions, such as if a plant is from an arid region growing conditions should be similar. Conversely, tropical plants require increased humidity (and fresh air) which can abate edema. Using a simple humidity/temperature gauge is appropriate for an indoor growing environment.
Imposters- edema can be treated by changing environmental factors but numerous other conditions appear like edema, listed below are a few “copycats”:
- Scale- are a type of insects which are small, white, and immobile which can easily spread from one plant to another. They are challenging to completely eradicate but are treatable using a neem oil solution or a pesticide. The area affected by scale is most often localized, while plant edema has a more crystalline appearance. There are many types of scale, so a bit of research will be necessary to determine the best approach to eradicate.
Powdery Mildew- is a common fungal disease that affects many plant varieties. Powdery mildew presents as a white, powdery substance like powdered sugar and occurs most often on the topsides of leaves, while edema will usually show symptoms on the leaf’s underside. This fungal disease spreads easily from one plant to another and requires early treatment. Treatments include a diluted solution of baking soda and dish detergent soap in water, sprayed on the affected areas.
Until next time fellow gardeners, let’s go out and grow ourselves a greener and more sustainable world, one plant at a time! Please send your gardening questions to: jongreene57@gmail.com
Social Media