by Courtney Llewellyn
Ethylene (C2H4) is nothing more than a plant hormone that controls flowering and rooting. It’s known as the “ripening hormone,” which is why some things can be picked or cut green. It can be a boon or a burden. When it’s a problem, there are ways to mitigate its deleterious effects.
Dr. Michelle Jones, a professor in the Department of Horticulture and Crop Science at Ohio State, presented “Recognizing and Preventing Ethylene Damage in the Greenhouse” at the most recent Great Lakes Expo. She said ethylene affects plants at all stages of greenhouse production and the marketing chain – and can decrease plant quality and shelf life.
Sources of Ethylene
Ethylene can come from improperly functioning or improperly ventilated heating units, exhaust from combustion engines (gasoline or propane), leaky gas lines or contaminated fuel, cigarette smoke, dying and decaying plant material and wounded plants. The number one source is unit heaters. “Keep an eye on maintaining heaters in all stages of their lives,” Jones said. “You want that exhaust out of the greenhouse.”
She recommended following the 3-2-10 rule for chimneys and exhaust: Your chimney’s shortest side needs to be at least three feet above the roof penetration, and its top has to be two feet higher than any part of the building that’s within 10 feet.
Flowers naturally produce ethylene as they die. Carnations, for example, peak at day six post-harvest, and tomatoes and apples do the same thing. “You’ve heard ‘One rotten apple ruins the bunch.’ That apple is ethylene,” Jones said.
Fortunately, as a gas, it’s fairly easy to remediate. Whatever space it’s building up in just needs to be ventilated.
Symptoms of Ethylene Damage
Jones noted many ways in which ethylene damage makes itself known. It can be the shedding or shattering of petals; bud, flower or leaf drop; rapid flower aging and wilting; drooping of leaves or bracts; flower bud abortion; leaf yellowing (chlorosis); malformed leaves; and stunted growth. It can look a lot like nutrient damage, however, and it may be difficult to diagnose.
Additionally, some plants are more sensitive to ethylene than others. Anthuriums, gerberas, tulips, mums, African violets, cyclamens, marigolds and zinnias are all much hardier when dealing with the gas than carnations, petunias, orchids, snapdragons, geraniums, fuchsias, streptocarpuses, primulas and tomatoes. Jones added that portulaca will lose its flowers and leaves if it’s heavily affected. There are also cultivar differences in sensitivity.
The severity of injury is influenced by many factors – the sensitivity of the plant, the concentration of ethylene, the length of exposure and even the temperature. Jones noted, “Sensitivity is higher at high temperatures, lower at low temperatures.”
Young buds tend to be less sensitive than open flowers. Flowers are more sensitive than leaves. And younger plants are more sensitive than more mature plants.
Recovery from Ethylene Damage
“Can plants recover? It depends on what you want to do with them,” Jones said. “Will they be saleable? Probably not. Will they still be alive? Likely.”
How do you know if you have an ethylene problem? Jones suggested using an indicator plant, like tomatoes, since they’re so sensitive. A proactive approach is good, with a major focus on ventilation. You could also use gas chromatography to measure the percentage of the gas in the air.
“You can prevent damage during production with the proper maintenance of heating units and ventilation,” Jones reiterated. She said, if possible, use electric carts and forklifts. And make sure to clean up dying and damaged plant material.
Jones said you can prevent damage during storage using scrubbers containing potassium permanganate, which remove ethylene. Prevent ethylene damage during shipping using anti-ethylene compounds, such as 1-MCP, or use EthylBloc sachets.
“Knowing the potential sources of ethylene and which plants are sensitive will help you recognize potential ethylene problems,” Jones said.