Also known as senescence hormone, ethylene (C2H4) is an odorless and natural plant hormone produced as gas. It damages plants and flowers by making them age early. This harmful pollutant of ornamental plants is also called the death hormone because of its ability to speed up plant growth. It exists naturally in plants that are rotting, aging or decaying, and unnaturally from materials improperly burned or combusted.
Symptoms of ethylene damage depend on the sensitivity of the flower to the gas, the duration of exposure, the temperature at the time of exposure and the concentration of ethylene. General symptoms include leaf yellowing, shattering or shedding of petals, leaf or flower abortion, flower or bud dropping, stunted growth, malformed leaves or flowers and rapid flower wilting.
Sources of ethylene include cigarette smoke, exposure to damaged, decaying or dying plants or dirty buckets, kerosene fires and wood coal, contaminated fuel, exhaust from engines of cars and forklifts and contact with ripe or decaying fruit. According to the Commercial Floriculture Resource Newsletter from Ohio, the leading cause of ethylene damage in a greenhouse is an improperly functioning heating unit.
Some flowers are more sensitive or susceptible to ethylene damage than others. According to the Agriculture and Landscape Program Fact Sheet, impatiens, orchids, geraniums, snapdragons, carnations and saliva are extremely sensitive; coleus, roses, begonia, chrysanthemums and petunias are moderately sensitive; and marigold, zinnia, alyssum and ornamental peppers are insensitive to the gas. Exposure of 100 ppb (parts per billion) over a span of a few hours causes irreversible damage in sensitive flowers. In less sensitive flowers, however, this amount of exposure causes damage in a few days or weeks. Mature buds and flowers are more susceptible to ethylene damage, and the extent of damage increases in warm temperatures.
Store plants at temperatures around 34 degrees F to minimize ethylene damage, and ensure good air circulation and proper ventilation to diffuse concentrated amounts. In a greenhouse, avoid using truck and tractor engines in closed areas near growing flowers, and clean plant debris and pruning and professionally service burners and boilers at least once a year. Do not store flowers with rotting fruit, and avoid bruising or mishandling plants. Display flowers in shaded, cool areas, away from direct sunlight. More ethylene is required to induce plant disorders in low temperatures.
Silver thiosulphate (S.T.S.) is an effective treatment measure for ethylene damage. Most flowers susceptible to ethylene damage respond well to measured and timely applications. Florissant 100 is a commercial treatment used by florists.