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| Tomato pollution damage (Photo: E. Lookabaugh) |
Winter may have finally arrived, and with it, a serious issue for greenhouse growers. Over the past few weeks, the Plant Disease and Insect Clinic has received several tomato samples showing symptoms of pollution damage. The most common greenhouse pollutant is ethylene. Ethylene is an odorless, colorless gas which acts as a plant hormone. Ethylene is a growth regulator in plants, and excess ethylene is harmful to greenhouse crops. Tomatoes are particularly sensitive to ethylene and other pollutants like propane. Repeated exposure to very small amounts (0.01 ppm) over several days or exposure to higher amounts (1 ppm) for several hours can result in injury.
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| Tomato pollution damage, twisted leaves (Photo: E. Lookabaugh) |
The most common symptoms of ethylene exposure on tomatoes are epinasty (a downward bending of growth that causes plants to appear droopy even though they are not wilted), flower drop, and twisting of the upper leaves.
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| Tomato pollution damage, pale leaf spots (Photo: E. Lookabaugh) |
Tomato plants exposed to high levels of propane gas can have superficial stem lesions on one side of the plant (the side that faces the heating system) and leaves with tan to white lesions between the veins. Tomatoes will usually recover once they are no longer exposed to pollutants.
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| Tomato pollution damage, stem lesions, flower death/ drop (Photo: E. Lookabaugh) |
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| Tomato pollution damage, superficial stem lesions (Photo: E. Lookabaugh) |
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Tomato pollution damage, stem lesions
and flower drop (Photo: E. Lookabaugh) |
Faulty heating systems are usually the cause of pollution damage. The major causes of gaseous pollutants in a greenhouse system include dirty or improperly adjusted heating units, cracked heat exchangers, leaky gas lines, chronic use of unvented heaters, and exhaust from combustion engines. Pollutants can build up in the greenhouse when temperatures are borderline, causing heaters to kick on and off many times during the night. Exhaust from heaters that are not vented properly will lead to a build-up of incompletely combusted gases. Additionally, the any exhaust remaining in the exhaust pipe will flow back into the greenhouse. Alternatively, if nights are very cold and the heater runs a lot, insufficient oxygen feed can result in incomplete combustion and pollution damage.
Here are a couple of solutions to pollution issues in your greenhouse system.
- Under cold conditions when ventilation systems are shut down, make sure the heater has access to a sufficient supply of oxygen. The grower may need to add an air intake source that feeds the heater.
- Make sure pollutants are properly exhausted. If there is a crack in the heater or exhaust pipes, pollutants will remain in the greenhouse. There should be a small fan in the exhaust pipe that blows for about 20 seconds after the heater (and the heater fan) shuts off to be sure all pollutants exit the exhaust pipe. In a "vent-free" system, the first and last puffs of air should be exhausted because "vent free" heaters are 99% efficient except when they start and stop.
For more information on ethylene damage: click here
For more information on faulty heaters: click here
