Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
We have recently seen air pollution damage to greenhouse transplants. This can occur where coal or wood burning stoves are used and exhaust escapes when loading, where temporary unvented heaters are used in greenhouses, where heat exchangers in vented heaters have cracks, where exhaust pipes are leaking, or where fumes from burn piles or other sources are drawn into houses.
In fuel combustion, noxious gases can be produced if combustion is not complete. This can include: ethylene, sulfur dioxide, nitrous oxide and carbon monoxide. Even a clean burning furnace can have problems in airtight plastic greenhouses in cold periods where heaters are in constant operation. The level of oxygen can be depleted over several hours of continuous heating thus starving the combustion process of adequate oxygen and contributing harmful gasses.
During the combustion process, sulfur in fuel sources is converted to sulfur dioxide. If this leaks into the greenhouse and combines with the moisture there, sulfuric acid is formed. Low levels of sulfur dioxide may result in flecking and premature leaf drop. Higher levels can cause severe leaf burn, especially on young leaves.
Ethylene is a clear, odorless gas is a byproduct of the combustion of fuels. Ethylene can be damaging at levels as low as 0.05 ppm and even short exposures can cause leaf distortion, abortion of flower buds, defoliation and chlorosis. For more information on ethylene in greenhouses see the past article by Jerry Brust titled ‘Greenhouse Air Pollution Caused by Ethylene’ in WCU 17:6.