Ozone treatment has many advantages for control of fungal diseases. There are no residue concerns, no registration is required, and it is non-specific, therefore potentially effective against a broad spectrum of pathogens. However, ozone is known to cause plant damage. There is little information available on either the ozone tolerance of floriculture crops or the levels required to kill plant pathogens under commercial conditions. Nine floriculture crops (begonia, petunia, Impatiens, Kalanchoe, pot roses, pot chrysanthemums, lilies, snapdragons and Alstroemeria) were subjected to increasing levels of ozone. Trials were conducted at 5 and 20 °C (90% to 95% RH) and ozone exposure was for 4 days for either 10 hours per day (simulating night treatment) or for 10 minutes every hour. Damage was assessed immediately after treatment and after an additional 3 days at room temperature in ozone-free air. Trials were terminated for the crop when an unacceptable level of damage was observed. Trials to determine the lethal dose for actively growing pathogens (Alternaria alternata, Alternaria zinniae and Botrytis cinerea) and fungal spores were conducted under identical conditions. Ozone tolerance varied with plant type and ranged between <0.2 and 3ppm. Generally, the crops surveyed were more susceptible to ozone damage at the low temperature. As a group, the bedding plants were the least tolerant. Fungal spores were killed at treatment levels between 0.8 and 2 ppm ozone. The actively growing fungal mycelium was still viable at 3 ppm ozone when the trial had to be terminated due to ozone-induced structural damage in the treatment chambers. Under the trial conditions, only the Kalanchoe would be able to tolerate the high levels of ozone required to kill the fungal spores.
Lisa J. Skog*, Theo Blom, Wayne Brown, Dennis Murr and George Chu
Wayne Brown, Theo J. Blom, George C.L. Chu, Wei Tang Liu and Lisa Skog
The sensitivity of easter lilies (Lilium longiflorum) to either ethylene or methane (products of incomplete burning in gas-fired unit heaters) was tested during rooting [3 weeks at 18 °C (65 °F)], vernalization [6 weeks at 6 °C (43 °F)] and subsequent greenhouse forcing (15 weeks at 18 °C). Starting at planting, easter lilies were exposed for one of seven consecutive 3-week periods (short-term), or for 0, 3, 6, 9, 12, 15, 18, or 21 weeks starting at planting (long-term) to either ethylene or methane at an average concentration of 2.4 and 2.5 μL·L-1(ppm), respectively. Short- or long-term exposure to ethylene during rooting and vernalization had no effect on the number of buds, leaves, or plant height but increased the number of days to flower. Short-term exposure within 6 weeks after vernalization reduced the number of buds by 1 bud/plant compared to the control (no ethylene exposure). However, extensive bud abortion occurred when plants were exposed to ethylene during the flower development phase. Long-term exposure to ethylene from planting until after the flower initiation period resulted in only two to three buds being initiated, while continued long-term exposure until flowering caused all flower buds to abort. Short-term exposure to methane at any time had no effect on leaf yellowing, bud number, bud abortion, or height and had only a marginal effect on production time. Long-term exposure to methane from planting until the end of vernalization increased both the number of buds, leaves and height without affecting forcing time, leaf yellowing or bud abortion.