Response of Plants to Vapor Heat Treatment
Stacey Chun, Arnold Hara, Christopher Jacobsen, Tsuyoshi Tsumura (College of Tropical Agriculture
and Human Resources, University of Hawaii at Manoa), Van Kashiwamura (Plant Quarantine, Hawaii
Department of Agriculture), and Koji Okamura (Diamond Head Papaya)
Vapor heat is an approved USDA fruit fly quarantine treatment for papayas that are exported
to the U.S. mainland and Japan. Vapor heat is heated air maintained at greater than 90% relative
humidity. Preliminary trials by Hawaii Dept. of Agriculture and UH-CTAHR indicated that vapor
heat at 113o F for 15 min is effective against eggs, juveniles and adult coqui frogs. Would it be
possible to disinfest potted-plants of coqui frogs without any heat damage to plants?
A commercial vapor heat chamber (Diamond Head Papaya Co., Keaau, Hawaii) with a
capacity of 20 pallets (maximum height 6 ft.) was used to treat over 42 species and varieties of plants
in September 2002. Potted-plants were obtained from nurseries and equally divided in half. One-half
of the potted plant species or variety was untreated and the other half was palletized and treated. The
chamber temperature was raised from ambient temperature to 113oF (>90% RH) and held for 15
minutes. The total treatment length was approximately 45 minutes. After the heating process, plants
were drenched with ambient temperature water to reduce phytotoxicity. Plants were observed and
maintained for 4 weeks after treatment. Only dendrobium and epidendrum orchids were confirmed to
suffer significant heat damage with lesions and fading in flower petals (see photos). Citrus suffered
damage to very young leaves, but nurserymen concluded that this is tolerable with no sustained
effects. More tests are needed with certain species to confirm heat damage. (bromeliads, vanda,
oncidium, Dracaena ‘Lisa’).
Heat injury appears to intensify mechanical and insect injury, and nutritional deficiency and
disease symptoms. Pesticide (insecticide or fungicide) residue may also intensify heat injury.
Apparently, healthy, non-stressed plants are more tolerant to heat treatments. Preliminary analysis
indicates that vapor heat may be economically feasible as an interisland quarantine treatment for the
coqui frog.
Degrees of tolerance of tested plants to vapor heat treatment
Tolerant
Palms:
Phoenix
Areca
Triangle
Fishtail
Sago
Rhapis
Parlor
Kentia
Aglaonema
Anthurium:
‘Kalapana’
‘Marian Seefurth’
‘Maunakea’
‘Lady Jane’
Calathea
Citrus (only tender,
emerging growth burned)
Chrysanthemum
Dieffenbachia
Dracaena warneckei
Dracaena fragrans
Dwarf apple banana
False heather
Gardenia
Guava
Maiden hair fern
Miracle berry
Mock orange
Mulberry
Passion fruit
Philodendron
Streptocarpus
Syngonium
Ti plant
Heat Sensitive
Dendrobium orchid
(Flowers faded; lesions on leaves)
Epidendrum orchid
(Lesions on some leaves)
More Research Needed (Inconsistent results)
Chamaedorea
Dracaena ‘Lisa’
Oncidium orchid
Bromeliads: ‘Puna Gold’, ‘Rosy Fireball’, ‘Orange Crush’
Vanda orchid
Plants donated by: Bromeliads Hawaii, California-Hawaii Foliage, Flowers Inc., Gines Orchids, H. Eunice
Nursery, Hale Pua Nursery-Hawaii, Hawaiian Sunshine Nursery, Kurtistown Nursery, Plant It Hawaii, Puna
Certified Nursery, Royal Palm Enterprise, and Schaffer Family Farm.