NAPHTHALENE AS A GREENHOUSE FUMIGANT 21 



forceful syringing or by improper growing conditions, and it frequently appears 

 that the naphthalene only hastens and aggravates the injury, which is primarily 

 due to the poor health of the plant. 



Occasionally colored blooms and buds, especially carnations and roses, have 

 been bleached by a prolonged exposure to naphthalene, injury of this kind 

 being more frequent when the growth is abnormally soft and tender. 



TOLERANCE OF PLANTS TO NAPHTHALENE FUMIGATION 



The tolerance of plants to naphthalene fumes differs greatly. Hartzell (6 

 and 7) has classified a large number of species and varieties according to their 

 susceptibility in his experiments, and most of the species which are grown in 

 New England greenhouses have been fumigated experimentally by the writer. 

 As a result, certain species of plants are known to tolerate the treatment and 

 others very definitely will not, thus dividing them into three general groups as 

 follows: 



(1) Those which are very resistant and are not noticeably injured by slightly 

 excessive concentrations or long exposures. Fumigation recommended as a 

 regular treatment. 



(2) Those which have consistently been injured and apparently will not 

 tolerate the treatment. Fumigation not recommended unless plants are to be 

 destroyed. 



(3) Those which fall between Group 1 and 2, being tolerant to naphthalene 

 during favorable conditions especially in experimental fumigations but ex- 

 hibiting a tendency to be injured when slightly unfavorable conditions exist. 

 Fumigation is recommended for this group only when insect injury is severe 

 and when satisfactory control of atmospheric conditions can be maintained. 

 Improved apparatus for fumigating will greatly reduce the danger of injury to 

 plants in this group. 



A list of some of the more important plants which fall in Groups 1 and 2 

 is given in Table 12. All other species are arbitrarily placed in Group 3 since 

 they have been neither outstandingly tolerant nor susceptible in experimental 

 and commercial fumigations. 



Table 12. — Tolerance of Some Common Greenhouse Plants to 

 Naphthalene Fumigation. 



Group 1. Tolerant Plants Group 2. Susceptible Plants 



Aspidistra Asparagus Ferns 



Begonia (Chatelaine) Easter Lily 



Boston Fern (Nephrolepsis) Freesia 



Cactus (Opuntia) Fuchsia 



Calendula Geranium 



Carnation Gladiolus 



Centaurea Iris 



Coleus Kalanchoe 



Cyclamen Narcissus 



Dahlia Nicotiana 



English Ivy Oxalis 



Sansevieria Physalis 



Poppy 



Radish 



Rose (Rambler and Buttonhole) 



Tomato 



Tulip 



