NAPHTHALENE AS A GREENHOUSE FUMIGANT 25 



Many growers have questioned the effect of subjecting carnations to high 

 temperatures and high relative humidity for 6 hours, but many experimental 

 and commercial fumigations have fully demonstrated the ability of healthy 

 plants to stand these conditions without apparent injurious results. 



Roses 



Common greenhouse roses of the hybrid tea type, such as Briarcliff , Talisman, 

 and Templar, should be fumigated only when the most favorable conditions 

 can be maintained. They cannot be treated with the heavy dosages or under 

 the partially unfavorable conditions which are tolerated by carnations. Ex- 

 cessive concentrations of naphthalene vapor due to rapid volatilization or poor 

 distribution will burn the new growth and must be avoided. Bleaching of pink 

 varieties is less likely to occur on roses than on carnations. Leaves which have 

 been loosened by forceful syringing invariably turn yellow after fumigation. 



Rambler and polyantha type roses, which are frequently forced in pots in 

 the greenhouse, are usually injured by normal fumigations and should never 

 be treated. 



Chrysanthemums 



Following naphthalene fumigation, the buds of certain varieties of chrysan- 

 themums are deformed or fail to develop. This blindness, which is similar to 

 that caused by improper application of fertilizer, appears to be characteristic 

 of this crop. The plants are especially susceptible during the period of bud 

 formation. Repeated fumigations of buds which have developed from about 

 half grown to full bloom have failed to cause this injury. Varieties appear to 

 have dFerent degrees of susceptibility, and in experimental fumigations the 

 standards, Major Bonnafon, Halliday, and Friendly Rival, and the pompon 

 Golden Nymph, were the most consistently affected, while injury to other 

 varieties has been reported by growers. Blindness did not occur when special 

 apparatus (p. 5) was used, but unless equipment of this nature is available 

 naphthalene fumigation is not recommended for chrysanthemums, especially 

 during the period of bud development and when the above-mentioned varieties 

 are grown. 



Cucumbers 



Although naphthalene fumigation in the greenhouse was first used to combat 

 the common red spider on cucumbers, this treatment is not now recommended 

 for general use on this crop. The principal reason for discontinuing the practice 

 was the fact that the fruit absorbed and retained the odor and taste of the 

 naphthalene for several days. Much of this taste disappeared after a few 

 hours in fresh air but invariably a sufficient trace of it remained to make the 

 fruit objectionable to people with a sensitive taste. On this crop the tendrils 

 are usually first to show injury, often being shrivelled when no other evidence 

 is present, and this may be followed by burn on the margin of the leaves. 

 Excessive concentrations may also injure the pistillate flowers and prevent 

 development of the fruit. Fumigations of cucumbers soon after they are set 

 in the beds and before they begin to bear will free the plants of pests without 

 contaminating the fruit; and strong fumigations just before the vines are pulled 

 out or when the house is empty is recommended as a means of eliminating 

 thrips and the common red spider between crops. 



