24 MASS. EXPERIMENT STATION BULLETIN 326 



When only one species of plant is grown in a section of greenhouse naphtha- 

 lene fumigation can be adapted to the requirements of that crop, and frequently 

 a treatment can be regulated to effectively fumigate two or more species growing 

 in the same greenhouse. When susceptible plants are grown in the same 

 section with those which can be fumigated safely, those likely to be injured 

 should be removed during fumigation or the pests should be combated with 

 sprays or dusts. It is not advisable to fumigate a section of mixed plants 

 without regard for the degree of tolerance of the different species. 



A summary of the recommendations for fumigating the principal green- 

 house crops with naphthalene is given in Table 13. 



The desirability of fumigating carnations, roses, chrysanthemums, cucumbers, 

 and tomatoes is considered more frequently than the treatment of other crops 

 and, therefore, the effect of naphthalene on these plants is described separately. 



Carnations 



Naphthalene fumigation is especially recommended for carnations, and 

 fumigation with it or similar commercial preparations is now a universal treat- 

 ment for this crop throughout New England. This plant is extremely tolerant 

 to naphthalene and it has been used as the host plant in most of the experi- 

 mental work with the common red spider. More than forty varieties and 

 color strains have been fumigated with equal safety. During the winter, when 

 there is an excess of cloudy weather, pink blooms have occasionally been faded 

 or bleached slightly following fumigation, but since this effect has not been 

 consistent, the naphthalene appears to be a contributing factor rather than 

 the direct cause. Even should bleaching occur, the resulting loss or decreased 

 value of one or two cuttings is far less than the damage done by an unchecked 

 infestation of the common red spider. The most economical practice is to 

 fumigate thoroughly in the fall so that the plants enter the winter blooming 

 season free from insects and spiders which will not develop seriously at the 

 winter growing temperatures of carnations. 



When compared with water syringing as a means of red spider control, 

 regular fumigations with naphthalene produced from 14 to 21 percent more 

 marketable flowers from both good and poor crops of carnations, as shown in 

 Table 14. 



Table 14. — ■ Yield of Marketable Flowers from Carnations Receiving 

 Naphthalene Fumigation and Water Syringe. 



Waltham, Massachusetts.* 



Average Flowers Gain in 

 per Plant Fumigated 



Total Plot 



Season Cutting Period Flowers Naphthalene Water Percent 



Fumigation Syringe 



1929-30 Oct. 1 — May20t 6,165 13.07 9.76 14.52 



1930-31 Sept. 8 — May 13 2,748 6.17 4.00 21.32 



♦Records furnished by E. F. Guba from data secured in connection with studies of carnation 

 blight (Alternaria dianlhi S. & H.). 



tAverage date. Actual date on different benches varied from May 4 to June 3. 



