18 Control of the G-reenhonse White Fly 



always advisable to raise tomato plants from seed rather than to buy 

 them from mixed growers. Propagation of the new season's crop from 

 cuttings taken from old plants has also led to very serious infestations 

 and though this is not a common practice it is well to warn against it. 



Growers should realise that they are themselves responsible for the 

 heavy infestations outside the nurseries, and they should prevent these 

 by never allowing conditions inside to get bad. Very many of the 

 insects pass out of the houses of their own accord but still larger numbers 

 are taken out on trimmings and on the plants at the end of the season. 

 The pest should be kept under such control that the trimmings are never 

 heavily infested and if the plants are still infested when they are cut out 

 at the end of the season, they should be cyanided before removal. It is 

 a common practice to burn sulphur in the houses before the plants are 

 removed, but this is not a good fumigant against the white fly. 



The grower of mixed crops should free his nursery from the pest during 

 the winter by fumigations of all the occupied greenhouses and cold 

 frames. A greenhouse may be easily cleaned without fumigation by 

 completely emptying it and digging it over to bury any infested weeds 

 or leaf fragments holding pupae, leaving it empty wdth the heat on for 

 a week to starve any adults that remain and then reoccupying it with 

 clean plants. Much of the trouble with this pest, especially in Guernsey, 

 is caused by propagating tomatoes in houses containing infested potatoes 

 or beans. A small separate propagating house would prevent this early 

 infestation of the seedlings. Attacks of white fly are often caused by 

 sheltering some ornamental plants such as fuchsias in the greenhouses. 

 The specialist in tomato growing should not permit this practice. 



9. FUMIGATION. 



Spraying is of little use against white fly, while properly applied 

 fumigants give excellent results. Special attention was given to four 

 fumigants, viz. naphthalene, tetrachlorethane, tobacco preparations and 

 hydrocyanic acid gas, and these will be discussed in turn. 



(1) Naphthalene. This substance forms the basis of a number of 

 proprietary articles sold as exterminators of white fly and attention was 

 given to it for this reason. Naphthalene is sold in various forms as 

 "pure flake" which is a sublimed form: "crude naphthalene/' a dark 

 material containing carbon as an impurity and from wliich most of the 

 tarry acids have been removed; "drained salts" or "whizzed naphtha- 

 lene," a damp oily product containing a very variable amount of the 

 tarry acids; "undrained salts" or "unwhizzed naphthalene" which 



