2 CIRCULAR 516. U. S. DEPT. OF AGRICULTURE 



than most other cut flowers, and this quality added to the gerbera r s 

 productiveness makes it deserving of the popularity it is receiving. 

 The number of plants grown by individual florists ranges from a few 

 hundred to 60,000 or more. 



Plants grown from seeds vary decidedly in form or color and 

 abundance of flowers, type and ruggedness of growth, and suscep- 

 tibility to diseases and pests. The seedlings are usually grown to the 

 flowering stage in pots or the greenhouse bench, when the inferior 

 ones may be recognized and discarded. Each of the selected seedlings 

 may be divided annually into three to five plants, and in this manner 

 stocks of uniform types may be built up and given varietal names. 

 The plants are usually grown in raised ground benches, and, after 

 they have flowered continuously from early in the fall until spring, 

 they are divided and reset during June and July. The culture during 

 the remainder of the year is similar to that given carnations except 

 possibly for the provision of a slightly higher temperature. 



Certain growers have progressed far in the development of many 

 superior varieties. Too little time has elapsed, however, for the 

 building up of these stocks to sufficient numbers to supply the general 

 growers' demand. Because of this fact many florists are not culling 

 out all the inferior seedlings and are growing many plants of rather 

 poor quality. The pest problems are serious on the latter types as well 

 as on the improved selections. 



PESTS OF GERBERAS AND THE USUAL CONTROL PRACTICES 



After the period of reestablishment. folloAving the transplanting of 

 the stock and of growth after the flowering period, the foliage becomes 

 very dense. Under these conditions it is difficult to make thorough 

 applications of insecticides to control the several pests attacking the 

 foliage and flowers. Certain of these pests, including the whitefly 

 Trialeurodes vapor ariorum (Westw.), the aphid My bus persicae 

 (Sulz.), the thrips Hercinothrips femoralis (Eeut.), Thrips tabaci 

 Lincl., and T. nigropilosus Uzel. and the common red spider, Tetrany- 

 chus telarius (L.), are usually held in check by syringing, by fumiga- 

 tion with calcium cyanide, or by spraying with various materials. 

 During the summer months, when the plants are becoming reestab- 

 lished and the foliage is less dense, the growers attempt so to reduce 

 these pests that they can be held in check during the remainder of 

 the season. A leaf miner, Agromyza pusUJa Meig., is at present com- 

 bated by picking and destroying infested leaves, or by spraying with 

 derris or nicotine extracts. This leaf miner is at times heavily para- 

 sitized by Derostenus variipes Cwfd. In contrast with their relatively 

 successful control of the above-mentioned pests obtained by one or 

 more of the methods employed, the florists have failed to control the 

 cyclamen mite by these or other treatments. 



Growers have usually mistaken the distinctive injury by the broad 

 mite for a disease or cultural trouble, and therefore effective control 

 measures against the real cause have usually not been applied. 



Several other species of Tarsonemus mites have been found asso- 

 ciated with both the cyclamen mite and the broad mite on foliage of 

 gerberas, but are more frequently found on dying or dead foliage, 

 or on foliage injured by thrips or the red spider. Judging from 



