12 



CIRCULAR 516. U. S. DEPT. OF AGRICULTURE 



variety Vesuvius or Incomparable that were immersed for 20 or 30 

 minutes in water at 110° F.. in which was incorporated glacial acetic 

 acid (1:200), formalin (1:200 to 1:600), or a mixture of formalin 

 (1 : 400) and acetic acid (1 : 200) , were either killed or severely injured 

 as evidenced by the subsequent growth. Plants were apparently 

 uninjured when treated in a bath containing acetic acid 1:400. 



Following a 20-minute immersion in water at 110° F., plants of the 

 variety Incomparable were either killed or, in most cases, were severely 

 injured by a 2-minute dip in acetic acid (1:100 or 1:200), formalin 

 (1:100), or mercuric chloride (1:1,000). Plants immersed in cold 

 dips of formalin (1:200), an organic mercury compound (1:200), 

 bordeaux mixture (4: 4: 50), or commercial dry lime-sulphur (1 : 100) 

 were apparently little affected, judging from the ultimate growth 

 attained. 



From these tests it is apparent that gerberas cannot be safely 

 treated for nematode control by immersion in water at 116° to 120° F., 

 nor can they be treated with certain common antiseptic chemicals for 

 disease control in conjunction with the hot-water treatment for mites. 

 Acetic acid (1 : 400) in the hot-water bath, or cold dips following treat- 

 ment, consisting of an organic mercury compound (1:200), bordeaux 

 mixture (4:4:50). or dry lime-sulphur (1:100), were among those 

 best tolerated bv gerberas. 



PROCEDURE IN TRANSPLANTING AND TREATING GERBERAS TO 

 PREVENT REINFESTATION 



Tarsonemid mites can be disseminated by brushing infested plants 

 or plant remnants against uninfested ones, or by the hands or tools 

 when disbudding, potting, or working among the plants. Precautions 



to prevent reinfesta- 

 tion of the plants 

 after treatment are 

 essential to obtain 

 successful control. 



The essential pro- 

 cedure followed in 

 the successful treat- 

 ment of a large stock 

 of gerbera plants 

 including 60,000 

 flowering size plants 

 and many seedlings 

 in one range of 

 greenhouses was as 

 follows : All plant 

 material was cleaned 

 out of each house to 

 be planted with 

 gerberas, manure was added to the soil, and the beds were sterilized 

 by steam through permanent lines of buried tile. A heavy application 

 of naphthalene flakes was made on the walks, and the ventilators were 

 closed for 1 week, or until replanting was started. In preparing the 

 gerberas for replanting, one group of men dug. cleaned, and divided 



Figure 8. — Vigorous new leaves gr 

 from gerbera plant crowns 10 day 

 treatment and replanting. 



vertically 

 after hot- water 



