32 FARMERS ' BULLETIN 933. 



sulphur, 1-50, may be added to this spray to increase its effectiveness 

 in killing rust mites. 



4. L(mc-su1i>hur solution, 32 Baume, 1-uO to 1-7 J November 

 or December: The object of this spraying is to kill rust mites, and it 

 may or may not be necessary, depending on the abundance of the 

 mites. 



It may be necessary to spray for rust mites and red spiders before 

 number one is given. This is especially true for grapefruit in the 

 more southern counties of Florida, If such a spraying is given, it 

 should be given in the midst of the blossoming period, using lime- 

 sulphur 1-40, which will kill rust mites, red spiders, and young 

 scales. It is advisable to add nicotine sulphate 1-1,200 if thrips are 

 abundant. It may also be necessary to spray three times with the 

 oil sprays, in which case this treatment can be given in midsummer 

 or in winter. If the red scale is very abundant, two sprayings with 

 the oil emulsions should be given at intervals of about a month. 



THE EFFECT OF INSECTICIDES ON PESTS. 



The fish-oil soap and the oil sprays kill the insects by asphyxiating 

 them. The oil sprays kill the adults, eggs, larvae, and pupae of the 

 white flies. It is not difficult to determine whether the larvae and 

 pupa? of the white flies have been killed, for they turn brownish 

 3 to 10 days after the spray has been applied. (Fig. 22.) They also 

 brush from the leaf easily. A month or more afterwards those which 

 have been killed are quite brown and somewhat dried up. 



The oil sprays kill all stages of the purple scale, and in many cases 

 all the eggs of some females are prevented from hatching. In other 

 cases the oil enters the opening in the rear of the scale covering and 

 prevents a row or two of eggs nearest the opening from hatching. 

 In the natural course of events the eggs nearest the opening hatch 

 first, since they were deposited first. This gives those young scales 

 that hatch from eggs farther from the opening plenty of opportunity 

 to emerge. When the first row or two of eggs is prevented from 

 hatching, the exit is stopped. This prevents those young scales from 

 emerging that hatch from eggs not affected by the oil film. Thus 

 almost complete mortality results. 



The oil spray kills the young stages of the red scale and in most 

 cases the adult females, but the scale covering is fastened so closely 

 to the leaf or fruit that the eggs are seldom harmed. A second spray- 

 ing must be given after these hatch and develop into the young stages. 



The sulphur sprays are extremely effective in killing rust mites. 

 The action is rapid, the bodies of the mites being largely destroyed 

 by the caustic nature of the spray. When on the fruit, a few are 

 washed to where the drop of spray collects and there their dried 

 bodies may be seen after the spray has evaporated. The eggs also 

 are killed if the spray is used at the recommended dilutions. 



