November, 1911.] 



431 



Plant Sanitation. 



others, Ophionectria coccicola, E. aud 

 E., and Myriangium Duriaci, Mont., 

 upon the orange scales, is readily shown 

 by spraying an orange tree very tho- 

 roughly with Bordeaux mixture. During 

 the summer and fall of 1907, the author 

 sprayed a number of trees with Bordeaux 

 mixture tor another purpose. The trees 

 were sprayed very thoroughly, once in 

 May, ouce in July, and once in Septem- 

 ber. Before the first spraying the trees 

 were practically unhurt by Mytilaspis 

 citricola, only a few individuals of the 

 scale being found on any parts of the 

 trees. After the first spraying, this 

 scale insect began to spread, and in- 

 creased slowly in numbers until Novem- 

 ber, when the trees were badly attacked 

 by the scale. Other trees, near by that 

 had received no spray, were as free from 

 scale as at the first. The fungicide had 

 evidently destroyed, on the sprayed 

 trees, the fungi that had been all along 

 wording upon the unsprayed trees." 



Another instance illustrating the same 

 thing is that afforded by Dominica. In 

 this island there has been no serious 

 trouble from scale insects since the year 

 1903, which succeeded the drought in 

 1902. Observations on material from 

 the island show that this is to a 

 considerable extent due to the luxurious 

 growths of parasitic fungi, which have 

 kept the scales in check for seven conse- 

 cutive years. 



In their paper on ' Insects and Diseases 

 of the Orange,' Cook and Home remark 

 that the black fungus (Myriangium 

 Duriaii) has less effect on the orange 

 snow scale (Chionaspis citri) in Cuba 

 than any of the other fungi found there 

 have on the insects which they attack. 

 In Dominica, however, it would appear 

 to be more effective, for this scale prac- 

 tically never assumes serious proportions 

 in that island, and could only be said to 

 be of secondary importance in the 

 serious outbreak of scale insects that 

 occurred in 1903. The black fungus is 

 very common on this scale, and probably 

 is responsible to a very large extent for 

 keeping it under control. The same 

 fungus occurs very commonly on ihis 

 scale in Montserrat. In this island the 

 snow scale was a very serious pest in the 

 dry year 1903, but has never assumed 

 serious proportions since, except in iso- 

 lated instances where trees were suffer- 

 ing from drought. This indicates that 

 there also the black fungus is an effi- 

 cient check on this scale. The white- 

 headed and the shield scale fungi 

 {Ophionectria coccicola and Cephalos- 

 porin,™, lecanii) are equally effective, as 

 far as present observations show ; but 

 as the first only occurs in Dominica, it is 



not possible to state how useful it would 

 be under the drier conditions expe- 

 rienced in some of the other islands. 

 Experiments will, however, be made 

 to introduce it more generally, as it is 

 almost the most vigorous of these fungi 

 when under favourable conditions. 



Methods of Employing the Fungi. 



In some districts, where the general 

 conditions are favourable to their 

 growth, the parasites of certain species 

 of iusects exist naturally in large num- 

 bers. These parasites are responsible, 

 under normal conditions, for the com- 

 parative rarity of these species in those 

 districts. Such districts are usually 

 spoken of as being unsuited to the spe- 

 cies — a phrase which simply means that, 

 In the battle between the host and the 

 parasite, the natural conditions favour 

 the parasite, and the numbers of the host 

 are consequently kept at a minimum. 

 Man's work in making use of these para- 

 sites is of two kinds : firstly, to introduce 

 the parasite into districts in which the 

 conditions are favourable to its growth, 

 but in which it has not previously been 

 known to occur ; and secondly, to pro- 

 duce, where possible, by artificial means, 

 conditions which are favourable to the 

 parasites in districts where the condi- 

 tions in general are not favourable. 

 Some methods of achieving both of these 

 objects will now be dealt with. 



Three methods of introducing these 

 fungi into fields where they have not 

 previously been known to exist have 

 been found to be successful in Florida, 

 according to Dr. E. W. Berger of the 

 State Experiment Station ; but time has 

 not yet permitted of any very definite 

 observations on their effectiveness in the 

 West Indies. 



The first method consists of spraying 

 the spores aud portions of the mycelium 

 of the fungi on to the trees which it is 

 intended to infect. For this purpose, 

 leaves well infected with the fungus 

 should be stirred up for ten to fifteen 

 minutes in water ; there should be about 

 forty fructifications of the fungus, or 

 more, to each pint of water. The mix- 

 ture should then be strained through a 

 fine wire mesh, or a coarse muslin, and 

 sprayed on to the trees. The author 

 referred to above recommends that an 

 iron sprayer or atomizer should be used 

 for this purpose, or if the operation is to 

 be conducted on a large scale, a com- 

 pressed air sprayer with a galvanized 

 iron receptacle. It seems, however, that 

 if the liquid to be employed is carried in 

 a galvanized iron bucket and not in a 

 brass or copper receptacle, a brass 

 syringe might be used with perfect 



