Plant Sanitation. 



482 



[November, 1911. 



safety, provided it is emptied as soon as 

 it has been filled and had not previously- 

 been employed for fungicides. The spray 

 should be as fine as possible, as the trees 

 should be sprinkled only, not soaked, 

 any water that runs off representing a 

 direct loss of spores. If the above pre- 

 cautions are carefully attended to, it is 

 usually found that this method of arti- 

 ficial infection is the most succesef ul of 

 the three. The fungus material for 

 mixing with water may also be taken 

 from pure cultures ; purely technical 

 methods are required to obtain these, 

 but when once obtained they could be 

 kept constantly in stock in the Labor- 

 atory of this Department and distributed 

 as required, thus enabling experiments 

 to be carried on at those seasons of the 

 year when fructifications of the fungi 

 are not easily procurable in the field. 

 When it is intended to infect only one 

 or two trees for experimental purposes, 

 it may be found that a large glass 

 syringe with as fine a delivery nozzle as 

 possible is a good instrument for spray- 

 ing the trees. 



This method may be employed for all 

 the species of fungi found in the West 

 Indies, with the exception of the black 

 fungus (Myriangium Duricei). whose 

 spores are formed in such a way that 

 they would not necessarily be liberated 

 when portions of it are shaken with 

 water. The second method, which is 

 applicable to all the fungi, consists in 

 tying infected material into trees which 

 it is desired to iutect, This should be 

 done in such a manner that the fructifi- 

 cations of the fungi come into as close 

 proximity to healthy scale insects as 

 possible. This method, according to Dr. 

 E. W. Berger, ranks second in order of 

 efficiency in Florida, and should certain- 

 ly yield successful results here. 



The third method has not proved as 

 successful as the other two, and has 

 the additional disadvantage of being 

 considerably more expensive in applica- 

 tion. It consists in planting among the 

 trees to be infected, small trees whose 

 foliage is well infected with various 

 parasitic scale fungi, so that the leaves 

 of the small trees come into contact 

 with those of the larger ones. If neces- 

 sary such trees may be planted in pots 

 or tubs and raised on platforms. This 

 method has the disadvantage of not 

 spreading the fungus as effectively 

 over a wide area as in the other cases, 

 and involves certain difficulties in water- 

 ing in order to prevent the small trees 

 from dropping their leaves. 



The tying method is the one that com- 

 mends itself as that most likely to be 

 succesful here on account of the general 



conditions that prevail on estates ; 

 though spraying with spores will prob- 

 ably also prove useful, especially for 

 a small number of trees. 



In order to have a ready supply of 

 these fungi always available! it is advis- 

 able, as far as possible, for every 

 manager or planter, especially on lime 

 estates, to be acquainted with some 

 place where he can be certain of obtain- 

 ing one or more of them. For this pur- 

 pose, he should watch some particular 

 tree known to be well infested, and 

 when he notices that the scales are 

 nearly all killed, should transfer the 

 fungi to a neighbouring tree where 

 there are scale insects in considerable 

 numbers. 



With regard to the artificial form- 

 ation of conditions suitable to these 

 fungi in localities where they are natur- 

 ally unfavourable, there are two courses 

 which may be followed. The main 

 difficulties which have to be overcome 

 are the effects of a bad drought, especi- 

 ally in the dry season, and those of wind. 



In most of the islands, with the pos- 

 sible exception of Barbados and Antigua, 

 the general conditions in the wet season 

 are sufficiently favourable to permit 

 of the fungi making good growth. Con- 

 sequently, the only period when arti- 

 ficial help is necessary is during the dry 

 season ; it will probably be found that 

 spraying one or two trees with clean 

 water, once or twice a week, would 

 enable the fungi to tide over the 

 unfavoui able conditions, and so afford 

 a starting point from which they could 

 spread again in the wet season. The 

 other method, which is especially applic- 

 able in windy places, or in localities 

 where the wet season is not usually 

 sufficiently well marked to ensure the 

 spread of the fungi, is to allow the trees 

 attacked by scale insects to become 

 covered with a fairly thick growth of 

 Bengal beans (Mucuna pruriens, var.). 

 This method is particularly applicable 

 to lime trees. It has been definitely 

 proved, in Montserrat, that the cover- 

 ing of beans helps to clear the trees of 

 scale insects ; evidence too, from other 

 places, tends to support this, and to 

 show that some fungi, at any rate, are 

 more numerous in the damp sheltered 

 conditions under the beans than is the 

 case outside, it is possible that some 

 other factor or factors due to the beans, 

 which are as yet undetermined, also 

 weaken the scale insect attack. It may 

 be of interest to note in passing, that 

 the Bengal beans encourage the presence 

 of insect parasites of the scales as well 

 as of the fungoid parasites as they 

 afford shelter from the wind. 



