310 



HORTICULTURE. 



Diseases 



of riant!.. 



Use of oil. 



Mildew. 



The scale. 



espalier trees. This operation may be performed any 

 time from the beginning of November till the middle of 

 February. 



549. Sir George Mackenzie has lately communicated 

 to the Caledonian Horticultural Society, the resuJt of 

 an extensive experiment of anointing the stems and 

 branches of trees with oil, or oily matter, for the pur- 

 pose of destroying the eggs and pu{c of insects. The 

 experiment has succeeded beyond expectation; but 

 care must be taken not to touch the buds, particularly 

 those which are to produce blossoms. Apricot and 

 cherry trees are the only kinds which seemed to suffer 

 injury from oil, every other kind having made vigor- 

 ous shoots, and the bark of those which had a diseased 

 appearance, having sloughed, and shown the advance of 

 new healthy bark ; and aphides, &c. seeming to have 

 been banished. 



The same gentleman has discovered a nocturnal ene- 

 my in a Curculio, supposed to be C. vastator, whose 

 ravages have been attributed to caterpillars. This kind 

 of weevil conceals itself during the day about the foot 

 of the stems of trees in the earth, from which, owing 

 to its brownish-grey colour, it is difficult to distinguish 

 it ; and at night, it crawls up and attacks the young 

 shoots and blossoms. It is very destructive to young 

 grafts. The method which Sir George Mackenzie took 

 to destroy them was, to tread the earth about the foot 

 of the stems of the trees, at night when the weevils 

 were on the trees, and putting small flat stones, pieces 

 of slate, or the like, on the trodden space. In the 

 morning the enemy having retreated under these, were 

 destroyed. The trees and grafts should, however, oc- 

 casionally be examined by candle light, and the insects 

 picked off. They have been found sometimes to har- 

 bour also in the clefts of branches, and about portions 

 of dead or decayed and rugged bark. 



550. Mildew consists in a thin whitish coating, in- 

 vesting the leaves especially of peach-trees and the 

 finer kinds of fruits. It is observed that it common- 

 ly appears in the warm months, when the ground is 

 dry, the weather calm, and when hazy vapours or 

 slight fogs appear in the evenings. It is a remark of 

 experienced gardeners, that trees washed during win- 

 ter with such a liquid as that above described, are 

 scarcely ever known to be affected with mildew, pro- 

 bably owing to the leaves being perfectly healthy and 

 able to withstand the immediate cause of the evil, whe- 

 ther it be minute fungi or the slime of aphides. Wash- 

 ing the foliage with the garden-engine is found very 

 useful in removing the mildew or in stopping its pro- 

 gress. 



551. What is called the scale seems to be the nidus 

 of an insect, or a collection of its minute eggs, covered 

 with a thin pellicle. It very much resembles a drop 

 from a spermaceti candle. The hatching of the eggs 

 and consequent bursting of the pellicle, have been ob- 

 served and described by Mr Thomas Thomson, an ex- 

 cellent Scottish gardener. It generally appears in August, 

 and it continues in the state of a scale during the win- 

 ter. The larva usually emerge about the time when 

 the trees are in blossom, and they immediately begin 

 to devour the tender parts of the flower. Afterwards, as 

 ihey acquire strength, they attack the young leaves and 

 even the new shoots of the trees. When about to un- 

 dergo their transformation, they involve themselves in 

 leaves drawn together with fine silky threads : from 

 this retreat they come forth in the form of small moths, 

 but the species has not been ascertained. The most 

 effectual method of destroying these scales consists in re- 



moving them with the nail of the finger at the time of Diseases 

 winter dressing. In rainy weather they are most dis- of t ' lltnts ' 

 cwnible, being of a lighter colour than the wet bark. ' "^v~" 

 Another simple method of overcoming them, is to make 

 a paste of fine clay of the consistence of thick paint, and 

 with a coarse brush completely to anoint the branches 

 of the tree. This should be done in March ; and if 

 heavy rains do not immediately wash away the coat- 

 ing of paint, the breeding of the insects at the proper 

 season is prevented, and their destruction thus ensu- 

 red. 



Several of the diseases of plants, we have thus seen, 

 arise from the attacks of insect assailants. Some more 

 of these remain to be mentioned, and also a few ene- 

 mies of larger size. 



Enemies to Garden Productions. 



552. Aphides or green-flies, of many species, very 

 much annoy wall-trees in the spring and early part of 

 summer, attacking the leaves while just expanding, 

 and preying much about the points of the young shoots. 

 A fumigation with tobacco is the common cure, and it 

 very generally proves effectual. In the case of wall- 

 trees, a large cloth, preferring one that is waxed or 

 oiled, is placed over the tree, and the tobacco smoke 

 applied under it with bellows ; the wall and the tree 

 are previously wetted with the garden engine, the mois- 

 ture having a tendency to detain the smoke. The 

 tree is then briskly washed with the force-pump, and 

 the border is delved over, so as to bury the stunned 

 aphides. In the same way gooseberry or currant 

 bushes may be freed from them. In hot-houses the 

 fumigation is easily performed, while the doors and 

 sashes are kept close. It is likewise very readily ac- 

 complished in melon or cucumber frames, the crops in 

 which are sometimes infested. In the kitchen-garden, 

 kidney-beans are subject to the attacks of aphides ; and 

 in the flower-garden, rose-bushes are peculiarly obnoxi- 

 ous to them. 



The Apple-aphis (A. lanigera), sometimes called Apple- 

 American blight, which has of late proved exceedingly 

 destructive to young apple-trees, first appeared in the 

 neighbourhood of London only about the year 1795. 

 It is a minute insect covered with a long cotton-like 

 wool ; it breeds in chinks and rugosities of the bark, 

 and at length almost covers the infected tree. It is said 

 that the application of the spirit of turpentine to the bark 

 proves an effectual remedy ; and we know that it has 

 been wholly banished from a garden where it had 

 spread, by merely smearing the infested branches with 

 oil, as recommended by Sir George Mackenzie. Sir 

 Joseph Banks extirpated it from his own apple-trees, 

 by the simple means of removing all the rugged old 

 bark, and then scrubbing the trunk and branches with 

 a hard brush. Mr William Salisbury, in his " Hints to 

 the Proprietors of Orchards," published in 1816, gives 

 it as his opinion.that this is the same insect which has 

 of late infested larch-trees. He supposes it to have been 

 brought to this country by the Protestant refugees in 

 the reign of Louis XIV. ; but he has assigned no reason 

 for this extraordinary opinion, nor has he attempted to 

 explain why so destructive an insect had lain dormant 

 for so many years, and at length suddenly extended 

 its ravages in so striking a manner. He observes, that 

 some of the insects descend during winter to the upper 

 roots, and lodge there ; in cleansing the trees, there- 

 fore, these should be examined, as well as the trunk 

 and branches. 



