THE BLACKBERRY-BUD MOTH.

New Zealand Journal of Agriculture, Volume 5, Issue 4, 15 October 1912, Page 372

THE BLACKBERRY-BUD MOTH.

A PROMISING AGENT FOR CONTROL.

A. H. Cockayne.

In many districts in New Zealand’ the blackberry has become a very serious weed, and its control, especially in rough country and that recently converted from forest to grass, is a matter of quite grave concern. The blackberry as an aggressive weed occurs over very large areas, but it is essentially a weed of wet districts and of localities where alternate cropping is not carried out., In the purely agricultural portions of New Zealand,, as distinguished from the pastoral portions, the blackberry can never become a weed of any great importance. Wherever ploughing -is' a regular operation the blackberry, like all true shrubs, must naturally be eliminated from amongst the noxious weeds that the farmer- is likely to have to contend against on such land. In such localities it may become widespread over all waste lands, but on the arable portions it need never be feared. Thus, for instance, in districts such as the Canterbury Plains, where cropping and temporary pastures form the basis of all farming operations, the blackberry is not a dangerous problem. At the present time the blackberry is extremely serious on much land that has in recent years been converted from bush to pasture. This is especially true in such districts as the west coast of the South Island and wetter portions of the west, coast of ■ the North Island. In these districts it is not only a bad weed of the cleared country, but has also entered into the areas of standing timber, but here it is in .general restricted to the outskirts. Its Origin in New Zealand. The blackberry is one of the few pernicious of introduced plants that does not owe its origin to having been sown in agricultural seeds. ■ It being a shrub, it naturally is never found as an impurity in any seed, and, like the broom, gorse, hakea, and sweetbriar, it owes its presence in New Zealand to having been utilized for certain definite purposes before it outstepped its position as a cultivated plant and became a serious weed. Methods oe Spread.

The blackberry is spread from place to place by seed, which is in general conveyed by animals, birds being naturally the main agent in

this method of dispersal. Stock, no doubt, also, as is the case with the sweet-briar, play a not unimportant part in the spread of the blackberry. The individual plants themselves may, in a series of years, occupy a very large space of ground. The way in which the arching ■ branches bend down to the ground and then root thus virtually producing new plants —enables the blackberry to increase enormously, and in this way immense thickets quite impenetrable either to man or stock are formed. Methods of Control, The main methods of control that have been employed have been cutting and burning, followed, in the case of pastures, by keeping the young fresh growth mowed down. In country which is very rough and where stumps and logs are numerous the use of goats has been followed with most excellent results. Where the blackberries have taken • control over very large areas —and, owing to the extensive rooting of the plants, have made the ground almost impossible to stockany method of effective control must necessarily be expensive. In all such cases the increase in value of the land must be greater than the cost of control. What is really wanted is a method whereby the worst areas can be kept at a nominal cost from spreading on to ' comparatively clean land. In such cases the eradication of the weed can. be held in abeyance until such time as the cost would be commensurate with the value gained. Enemies of the Blackberry. Up till quite recently the blackberry was singularly free from the attacks of any natural enemy that might be of value in its control. For a number of years past several parasitic fungi, notably orangerust (Caeoma nitens), have been noted as occurring sporadically, but in no cases have their effects justified the •opinion that any of them would prove efficaceous as control agents. During the past two years, however, a hitherto rare native moth, Carposina adreptella, belonging to the' Tortrix group, has been found attacking the young' shoots of the blackberry. The immense numbers in which this moth has been, present, and the really effective work that it has already accomplished, indicate that it may prove an exceedingly valuable agent in controlling the spread of the blackberry. At first sight its mode of attack might lead one to think that its action would have but little permanent benefit. The eggs of the moth are laid in the leaf-bases of the young shoot or in the bud itself. The larvae, after hatching rapidly, penetrate the soft tissue and bore through the pith for a distance of perhaps 2 in. This is followed by the complete death of the terminal shoot. As has been

explained, the blackberry spreads extensively by means of pendent branches which, when they reach the ground, root and give • rise to new plants. If a blackberry-plant has the terminal portions of these branches destroyed before they - reach the ground the power to spread vegetatively is entirely eliminated, and the plant remains small in size and will not be able to coalesce with its neighbours and form a dense, close thicket. - This is exactly what is occurring wherever Carposina has attacked' the plants, and, moreover, affected plants appear to be losing their power of producing flowers and fruit to anything like the same extent as unaffected ones. I believe, indeed, that Carposina also attacks the young flower-buds before they expand, but this is a point that has not been yet investigated. The extraordinary part in the work of Carposina, and one hard to believe, is that this moth should for so many years occupy such an unimportant position in our fauna, and that within the space of two seasons it should become one of our commonest insects. The number of the larvae present on a single large' blackberry-bush is almost inconceivable, and I have seen whole areas of this weed with nearly every terminal bud eaten out and destroyed. The distribution of the moth is very widespread, and in every district I have examined the effects of its work have been most noticeable. If it continues to extend there is hot the least doubt that it will completely prevent the. blackberry from spreading vegetatively. Present indications point to its causing a great diminution in the amount of seed produced.

At present there is great need to learn exactly its life-history, as when that has been done methods may be able to be devised whereby its action may be emphasized by artificial means.

This note on the action of the moth has been written mainly to point out the really good work that this moth is silently doing in the control.- of the blackberry, and to stimulate readers of the Journal to pay particular attention to any points that may prove of value in increasing the efficiency of this enemy of one of our worst pests.