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COPEN RECORD OFFICE

Reference -

411C.O.822/12

PUBLIC RECORD OFFICE, LONDON

ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC-

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سم

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may show until the canes are maturing or mature. In Java Dr. Wilbrink has not obtained evidence that the disease is transmitted from diseased to adjacent healthy canes; this may be due to the fact that only virgin canes are grown there and dormant infections do not have an opportunity to show up in ratoons. In Australia, North has found that aerial infection occurs to a serious degree. Infection is not transmitted from the diseased unfolded leaves to healthy leaves even through wounds such as occur readily in Gumming Disease. He believes that infection only occurs on very young tissues, especially buds (eyes), or perhaps on the very young unfolded leaves and it is not definitely known if wounds are necessary. He has recorded the frequent occurrence of Leaf Scald in patches, as if spreading around a centre, and has inferred that root to root transmission may occur when they are injured by implements. The disease is readily transmitted by the sett and into the ratoon shoots of diseased stools. He has recorded two phases of the disease—a chronic and an acute phase. The first is characterised by the presence of long narrow white leaf stripes even on the young leaves associated with etiolation and withering as the leaves age, and the development of diseased side-shoots and red fibres in the nodes and internodes which never ooze gum. The second or acute phase shows a sudden or rapid wilting of apparently healthy large stalks frequently when cool dry weather sets in. Leaf stripes, side shoots, and fibres in the nodes are usually lacking and the cane when split may look normal. The infection is re- stricted to the base of the stalk or stool and can be detected only on an occasional young shoot or sucker at the base or if that is absent, on the later ratoon shoots. This acute phase of the disease which may cause severe losses in susceptible varieties, has not been detected definitely in Mauritius; mention has been made of the wide- spread occurrence of the less injurious chronic phase on the mature stalks and young shoots of the Tanna canes, but only in a low proportion of stools, frequently only one stalk in an occasional stool. Comparative analyses by the Chemist of the Department of adjacent healthy and diseased mature stalks of White Tanna in 1928 and 1929 have shown a very appreciably lower sucrose content of the diseased stalks.

As no evidence of infection may be detected until the cane is maturing, sett' selection for the nursery should be made entirely from mature stalks, preferably from stalks in entirely healthy stools.

Leaf Scald, both in Australia and Java, and Gumming Disease in Australia, are readily transmitted from diseased to healthy cuttings by the trimmers' knives. As it is probable that, in spite of care, some obscurely or dormantly infected cuttings will be selected for the nursery, knives should be dipped in a five per cent. solution of lysol between each stroke, and if the trimming is done on a block, it should be kept wetted with the solution; Wilbrink's experiments in Java have shown conclusively that this precaution prevents transmission of infection from one cutting to another. It is useless to disinfect the setts after they are cut except as an additional precaution against Pineapple Disease. It is recommended that the same procedure be adopted in cutting up setts of seedlings selected from trial plots for larger scale field planting.

Owing to the widespread, but light, infection of Gumming Disease and Leaf Scald on the estates it will probably not be feasible to adopt in full measure the special precautions advocated by North in selecting setts from the field for planting in nurseries. Roguing out diseased young plants and a second selection from the primary nursery should, however, go far towards securing a healthy stock of cane for field planting. As the healthy stock is liable to pick up secondary infection in the field (and in the nursery if it is adjacent to fields containing diseased canes) selection must not be given up after a few years, or conditions will revert again to what they were at the outset.

Sett selection for Leaf Scald and Gumming Disease would cover selection for Red Rot, in so far as control of that disease can be effected by such selection. On the resistant varieties it is intimately connected with control of borers. It is doubtful if

any kind of selection will protect the susceptible D.K. 74 from Red Rot.

The presence and control of the other diseases on sugar-cane in Mauritius do not call for detailed reference. Mention has been made of the susceptibility of D.K.74 and M.P. 131 to Smut which may cause the loss of young shoots of virgins and ratoons during dry weather in the drier districts; with the onset of the rains the young plants usually grow away from the disease. Dastur has found that the sporidia produced by the germinating spores from the whip-like shoots can only infect young buds or old wounded buds; the mycelium develops in the tissues of the sprouting bud and, growing on in the shoot, causes the terminal leaf to be replaced

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by the spore bearing "whip' No effective practicable means of controlling the disease on susceptible varieties appears to be known.

Except in restricted localities of high rainfall where special attention must be given to drainage, the backward or stunted growth especially of ratoons (associated with root infection by soil inhabiting, weakly parasitic fungi resulting in a reduced root system) classed as Root Disease is noticeable only in and following dry weather during the growing seasons. Cane in soils which are of sufficient depth and well supplied with humus by adequate manuring and by a trash cover resist these dry weather effects; M.P. 55 appears to be more sensitive than most of the other varieties in cultivation. Root Disease has been dealt with adequately by the Mycologist in a bulletin on sugar-cane diseases (No. 32, General Series, 1926).

Pokkah Bong, due to an infection on the young folded leaves by the fungus Gibberella moniliformis Winel, has been observed, but is injurious only if the infec- tion extends into the upper joints causing the death of the growing point, a con- dition which occurs rarely on the varieties now under cultivation. In Java and Cuba the newer P.O.J. canes are more sensitive to this disease, the top of the stalk being frequently killed; it is probable, therefore, that cases of this nature will occur on the P.O.J. 2725 and 2878 now in course of introduction into Mauritius. Bunch-top, recorded for the first time in Hawaii, is a minor trouble which is being made the subject of a special investigation by the Assistant Mycologist. The leaf-spot disease known as Eyespot, due to the fungus Helminthosporium sacchari Butl., is present widely, but has not been recognised as noticeably injurious under field conditions; it has been recorded as a cause of loss on H. 109 in Hawaii and on D. 109 and B.H. 10 (12) in Porto Rico; the last-named may prove to be somewhat sensitive to this disease in the uplands of Mauritius.

Note on insect pests.

Four moth borers injure the sugar-cane in the Island; the spotted, pink, white, and brown borers, the first two doing most damage. The survey for diseases on the crop of 1928 showed a very appreciable proportion of stalks infested by borers. The most serious pest actually and potentially is the larva of the hardback, Phytalus Smithi Arr., introduced in setts of seedlings from Barbados twenty years ago. Confined at first to one locality, new and distant centres of infestation have appeared since, and it is expected sooner or later to go through the Island.

The scoliid wasp parasite of the larva Tiphia parallela was introduced success. fully from Barbados between 1913 and 1915 and effects a partial control. Active, but necessarily expensive control measures were adopted following the discovery of the pest in 1911 and are being intensified. The adult insects are collected in immense numbers under the stimulus of payment at a fixed rate per 1,000 by the Department; the larvae are also dug out from about the roots of the young cane plants or poisoned in situ. It is fortunate that the heavy infestation does not persist; it gradually reaches a high intensity during the first three or four years and then falls away rapidly, due to some unknown factor. I was given to under- stand by a number of planters that the visit of an expert on the parasites of insects would be much appreciated.

The borers, the hardbacks, and the other insects injuring sugar-cane in the Island have been dealt with very fully by the Entomologist (now Director of Agriculture and Entomologist) in a series of bulletins issued by the Department.

Mention must be made of a very effective and easily constructed fly trap invented by the administrator of one of the sugar estates. The inventor was good enough to show me the trap (it has been patented) at work, and supply plans and descriptions. The bloodsucking fly Stomoxys nigra which breeds freely in the cane trash, infests the cattle, lowers their condition, and frequently causes death. The health of the cattle has much improved on the estates (over thirty) which have adopted the trap.

General Remarks.

The secure foundation of the industry lies in the ratooning power of the canes and the responsiveness of the soil to good treatment, and in the course of my tour I was impressed by the intensive system of agriculture practised on most of the estates visited and by the evident high state of fertility of many of the fields, which should be capable of growing the best high sucrose seedlings obtainable.

Full use

is made of the factory residues, practically all the molasses, ashes, and scums going on to the land; it is the practice to apply up to 20 tons of farmyard manure to the