VALUE OF LIME IN CONTROL OF CLUB ROOT

Manawatu Times, Volume LVI, Issue 5566, 3 February 1931, Page 8

VALUE OF LIME IN CONTROL OF CLUB ROOT

Hopeful Line of Field Control PLANT RESEARCH STATION INVESTIGATES

Very valuable work in an endeavour to find a cure or preventative for club root, a disease which has ravaged the swede and allied crops in New Zealand, is being undertaken by Mr J. G. Gibbs, at the Plant Ecscarch Station, Palmerston North. Mr. Gibbs has been engaged for two years in his investigations and is now in a position to make certain recommendations to farmers, but they are based solely on preliminary experimental evidence and arc offered tentatively to relieve a serious position.

No method of complete control suitable for practical application on a farm has yet "been evolved, but the knowledge of means of dissemination the eradication of weed hosts which enable the disease to persist while a cruciferous crop is not in the ground, and the- use of club-root-resistant lines of swedes and turnips should effect a marked reduction in the severity of the disease. If slag and potash are used as fertilisers a further reduction of club-root should be effected, but manures containing superphosphate, sulphate of ammonia, and basic super are likely to increase the incidence of the disease. The most hopeful line of field control rests in lime, and if sufficient of this can be applied to “neutralise the soil-acidity and leave a moderate excess of free lime in the soil” (9) no fear of severe losses from the disease need be entertained.

Burnt lime or a freshly slaked lime offers the only hopo of producing this result at an economical cost, and ever, then must be applied well in advan.co of the date of the sowing the crop, The work has not yet proceeded sufficiently to indicate what quantity will effect this action in the soil, but it is thought that—on certain soils, at any rate —two or three annual dressings of burnt lime at 1 ton per acre should prove sufficient, or from 2 to 11 tons per aero worked into the soil about three months before sowing the crop. Where the erops grown arc of high per-acre value, such as arc produced by market gardeners, liming to the extent noeesary to control the disease would appear to be reasonable; but in the case of ordinary farm brassica crops much yet remains to be done from the standpoint of soil and climate in relationship to the disease before the economics of liming for its control can be determined. Resistance of Crucifers.

Although any cruciferous crop may be severely attacked, if not completely killed, by club-root, cabbage and rape appear most susceptible to its attacks, especially in the early stages of growth. On farms soft turnips are frequently sown in preference to swedes where club-root infection is anticipated. This is largely due to the earlier maturation of the soft turnip, which enables it to be fed off before the disease lias rendered the crop useless, as often happens with the slowermaturing swedes. The losses caused to swedes and turnips have led to the almost entire replacement of these crops by chou woollier in certain districts. Though severe infection may be artilieaily induced in cliou inocllicr, the crop is highly resistant in the field, where the yield rarely appears to suffer through club-root attacks. As a result of observations at Moumaliaki in 1911 the Superlative variety of swede was considered to be highly resistant to club-root. _ This property is not so apparent in the Superlative type of swede at present on the New Zealand market, but there is evidence of strains within the type which do not possess a degree of resistance to club-root. Unfortunately however, these lines cannot be distinguished until the crop is sown in infected ground, and then only when there is another line sown beside them for comparison. A line of Superlative swede showing such resistance was accidentally found at Palmerston North, and selection from the most resistant bulbs arc being made. At present the most resistant swede available in New Zealand is the Danish variety Horning. Trials in Otago and Southland and at Palmerston North have shown that though it is not immune to club-root this swede is decidedly more resistant than the commercial varieties at present on the New Zealand market. The overseas demand for this seed is so great that only limited quantities are available for New Zealand, -there is, however, a possibility that a fair supply may be available on the New Zealand market during the coming season. Srudsgaai'd Bangliolm suede, from which Horning’s is a selection, possesses a certain amount of resistance to club-root infection, and has been procurable in Now Zealand for several years. Crimson King swede has been twice recorded in New Zealand as the most susceptible swede to the disease. Among turnips Grocn-top and Purpletop Yellow Aberdeen 'have been noticed to show a considerable resistance to club-root infection, the former under field conditions at Gore,. the latter under experimental conditions at Palmerston North. When to Apply Lime.

Whether lime affords a commercially practical control is still to be determined. Burnt lime or cither of the slaked limes appears equally effective in control of the disease, but the commercial carbonate appears of very little use when applied at quantities less than 10 tons per acre. It also appears that the controlling influence of lime is not evinced immediately on its application to the soil. An application of 25 tons per acre of burnt lime did not control the disease until after a fortnight had elapsed, but a satisfactory control was effected with 2 to 3 tons of burnt lime applied three months before sowing th'e crop. It is probable that, the quantities of iime necessary "will vary according to the soil-types, and the determination of the mininum quantity and time of application which will effect a control of the disease is still the subject of investigation. Projected Work. Projected work and work in hand is designed to determine the longevity of the club-root spores under dry and soil conditions, and whether the disease is seed-borne. The work concerning the effect of manures on club-root is also being continued, and small lime plots arc being laid down under field conditions. Selections of seed from club-root-rcsistant lines of rape, swede, and turnip arc to be made, and further work prosecuted to determine the ex-tent-of weed hosts of club-root in New

Zealand. In the glasshouse, work is being conducted to test the effects of disinfectants and heat on the deathpoint of spores, and also the effects of soil-types on the development of the disease.