CRUCIFEROUS CROPS.

New Zealand Herald, Volume LXVIII, Issue 20823, 16 March 1931, Page 15

CRUCIFEROUS CROPS.

LOSS FROM DISEASE.

PREVALENCE OF CLUB ROOT.

SUGGESTIONS FOR CONTROL.

A heavy anuual toll is levied •on ci*uciforous crops in Now Zealand, as a result of tlio wido incidence of club root. Intensive investigational work has been carried out, and continues to bo carried out, by departmental experts, and an oxtensivo literature oil the subject has grown up both in this country and abroad. Yet the chief diminution of the loss occasioned by the disease must be attributed to decreased sowings of susceptible crops in favour of diseaso-ro-sistant substitutes and developments in grassland farming, which have rendered tlio sowing of susceptible crops less necessary. Wo know that tho development of the disease is favoured by wet, acid conditions. We can claim, on the authority of general agreement, that the use of lime and stable manure gives a slight benefit in regard to the reduction of infection. We have heard, further, the claim that the use of most artificial manures increases tho incidenco of tlio disease. And wo know that, in working affected land, strict precautions must be taken in order to prevent tho spread of the disease to clean areas. As far as definite control is concerned, however, tho position is shrouded in tho mist of obscurity, and this notwithstanding the fact that tho quest for knowledge led, as far as we are concerned, by officers of tho Department of Agriculture, has been prosecuted with vigour and intelligence. Localising tho Disease.

What may bo regarded as a summary of our present knowledge of the subject appeared in the January issue of the Journal of Agriculture, from the pen of Mr. J. G. Gibbs, of the mycological laboratory at the Plant Research Station. One of the latest investigational advances, he notes, is represented by the knowledge that as seed is sown later into tho autumn, less club root appears in tho resultant crop, a fact which lends support to the allegation of market gardeners that club root is not a menace to winter crops. The cause of this result has not yet been determined—unless the fact that the disease does not readily occur under certain soil temperatures has any significance—but tho effect has been well substantiated by test. Lacking the knowledge which leads to complete control, those measures which are known to localise the disease assume an especial importance. Mr. Gibb considers that the severity and widespread nature of the disease indicate a considerable amount of ignorance concerning the means of dissemination of tho spores and the precautions which should bo taken with land on which it is proposed to sow susceptible crops. "If it were generally known that tho spores may be transferred from infected to healthy soil in surface drain water," ho says, " with earth adhering to implements, the feet of horses and stock, on tho boots of men, and on wheels of drays, and, in the case of market gardens, by the inclusion of diseased roots in the compost heap, there would be less trouble from the disease. When it is considered how freely an affected crop may be distributed about a farm in tho operation of carting out feed to stock, and that tho distribution does not ceaso with the infected crop alone, but may in subsequent years be continued through any of the spore-laden soil being carried to other areas by stock and implements, or with soil adhering to a non-susceptible crop, such as mangels, it is not remarkable that club root appears on lea of longstanding." Earthworms, also, he says later, are said to transfer spores among the different layers of the soil, and thus may prevent a complete control by liming, through spores being brought from lower levels and causing infection of a plant before the limo in tho upper layers has an opportunity of penetrating the soil brought up by the worms.

ESect o! Manures,

The effect of manures on the development of the disease constitutes ono of tho latest phases of research. Though no manurial treatment that has been applied has controlled tho disease, it has been noted that basic slag and sulphate of potash both reduce tho intensity of the infection. Superphosphate, basic superphosphate, and mixture of super, and carbonate of lime, and super., sulphate of ammonia, and blood and bone manure, have produced plants more severely infected than those grown in unfertilised soil, but tho growth of the former has been much bettor than that of tho latter.

Whether or not tho use of limo affords a commercially practical control has still to bo determined. It is suggested that, where the crops growp are of a high per-acre value, such as those produced under market garden conditions, liming to the extent necessary for control appears to bo reasonable. In tho caso of ordinary farm crops, however, the economies of tho practice have yet to bo determined. Mr. Gibbs' suggestions for control in tho meantime are: (a) Tho application of from two to three tons of burnt limo an aero, three months before sowing; (b) tho use, where possible, of disease-resistant varieties pr strains; and (c) tho use of basic slag, as a phosphatic fertiliser, wherever this gives a good response on brassica crops.