Disease Wiping Out N.I. Cauliflowers

Press, Volume CV, Issue 31029, 7 April 1966, Page 8

Disease Wiping Out N.I. Cauliflowers

It was reported last week that perhaps 60 per cent of the North Island’s cauliflower crop will be wiped out by a disease this year. The disease causing the damage is black rot, a bacterial pathogen capable of severely affecting not only cauliflowers but cabbage, turnip, kale, Chinese cabbage and swedes, and other cruciferous crops to a lesser degree. It is liable to be troublesome only under very warm and moist conditions, spread being inhibited by hot, dry weather. Generally, infections start through the marginal pores of the leaves which gradually turn yellow. The chlorosis progresses towards the centre of the leaf, usually in a Vshaped area, with the base of the V towards the midrib which will become discoloured, either brown or black. This discolouration extends into the vascular system in eases of very bad infection and can be seen if the leaf stalk is snapped in haff. Young plants, especially seedlings, are killed or seriously checked while in older plants maturity may be prevented and secondary infection by the soft rot bacteria commonly follows. Sometimes when the bacteria attacks during the seedling stages conditions may become unfavourable towards further spread. In such instances the external signs of the disease may disappear for several weeks but the bacteria continues to progress slowly within the stem tissues. Infection is most usually soil borne but is also seed borne or can overwinter in diseased plant refuse. It can be further spread by transplants and local dissemination can occur by wind blown rain and even tools. For this reason growers

were warned to disinfect their seed by hot water treatment this year and to spell land previously planted to these crops for at least 12 months. It is also preferable to burn infected crop refuse and not plough it under.