26 



Black Dry Rot in Swedes. 



good, and the manuring (20 loads dung, 3 cwt., vitriolised 

 bones, and 3 cwt. kainit per acre) had been suitable. The 

 land had not been under turnips for seven or eight years; in the 

 interval the field had lain for several years in grass, and every- 

 thing, therefore, was in favour of the crop of 1901. 



Two varieties of swedes and one of yellow turnips were 

 sown, and the crop was a very promising one until checked 

 by the dry weather of August and September. Mildew 

 attacked the plants, but, though said to have been worse on 

 the portion subsequently diseased than on the other part of 

 the field, it was by no means bad, and the farmer saw nothing 

 wrong until towards the end of September. Then, after some 

 days of rain, he noticed that all the swedes lost their purple 

 colour and turned a dull green ; from that time they ceased 

 growing, and underwent little outward change until the date 

 of my visit, when every root had a rough " corky " green skin, 

 and, of a number cut into, most were hollow and all were 

 diseased. I examined the whole diseased area of about 4 

 acres very carefully, and I did not find one absolutely sound 

 swede or turnip, except on a small patch of clay soil, where 

 perhaps 1 or 2 per cent, of the roots were good. On one part 

 of the affected area naturally moister than the rest, I looked 

 for sound swedes, but saw none. It was easy to detect sound 

 swedes in the field, apart from the colour. During the pre- 

 vious frosty weather the crop had been visited by hare's, 

 and every good swede had been freely sampled. None of the 

 swedes on the diseased area had been eaten into, few had 

 been touched. 



The disease, a dark brown or black dry rot, which in the 

 worst cases had eaten out the centre of the turnip, leaving 

 only a shell, was apparently due to the attacks of one or 

 more parasitic micro-organisms. Specimens have been 

 submitted to Professor Potter, who reports below the results 

 of his investigations. 



The most remarkable fact in connection with this disease 

 was that it suddenly ceased ; almost in a straight line, which 

 ran across the drills, the turnips changed to their natural 

 colour, and about one -third of each variety of turnip sown 

 was free from disease. On the unaffected part of the field a 



